a

The causes of obesity are both natural and acquired. It is well Modern improvements have augmented the resources of the oboe by known that among domesticated animals some have a greater means of eleven keys, but only skilful performers can safely be trusted tendency to accumulate fat than others, and such breeds are kept up | to produce the two or three highest notes; and till very recently, E, or for the purpose. In the same way there are human beings who even c, above the staff, was considered the utmost practicable extent of exhibit the same tendency, and in the case of certain individuals the the instrument. Oboes are now frequently made to go down to Bb, most persevering measures fail to reduce their weight. On what this in which case they exceed the usual length, and have an additional tendency depends it is difficult to say exactly, but there is reason to key. believe that it depends upon the food in the early stages of digestion The oboe has for centuries past been in use, and may be traced back being converted into fat, which getting into the blood is deposited in to the reign of Edward III., in whose band oboes, under the denomi. the adipose tissue by a kind of excretory process. In such individuals nation of Wayghtes, were employed. Indeed our itinerant parishthe starch and sugar of the food appear to be more readily convertible musicians, the official precursors of what was once a merry season, into fat than in others. But whilst this tendency may naturally exist, retain the appellation of Waits, though they have long abandoned the it can be greatly increased by diet. There can be no doubt that the instruments which conferred on them their title. class of foods called carbonaceous,--starch, sugar, and fat–when taken Up to nearly the close of the last century, this instrument was only in larger quantities than are required to maintain the heat of the known, in most parts of Europe, by its French name, Hautbois, a word body, are employed in developing the adipose tissue. Experiments on which in England has always been pronounced Hoboy; and this prothe feeding of animals have shown that in proportion as these sub- nunciation has been transferred to the Italian term, though the word stances are employed in the food do they become fat. Alcoholic oboe is now invariably adopted in writing. beverages, when not taken to such an excess as to produce more OBOLUS (úßonós), was a Greek coin, both silver and brass. At disastrous results, have a tendency to produce fatness. They act in the Athens it was of silver, the sixth part of a drachma, and worth first place by stimulating the digestive process, and in the next by somewhat more than five farthings sterling. The Æginetan obolus is preventing that action of the oxygen of the air on the blood and tissues stated to have been heavier than the Athenian. It is generally by which the carbonaceous foods are oxygenated and carried off in supposed that óbolus and óbelos (oborós and openós) were originally the the form of carbonic acid. Sedentary and indolent habits also have a same word differently pronounced, and that the coin obolus was first of tendency to produce fatness. As it is by active exertion that the iron or copper, in form like a spit, which the word also means, or a oxygen of the atmosphere is introduced to the tissues of the body, and bar; that a handful made a drachme (Opayuń); and that the form was they are changed and carried away, so if this process be prevented by afterwards changed from an oblong to a round shape, but that though indolence, the tissues go on developing, and this is frequently the case struck round, like other money, it continued to retain the ancient with the adipose tissue. Heat has also a tendency to develope obesity. name. Others say that the obolus was originally so called from being Living in warm rooms, or in a warm climate, other things being equal, stamped with the figure of a skewer or spit, or other sharp-pointed has a tendency to produce fatness.

