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he obtains a series of measures differing from the true height-those corresponding to the hottest hours being in excess, and those appertaining to the coldest hours in defect of the true height. He then ascertains the amount of correction which, being applied to the mean sum of the readings of the thermometer at each epoch in each of those months, would bring out the true height. In this manner he obtains a table, showing what he calls the normal correction for each of the nine epochs of the day during the four summer months. There is good reason to believe that, in reducing barometric observations which are to be compared with Geneva and the St. Bernard, the application of the normal correction ascertained in the manner above stated will in general give truer results than those where this is not applied; but as it is obvious that the conditions of temperature at the moment when a given observation is made are constantly varying from the mean of the corresponding day and hour, it follows that a further supplemental correction should be made on this account.

To apply this further correction is a matter of no slight difficulty. The method employed by M. Plantamour is as follows. He obtains from the observations at Geneva and the St. Bernard (by interpolation when necessary) the elements corresponding to the day and hour of the observation which is sought to be reduced, and from these he calculates the height of the St. Bernard. The height so obtained, when compared with the measure which is derived from the mean of the readings for the same day and hour, as shown in his Table of normal corrections, furnishes a criterion by which to judge of the conditions with respect to temperature of the moment when the observations to be reduced were made. M. Plantamour thinks it not difficult to infer from the observations themselves, and from the general state of the weather at the time, whether the moment was one of atmospheric equilibrium or the reverse. In the latter case the observation is treated as one of inferior utility, to which a lower value should be assigned in the final 'calculation. Supposing, on the contrary, the observations not to betray a disturbance of equilibrium between the two stations, the deviation of the height, as calculated for that particular moment from the height derived from the corresponding means, is the measure of the amount and sign of the supplemental correction corresponding to the moment of observation.

Without entering at present into sundry points of secondary importance, the writer believes that, while it is at present impossible to clear the mode of dealing with this correction of some arbitrary elements, it is easy to adopt a system less cumbrous and less inconvenient, and at least equally accurate with that proposed by M. Plantamour. He finds that many of the observations which appear to M. Plantamour to be clear of anomalies arising from the disturbance of atmospheric equilibrium, show unequivocal traces of such disturbance. These anomalies can be eliminated only by comparing the observations in hand with many different standard stations, such as Milan, Turin, &c. ; but, in the absence of direct evidence, the introduction of an empirical correction in the manner proposed is likely to lead to

error.

The writer proposes to deal directly with the correction for temperature upon the best information that is available in regard to each of the stations where observations are recorded. He considers that the deviation of the thermometer at the time of observation from its mean height at the corresponding day and hour, is a tolerably accurate measure of its greater or less deviation at that time from the true temperature of the air freed from surface-radiation, and may therefore be taken with its proper sign for the supplemental correction.

It is important that the comparison between Geneva and St. Bernard, made by M. Plantamour, should be extended to other stations near the base of the Alps, and for this, as well as other reasons, it is highly desirable that the observations at Milan and Turin should be made at hours which correspond with the Swiss observations.

On the Extent of the Earth's Atmosphere.

By the Rev. Professor CHALLIS, M.A., F.R.S., F.R.A.S.

The object of this paper was to show that the earth's atmosphere is of limited

extent, and reasons were adduced, in the absence of data for calculating the exact height, for concluding that it does not extend to the moon. It was argued on the hypothesis of the atomic constitution of bodies, that the upward resultant of the molecular forces on any atom, since it decreases as the height increases, must eventually become just equal to the force of gravity, and that beyond the height at which this equality is satisfied, there can be no more atoms, the atmosphere terminating with a small finite density. It has been generally supposed that the earth's atmosphere is about 70 miles high, but on no definite grounds, and the estimates of the height have been very various. Against the opinion that it extends as far as the moon, it was argued that, as the moon would in that case attach to itself a considerable portion by its gravitation, which would necessarily have some connexion with the rest, there would be a continual drag on the portion more immediately surrounding the earth, and intermediately on the earth itself, which would in some degree retard the rotation on its axis. Hence if, as there is reason to suppose, the rotation be strictly uniform, the earth's atmosphere cannot extend to the moon. author also stated that if by balloon ascents the barometer and thermometer were observed at two heights ascertained by observation, one considerably above the other, and both above the region in which the currents from the equator influence the temperature, data would be furnished by which an approximate determination of the height of the atmosphere might be attempted.