instrument. Whilst obesity is exposed to dangers of its own, a precipitate anxiety The Greeks had an hemi-obólion (quwßbalov), or semiobolus, and a to keep it down or prevent it is most earnestly to be deprecated. The trióbolon (Tpúborov), or silver coin of three oboli, which was the practice of taking vinegar to prevent obesity is attended with great common pay of the Dicastæ; the pay originally having been two oboli. danger, as it acts by destroying the digestive power of the stomach. Per. Two oboli were placed in the mouth of a dead person, in order to sons also frequently put themselves on a short diet, and without not only enable him to pay for his passage over Styx. According to Lucian, fat-forming matters but also flesh-forming matters in their food. In this Charon's demand was only one obolus. (Aristoph., ‘Frogs,' 141; Lucian, way the heart soon breaks down for want of nourishment, and death Catapl.,' i., p. 643.) occurs in a variety of ways from want of power in the central organ of According to Suidas ( Bords), the Athenian obolus contained six the circulation. The entering also at once upon a system of hard chalci (xoakoi), and the chalcus contained seven lepta (dentá). Other exercise and short sleep is frequently attended with the death of the authorities say that the obolus contained eight chalci. (NUMISMATICS.] patient. The great object of treatment should be the gradual reduc- OBSERVANTS, or OBSERVANTINS. [FRANCISCANS.] tion of the fat, whilst the muscular power, especially of the heart, OBSERVATION AND EXPERIMENT. The first of these terms should be maintained. One of the most important things to be includes a portion of the second, inasmuch as every experiment attended to is the nature of the diet. The amylaceous, saccharine, is made with a view of observing the result. But experiment oleaginous, and alcoholic parts of the diet should be diminished. No signifies more than observation, implying a disposition of means butter at breakfast, no bread at dinner, and one glass of wine a day is a of observation which it is in the power of the experimenter to make good receipt for a healthy fat man who has been in the habit of living for himself, and which he actually did make for himself. If, for indiscriminately. Hard biscuits may also be advantageously sub- example, a person who observed the attraction of the magnet for the stituted for bread. Regular exercise should be taken, never excessive. first time, dubious of the residence of the attracting power, were to Sawing, digging, walking and mountaineering according to the weight move the magnet to another place, that he might see whether the and strength of the patient are all good. Generally the obese are attracted body would still move towards it, he would make an experiinfirm of will, and this bodily state is perhaps connected with their ment. But if his magnet were the sun and the attracted body the mental condition, and of all patients they seem least able to make earth, he could only wait the proper times for observing the motion of up their minds to the necessary discipline for their cure. If the per- the latter with respect to the former, in order to establish the suasion implied in the sentence of "six months at the treadmill attraction. Thus astronomy, geology, meteorology, natural history, could in any manner be applied in their case, it would undoubtedly &c., are sciences of observation (that is, of nothing but observation); be the most effectual remedy.

while mechanics, optics, electricity, &c., are sciences of experiment. OBJECT-GLASS. The lens or system of lenses nearest the object In one sense geology and meteorology are partly sciences of experiment, in a telescope or microscope. As explained under EYE-PIECE, its since portions of the material subject matters of these sciences may be business is to form a correct image of the object within the tube; submitted to preconcerted tests. It would, however, be more proper hence it should be free from spherical aberration, and should be to consider mineralogy and aero-mechanics as the experimental sciences achromatic. For the method of rendering it so we must refer to connected with these, than to class them as mixed sciences. MICROSCOPE, and for a due understanding of the defects, to ABER- To give an account of experiment would require us to explain the RATION in optics. [ACHROMATIC; LENS; LIGHT.]

methods of every science which proceeds upon it: to give a detailed OBLATE, a term applied to a spheroid which is made by the account of observation, we should need the description of all the means revolution of an ellipse about the smaller of the two axes.

or instruments by which our senses are assisted in the examination of OBLIQUE. This term is used as opposed to direct or right, and phenomena. We shall here confine ourselves to a short sketch of the signifies whatever is not direct or right. The word seldom appears, errors which render observations discordant, and which make a final except as expressing that an angle is not a right angle, all other uses of process of combination necessary in every case in which we cannot it being almost obsolete.

command results which agree with each other so well that the difference OBLIQUITY, a term used in astronomy to express the angle made between them is imperceptible to the senses. by the ecliptic with the equator. The greatest latitude at which the Everything which is called observation is of two kinds ; in the first sun ever appears vertical is the obliquity of the ecliptic. [Sun; a simple individual fact is noted, in the second a magnitude is PRECESSION AND Nutation.]

measured. The results of the first species are the proper subjects of OBLONG, a word in common use, expressing the same meaning as, inductive reasoning only; the results of the second, of inductive and and in our opinion preferable to, the mathematical term rectangular, mathematical reasoning, either or both. Individually, the first kind of or having the figure of a rectangle.

observations are not necessarily subject to error; thus a zoologist OBOE (Ital.), a musical instrument of the pneumatic kind, blown observing the structure of a new animal might in every instance through a reed: it is a tube of boxwood, 22 inches in length, correctly note the resemblances which exist between it and other slender in the upper part, but spreads out conically at the lower end, animals, and might refer it to its proper class in a manner which and consists of three joints, or pieces, besides the reed. Its compass centuries of succeeding observation would not induce naturalists to is two octaves and a fifth, from c below the treble clef, to o, the fourth disturb. Collectively, however, wrong inferences might be drawn added line above it:

from facts; thus results of classification which are true of all animals
known up to one moment, and are therefore inferred to be always
true, may be disturbed in the next moment by the discovery of a
new specimen.

Observations of the mathematical character arc of necessity erro

neous from the imperfections of our senses. When a new insect is than B. Now, if A and B were to observe together for a century, the observed, it is soon seen, for instance, whether it has or has not mere comparison of their observations, though it would settle their wings, and the question once settled is finally settled. But when, say average amount (of difference, would never enable us to give the least the specific gravity of a gaseous substance, at a given pressure and guess which of the preceding cases is the true one. If indeed we could temperature, is measured, it is impossible to consider the question as convert the observer, as we have previously mentioned might generally settled at any time. Say that, under given circumstances, the specific be done with the instrument, into another observer with an error of gravity is asserted to be :934 of that of air similarly circumstanced; the opposite kind, a true result, or one sensibly true, might be obtained. this is only an admission, at most, of its being somewhere between Suppose, for example, it is the observer's habit, in noting the transit •9335 and 9345. And that which we call an exact measurement of a of a star over a fixed wire in the field of a telescope, to take the transit length may for one purpose mean within a hundredth of an inch, for too soon when the star comes in on the right side, and too late when another within a thousandth, and so on; but no person dreams of on the left: consequently, by making a number of observations with having attained absolute truth. This being well known, and every an inverting telescope, and an equal number with one which does not process used in observation being subject to error, it is the business of invert, the average of both sets would be as likely to give a true result the observer to repeat observations many times, and to extract a result as if neither error had existed. [EQUATION, Personal.] es near to the truth as may be, from the mass of discordant materials All the errors which precede, though called errors because they give which the repetition will furnish.

a result which is not the one intended to be obtained, yet are in fact The necessary errors of observation arise from the imperfection of the consequences of an actually existing state of things, and their laws our perceptions and of the instruments which we use, and also from can be determined by using the right means, or at least must be hasty or otherwise incorrect conclusions. The subject requires the supposed to arise from natural causes measurable by experiment in the separation of these errors into three classes, which may be mixed up same manner as other consequences of existing relations. They are with one another in results, and may be mistaken for one another. We then really measures of phenomena, called errors simply because the may call them fized, personal, and casual.

effects of their causes are to be removed from the results. It is even By a fixed error we mean one which is inherent in the instrument possible that they might be made intentionally in a given form, with a or method employed, so that it must exist, and, all other things view to prevent their occurrence in a more objectionable form. Thus, remaining the same, must have a given magnitude. Thus, if the axis suppose an observer finds himself, in correcting discordant observations, of an equatorial (supposing such an instrument to be employed for apt to confound additions and subtractions, using one for the other : absolute measurements) do not absolutely coincide with that of the he will set his instrument intentionally wrong to an amount which heavens, the right ascension and declination of a given star, measured casual discordances never reach, taking care, of course, to preserve when at a given distance from the meridien, must have a given error. means of correcting the intentional error with the rest; so that the It might be precisely the same in numerical effect, and would certainly requisite correction shall always be of one kind, additive or subtractive. produce an error of the same class if the observer used a wrong Nevertheless this arrangement, as it should be called, would go by the formula in the reduction of his observations. Thus, it would be name of an error, simply as being to have its effect afterwards destroyed. perfectly possible to give to one observer an incorrect instrument By casual errors, the only ones to which the name of errors can and a correct formula, and to another a correct instrument and an properly be given, are meant those which are absolutely inexplicable, incorrect formula, in such manner that their final results should or of which the cause and tendency are equally unknown. They must coincide.

be considered as equally likely to be positive or negative; so that in Errors of this kind cannot be detected by multiplying similar obser- the long run the results which they give too great will be compensated vations, since there can be no tendency to destroy error in the mere by those which are too small. If this be not the case, that is, if there repetition of it. There are many modes of detecting fixed errors, and be a greater tendency to too much than to too little, there must be a of allowing for them; but the only mode of avoiding them is by taking reason for this phenomenon, and a law of action, which must be sought advantage of the construction of the instrument to use it for the same for and detected. Let us suppose this done, so that any result of a purpose under different circumstances, in such manner that measure single observation, corrected for all discoverable sources of error, is in ments which are too large in one set of results must be as much too small itself as likely to be too small as too great. in the other. If the same number of observations be contained in each If all the observations be equally good, the MEAN, or average, is set, this, as we shall presently see, is really a reduction of the fixed more likely to be true than anything else. This is even true with error to the class of casual ones; or rather, a destruction of the fixed reference to fixed or personal errors which may remain, but which are error by the same process which gives the highest probability of totally unsuspected; for there is an even chance of such errors acting destroying the casual errors.

in either way. In the article just cited is shown the way of finding, All instruments must be more or less erroneous in every particular. from the observations themselves, the probable error, as it is called, or In the science of observation, as now understood, and in any matter in that which there is an even chance of not exceeding; with references which the utmost attainable exactness is requisite, the assumption of to further sources of information. This article (MEAN), together with perfection in an instrument, in any point whatsoever, is looked upon as the general considerations in PROBABILITIES, THEORY OF, and WEIGHT nothing but the expression of the observer's unwillingness to take OF OBSERVATIONS, will contain all we shall find it necessary to say on trouble. For even if ninety-nine successive days' trials have shown the subject. that any particular error does not exist to any sensible amount, It might be supposed that the greater the number of observations, it is not conclusive against the observations of the hundredth day the leas, in the same proportion, the probable error of the average; being affected by some new circumstance, necessary or accidental, in but this is not true, since the probable error diminishes as the square which the instrument has been placed in the intermediate time. ront of the number of obseryations increases. Thus, suppose it to be By a personal error is meant one of the same character as a fixed well settled that twenty observations of a given observer will have an

but arising from the temperament or habits of the observer, average of which it is an even chance that it does not err by (say) a and not from the instrument. Thus if A should, in noting the time unit: then the same observer must make four times as many observaof a phenomenon by the clock, have a tendency to accelerate the tions to get an average with an even chance of not more than half a moment of its happening, and B a similar tendency to retard it, the unit of error; nine times for one-third of a unit, and so on. results of the two would differ by the sum of their personal Those who neglect sound principles of observation are apt to over

It has been discovered that two individuals, observing rate the effect of multiplying observations; which, though considerable, the same phenomenon with the same species of instruments may does not, as we see in the above rule, keep pace with the number of differ sensibly (though but little) from each other; and this not observations. once or twice, but nearly always, and in such a manner as to make OBSERVATORIES, ASTRONOMICAL. We possess only an imthe average of a set of observations of one observer differ from perfect knowledge respecting the institutions established in ancient that of the other. For anything we can know to the contrary, times for the observation of the heavenly bodies. The observatory of this species of error may exist in every observer; and its absolute Alexandria is alone famous in the history of Greek astronomy. It was quantity must be unknown until we can compare the observations there that the observations were first made, upon which astronomy as of men subject to it with those of some other beings who are not. If a science, in the true sense of the term, was finally founded. With indeed the personal error be purely casual, so that where one person the revival of science in modern Europe, the establishment of observameasures too much, another measures as much too little, the average tories was soon felt to be indispensable to the progress of astronomy. of the results of a large number of observers would give the truth or The observatory of Tycho Brahé, erected in the island of Huena very near it. But should it be the case, which is not impossible, that towards the close of the 16th century, under the auspices of Frederick all men are subject to an error of the same kind, some more and some 111., king of Denmark, is memorable in the history of astronomy for less, namely, that all measure more or less too much, or else, that all having supplied the facts which enabled Kepler to destroy the epicymeasure more or less too little, the average above mentioned would clical mechanism of the planetary movements, and to substitute in its give, not the truth, but the truth affected by the average error of all stead the true theory of elliptical motion. About the same time the observers. Nor would the results obtained ever enable us to dis- William, Landgrave of Hesse Cassel, did good service to astronomy by tin:ruish whether personal errors have a fixed average or not; for the erection of an observatory, and the prosecution of a series of eppose the fact observed to be that A, one time with another, mea-observations of the heavenly bodies. The lustre shed upon his sures more than B; this may mean either of several things :- either a country by the labours of Tycho Brahé doubtless acted as a powerful measures truly, and B too little; or B measures truly, and A too incentive in stimulating the Danish sovereigns to patronise astronomy. much; or B measures too little, and A too much ; or both measure We accordingly find that the earliest national observatory of modern too little, but B more than A; or both measure too much, but A more Europe was established in Denmark. The observatory of Copenhagen

error,

a

moon.

was commenced in 1637, but it was not completed until the year 1656. and reflected vision. The objects of his labours, besides the sun, moon, The first astronomer who was appointed to the direction of its labours and planets, included also a considerable number of the stars. The was Longomontanus, the celebrated pupil of Tycho Brahé.

observations in right ascension at the Royal Observatory, subsequently In the latter part of the 17th century a great impulse was given to to the year 1816, were made with a new transit instrument of ten feet practical astronomy by the invention of the micrometer, and the appli- | focal length, constructed by Troughton. In 1833, Pond published a cation of telescopic sights to the observation of the heavenly bodies. catalogue of 1112 stars, which proved of great value to the practical During this period the observatories of Greenwich and Paris were astronomer. He retired from office in 1835, and died in the following erected. We proceed to give a brief sketch of the history of the year. former of these institutions, although as regards priority of establish- Pond was succeeded by Mr. Airy, who still continues to hold the ment the Paris Observatory has the advantage by a few years. office of Astronomer Royal. He had been previously Plumian Professor

The Royal Observatory of Greenwich was established in the year of Astronomy in the University of Cambridge, and had also been 1675. The foundation stone of the building was laid on the 10th of Director of the Cambridge Observatory since the year 1828. While August, and it was finished in less than twelvemonths afterwards. engaged in the latter capacity he set the example of reducing all his Flamsteed was appointed Astronomer Royal, with a salary of 1001. a-year. observations as soon as they were made, a practice which has since In the warrant of Charles II. for the payment of his salary, he is styled been adopted at all public observatories. This eminent astronomer

our Astronomical Observator;" and he is directed “ forthwith to apply has signalised the period of his career at the Royal Observatory by himself with the most exact care and diligence to the rectifying the numerous operations of great importance. Upon his recommendation, tables of the motions of the heavens, and the places of the fixed stars, the Lords Commissioners of the Admiralty defrayed the expenses of so as to find out the so much desired longitude of places for the per- reducing all the observations of the moon and planets made at Greenfecting the art of navigation.” Flamsteed took up his residence at the wich from 1750 to 1830. The results for the planets were published Observatory on the 10th of July, 1676, and shortly afterwards com- in 1846, in one quarto volume; those relating to the moon were given menced his duties as an observer. In this capacity he continued to to the public in 1848, in two large quarto volumes. Several important officiate till his death, which occurred towards the close of the year catalogues of stars have emanated from the Royal Observatory during 1719. His observations are collected in an important work, entitled Mr. Airy's directorship. [ASTRONOMY.] In the instruments of the "Historia Cælestis Britannica,' published in three volumes folio; the Observatory great improvements have also been effected. In 1847 an third volume contains a catalogue of 2935 stars, reduced to the begin. altitude and azimuth circle of a peculiar construction (termed an ning of the year 1689.

altazimuth) was erected, for the special purpose of making observaThe second director of the Greenwich Observatory was the cele- tions of the moon out of the meridian. In 1851 a powerful transit brated Edmund Halley. His earliest observation is dated October 1, circle was erected, and henceforward all observations, both of right 1721. His labours were chiefly confined to observations of the ascension and polar distance, were made with the same instrument.

The results of these observations are inserted at the end of In 1852, an instrument termed the reflex zenith tube was erected, his planetary tables, published in 1749. No other observations made the object of which is to make observations near the zenith, mainly for by this astronomer during his directorship of the Greenwich Observa- the purpose of determining the value of aberration. In 1853 the tory have been published. The original records of his labours are American method of recording transits of stars by electro-magnetism deposited in the Royal Observatory in four small quarto volumes. was introduced at Greenwich. In 1859, observations were commenced Upon the recommendation of Francis Baily, a copy of these observa- with a magnificent equatorially mounted refractor of 12 inches aperture. tions was taken by order of the Lords Commissioners of the Admiralty, It may be remarked, finally, in connection with this brief sketch of the and presented to the Royal Astronomical Society in the year 1832. Royal Observatory, that a great number of chronometers for the Halley died on the 14th of January, 1742.

Adiniralty are being constantly rated at the same establishment. Halley was succeeded in the office of Astronomer Royal by Bradley, The other public observatories of the British Isles are those of who had already rendered his name for ever illustrious by his dis- Oxford, Cambridge, Portsmouth, Durham, Liverpool, Edinburgh, covery of the aberration of light. In 1749, the Observatory having Glasgow, Dublin, and Armagh. Of private observatories may be menbeen furnished with a brass quadrant of eight feet radius, constructed tioned the following :- The observatory of Mr. Bishop, Regent's Park ; by the celebrated artist, Bird, Bradley commenced a series of observa- the observatory of Mr. Warren De La Rue, Cranford, Middlesex; the tions with the new instrument, which he continued to prosecute till observatory of Mr. Carrington, Redhill; the observatory of Mr. Whitshortly before his death in the year 1762. The results of his labours bread, at Cardington, in Bedfordshire; the observatory of Dr. Lee, at were subsequently published at the expense of the University of Hartwell; the observatory of Lord Wrottesley, at Wrottesley Hall; Oxford in two folio volumes, the first volume in 1798, under the the observatory of Mr. Lassell, at Bradstones, near Liverpool ; and the superintendence of Dr. Hornsby, and the second in 1805, under the observatory of the Earl of Rosse, at Birr Castle, Ireland. editorship of Dr. Robertson.

The Royal Observatory of Paris was commenced in the year 1667, Bradley's observations of the stars have been reduced and discussed but was not completed until 1671. Its early history was illustrated by the celebrated Bessel in a work published at Königsberg, in one by the labours of Dominique Cassini and Picard. M. Le Verrier, one volume folio, in the year 1818, entitled, Fundamenta Astronomiæ pro of the independent discoverers of the planet Neptune, is the present anno 1755, deducta ex observationibus viri incomparabilis James Bradley, director of that establishment. The only other public observatories in specula Astronomica Grenovicensi per annos 1750-62 institutis.' of France are those of Marseille and Toulouse.

Bradley is universally regarded as one of the greatest observers of Perhaps no country in Europe is so richly endowed with public ancient or modern times. The year 1750, when he commenced his observatories as Germany. In the north of Germany we find the labours with Bird's quadrant, may be considered as the epoch whence observatories of Berlin, Königsberg, Breslau, Bonn, Göttingen, Gotha, date observations comparable in precision with those of the present and Hamburg; in the south there are the observatories of Vienna day. Henceforward the observations made at Greenwich have been and Munich. The observatory of Königsberg is celebrated for having employed almost exclusively in all the more important investiga- been the scene of the labours of the illustrious Bessel. tions of astronomy. Nor must we omit to state, that it was during In Italy there are numerous public observatories, of which the most his career as Astronomer Royal that Bradley made the series of famous is the observatory of the Collegio Romano, Rome, directed by observations, which resulted in his great discovery of the nutation of the distinguished astronomer, Professor Secchi. the earth's axis.

In Russia great efforts have been made during the present century The successor of Bradley was Dr. Bliss, Savilian Professor of to promote the cultivation of astronomy. The Imperial Observatory Geometry in the University of Oxford, who died in 1765. The next of Pulkowa, directed by the celebrated astronomer M. Struve, is perhaps Astronomer Royal was the famous Dr. Maskelyne. His observations the most magnificent institution that has ever been established for the embraced the determination of the positions of the sun, moon, and advancement of practical astronony. There is also in Russia the planets, and a select number of stars; and he continued to adhere to observatory of Dorpat, directed by Professor Madler; and the obserthis plan throughout the whole period of his career. Maskelyne first vatory of Moscow, of which Professor Schweizer is director. introduced the practice of observing the transit of a star at five Observatories have been established throughout the other countries of vertical wires of the telescope. He was also the first who noted the Europe. A list of these establishments is given in the article AstroxOMY. transit of a star in terms of tenths of a second. His death occurred in In the United States of America great progress has been made the year 1811. The results of his observations have been published during the last quarter of a century, in the cultivation of practical in four folio volumes.

astronomy, and a number of flourishing observatories are now in Maskelyne was succeeded by Pond, who had already distinguished active operation. Of these the most celebrated are the National himself as a practical astronomer, having in the year 1806 communi- Observatory, Washington, and the Observatory of Harvard College, cated a paper to the Royal Society, in which he demonstrated that the Cambridge, Massachusetts. brass quadrant of the Royal Observatory had undergone a change of OBTUSE, opposed to acute, is applied to an angle which is greater forni since its erection in Bradley's time. It was doubtless this than one right angle and less than two. circumstance which induced Maskelyne to solicit from the Government OCCULTATION. This word, which might serve to design any the construction of a mural circle of six feet diameter by Troughton, a eclipse of one heavenly body by another, and even the effect of cloud request which was complied with ; but the instrument was not quite or fog, is particularly applied to the eclipse of a fixed star by the moon. finished at the time of his death. Soon after his accession to the office It has been seen (Moon) that the spiral course of the moon's real orbit of Astronomer Royal, Pond commenced a series of observations with the must bring her at some time or other in the course of a revolution of mural circle, in the prosecution of which he evinced a high degree of the nodes (18 years) at or near to every star situated within about 5° talent. He first introduced the practice of observing a star by direct of the ecliptic either way. There are consequently continual occul.

ARTS AND SCI. DIY. VOL. VI.

6

tations of stars by the moon; such of which as can be made useful in the bright rings which surround the image of a star as seen in a good finding the longitude are given yearly in the 'Nautical Almanac.' telescope. It is plain also, for the same reason, that the aggregate of

If the moon were (like the star) so distant that two spectators at light produced by the aggregate of all the luminous points of the nearly opposite points of the earth would not be sensibly removed from moon's disc, is not a luminous image bounded by a sharp outline, at each other in space when their distance from each other was compared what we consider the geometrical outline of the image, but that the with their common distance from the moon, then all observers, where- geometrical outline is fringed by a band of illumination, produced by soever situated, would see the moon begin to hide a star at the same the interlacing and superposition of all the systems of rings. Hence it instant. They would all then be able to nute by their different clocks follows that when, with a very fine telescope we see the moon’s limb the absolute instant of the same phenomenon; and (LONGITUDE) their very sharply defined, and apparently surrounded by immediate differences of clock-time at this absolute instant would give their darkness, we do in reality see it erroneously. Mr. Airy conceives that differences of longitude. But the proximity of the moon makes it during ordinary observations of the moon, the conviction that the possible that one observer (at A) may see no occultation at the time outline of light ought to correspond to a given curve, may affect the when such a phenomenon has occurred to another (at B); and makes it visual organs so as to incapacitate them from perceiving the fainter

light beyond that curve; but that in the excitement and intentness of observing an occultation, the state of the sensational organisation is probably much changed, and as the presumed time of the phenomenon comes nearer and nearer, the eye probably becomes more and more sensible to the faint diffused light, and the visible boundary of light extends further and further into the darkness. In numerous instances when the boundary of the moon's light has swelled till it touches the star, it swells no further, and the star hangs on the moon's limb. According to Mr. Airy, it seems perfectly conceivable, that the mental

contemplation of the relation of the positions of the moon and star certain that two observers cannot see the beginning of an occultation which is implied in the phenomenon that is to be observed, may at the same instant of absolute time. Both therefore must deduce frequently so far act on the sensibilities, that when that relation from their own observed times of commencement, and from their (namely, contact) is once gained, the mental effort does not make the knowledge of the moon's place and motions, the times, at their several sense more acute than is necessary, and may even somewhat relax as places, at which a spectator situated at the earth’s centre would see the the denser light of the moon reaches the star. This explanation, it star touch the moon's limb; and this being done, they are in the same will be seen, refers the phenomenon to the principle of the irradiation position as if the moon had been too distant to require such a process. of light. If, in this work, we had given the details of astronomical calculations, OCCUPANCY. This term in English law signifies the taking we should not have separated that required in reducing an occultation possession by any person of any thing which has no owner (Bracton, to the earth's centre from the similar case which occurs in an eclipse fol. 8,6), and the general doctrine, as stated in Bract is derived of the sun or a transit of Venus: the principles employed in all are from the Jus Gentium of the Roman lawyers, as explained in the identical, though the first process is rendered more simple than the Digest' (lib. 41, tit. 1, s. 1, 3, 5, &c.). That use of the term which second or third, by the very great distance of the star, which may be will be here explained has reference to the occupation of land. considered as marking the same point of the heavens at all places. For An estate pur auter vie, or for the life of another person or persons, the value of observed occultations in finding the longitude, see the had formerly some peculiar qualities incident to it. If a man had an article LONGITUDE.

estate in land for his own life, such estate was of course determined by Here we might close this article, if it were not for a singular cir- his death. But if he had an estate in land for the life of another cumstance which sometimes occurs; and which cannot be traced either person, and he or his assignee died before such person, the estate was to the character of the telescope employed, of the observer, of the not determined, and yet there was nobody to take it, inasmuch as it weather during the observation, or of the particular star under occulta- could not go to the heir, nor, being a freehold interest, to the executor tion. When the moon approaches the star, instead of an instant of or administrator. Such an estate belonged to the first person who

contact, followed by disappearance of the star, the could take possession of it, and he was entitled to hold it as general latter for a few seconds is frequently thrown upon the occupant till the expiration of the life for which it was originally moon, as if it were the nearer body, and were going to granted. But if the original grant were to A and his heirs, for the life cross the moon's surface, as Venus does that of the sun of B, and A died during the life of B, the heir of A took the estate as

during a transit. While this is taking place, which special occupant—that is, as a person designated in the original grant. ☆

sometimes lasts until the star has fairly left the moon's Sometimes the heir was said to take the estate as a descendible freelimb or border, the star preserves its light, though it hold, though the estate is admitted not to be an estate of inheritance,

frequently undergoes a change of colour. Aldebaran, and therefore not subject to courtesy or dower,-it not being perceived whose natural colour is inclining to red, has been seen to present this that to say an estate is not an estate of inheritance and yet is descendphenomenon much more frequently than any other star : but o Tauri, olible, is a contradiction, for descent implies an heir who takes as heir. and 82 Pleiadum, Spica Virginis, Regulus, y Libræ, 132 Tauri, al Cancri, Still it appears from Bracton (fol. 26 6, 62 6), that if lands were given 49 Libræ, 1 Aquarii, 249 Aquarii, 187 Sagittarii, „ Tauri, Leonis, ē to a man and his heirs for the life of another person, the heir could Geminorum, 8 Cancri, 8 Piscium, &c., have been seen more or less to recover the land by an assise of mort d'ancestor, because the ancestor come upon the moon's limb. See a detailed list of quotations from died seised as of fee, and a man could claim by an assise of mort the different observers in a paper by Mr. South, On the Occultation d'ancestor any land of which his ancestor was seised as of a fee (ut de of o Piscium by the Moon,' in the third volume of the Memoirs of feodo); and hence it has been concluded that the heir took not as the Astronomical Society.'

. It is to be noted that many of these special occupant, but that he took a descendible freehold. This subject appearances did not exhibit the whole of the phenomenon, but made of occupancy, general and special, is discussed at great length and with the star hang for some seconds upon the moon's limb, instead of considerable acuteness by Vaughan, Justice. (Vaughan, Holden v. immediately disappearing.

Smallbrooke.) The occultations of Aldebaran approaching again in the years 1829 In the case of copyhold, when there was no special occupant, the and 1830, the Society just mentioned invited the particular attention lord took the estate; for the lord, having the freehold, was also conof astronomers to them. The consequence was, a large number of sidered to have the possession; and therefore “vacancy,” the necessary communications from different parts of Europe, which are printed in condition to any other person's title by occupation, was wanting. In the fourth volume of their Memoirs. Nothing can be more different the case of a rent or other incorporeal hereditament, when there was than the results : some, now saw the phenomenon for the first time; no special occupant, inasmuch as there could be no entry, there could others, who had seen it before, did not see it; some, who had never of course be no possession or title by general occupancy. seen it before, continued unable to do so. Of six observers at the It is stated by Bracton, that if land was given to a man for the life Royal Observatory, five distinctly saw the projection on the moon's of another without any mention of his heirs, the land on the death of limb, and one saw it hang on the edge of the moon five or six seconds the donee did not immediately revert to the donor, unless the donee before it disappeared. Of three at the Observatory of Paris, two died intestate, or unless, though he made a will, he had made no distinctly saw the projection, and one saw the star disappear instan- mention of his interest in the land as of a term of years, but that if taneously, leaving a shade (“ombre") on the part of the moon at which he had disposed of it in his will as of a chattel, such disposition was it disappeared. The majority saw the star either projected or hanging valid. (Bracton, fol. 27 a; see Doe dem. Blake, 6 T. R., 291.) This on the moon's edge. It is to be noted that this phenomenon has been power of disposing of a freehold interest in land must have fallen into seen at the dark edge of the moon as well as at the enlightened. Its disuse after the time of Bracton; for it is quite inconsistent with the cause is matter of much diversity of opinion.

doctrine of general occupancy as stated by Littleton, and also with the The most recent explanation is due to Mr. Airy, who in the year general rule of law, which prevented freehold interests in land from 1859 communicated a paper on the subject to the Royal Astronomical being disposed of by will, before the Statutes of Wills passed in the Society, which is to be found in the twenty-eighth volume of the reign of Henry VIII. But the Statutes of Wills were limited to

Memoirs' published by that body. Mr. Airy remarks, “ that on the estates in fee simple, and no power to devise estates pur auter vic principles of the undulatory theory of light, the image in a telescope existed at law before it was given by the Statute of Frauds. of any luminous point, whether a star or a portion of the moon's Since the passing of the Statute of Frauds (29 Car. II. c. 3), general illuminated surface, is not a point." This is exemplified in the case of occupancy (with, perhaps, one exception, hereafter mentioned) has