The

On the "Boussole Burnier," a new French Pocket Instrument for measuring Vertical and Horizontal Angles. By F. GALTON, F.R.S., F.R.G.S. This instrument is about 3 inches long and inch deep. Its outside is composed of two faces of brass with pear-shaped outlines, separated by vertical sides. In the body of the instrument are two delicate circles placed in parallel planes; at its smaller end is a cylindrical lens, which views the nearer graduations on the rims of the two circles; on the upper face of the instrument are sight-vanes like those of an azimuth compass; on the lower face is a light universal joint, which is used when the instrument is attached to a support, and not held, as it may be, in the hand.

One of the circles is of aluminium, and is borne by a compass-needle; it gives horizontal angles when the instrument is held horizontally. The other is of silvered copper, unequally weighted, and is supported by a delicate axis playing in jewelled holes: it gives vertical circles through the action of gravity when the instrument is held vertically, just as the compass-circle gives azimuthal angles through the action of the magnetic force when the instrument is held horizontally.

The remarkable simplicity and compactness of the Boussole Burnier would make it useful to the traveller, the geologist, and the military engineer. It is the invention of Lieut.-Col. Burnier of the French Engineers, and has been perfected in its details by M. Balbreck, No. 81 Boulevard Mt. Parnasse, Paris.

European Weather-Charts for December 1861. By F. GALTON, F.R.S., F.R.G.S. The author submitted for examination a series of printed and stereotyped charts, compiled by himself, that contained the usual meteorological observations made at eighty stations in Europe, on the morning, afternoon, and evening of each day of December 1861. They were printed partly in symbols and partly in figures, in such a form that each separate group of observations occupies a small label, whose centre coincides with the geographical position of the station where the observations were made. The amount of cloud is expressed by shaded types, the direction of the wind by an equivalent to an arrow, and its force by a symbolical mark. The temperature of the wet and dry thermometers, and the barometric readings (reduced to zero and sea-level) are given in figures. As the charts had been too recently printed to admit of a thorough examination, and as they were ultimately to appear as a separate publication, the author abstained from other deductions than those that were obvious on inspection. Among these, the enormous range and the simultaneity of the wind-changes, testifying to the remarkable mobility of the air, were exceedingly conspicuous.

On the Distribution of Fog round the Coasts of the British Islands.
By Dr. GLADSTONE, F.R.S.

Certain conclusions on this subject formerly arrived at by the author had been re-examined by means of additional returns from the meteorological journals kept at all the stations belonging to the three general lighthouse authorities in England, Scotland, and Ireland, and some returns lent him by Mr. James Glaisher. These afforded confirmation of the greater uniformity of distribution of fogs over the surface of the sea than on land, of their great prevalency where the south-west wind from the ocean strikes upon high ground, of the comparative infrequency of fog on the coasts of straits or portions of sea nearly surrounded by land, and other points previously noted. The returns also indicated that some years are much more foggy than others in nearly all localities; that the same fog sometimes prevails over a large extent of country; and that the frequency of fog differs very greatly in different months of the year, January, February, or March being on some coasts almost free. A generally accepted means of distinguishing between "fog" and "mist" is a great desideratum.

On a New Barometer used in the last Balloon Ascents.
By J. GLAISHER, F.R.S.

Mr. Glaisher exhibited a mercurial barometer which had been designed and constructed by Messrs. Negretti and Zambra for the purpose of checking the readings of the Gay-Lussac's barometer which had been used in the several late balloon ascents. The correctness of the readings of a Gay-Lussac's barometer at low pressure depended upon the evenness of the tube, and it is difficult to calibrate so large a tube. Messrs. Negretti and Zambra selected a good tube, 6 feet in length, attaching a cistern to its lower end. Mercury was boiled throughout the length of the tube; at the entrance of the cistern was placed a stopcock, by which means any definite quantity of mercury could be allowed to pass from the upper half of the tube into the cistern, and its height in the cistern noted and engraved; then a second portion, and so on. This process could be repeated. When the cistern was thus satisfactorily divided, the tube was cut in two, and to the upper half the cistern was joined; a scale was attached to this portion, and the reverse operation was performed, viz., allowing portions of the mercury to pass from the cistern into the tube, which could be regulated by means of the stopcock, and thus the scale was divided. The process, in fact, is using the tube to graduate itself. In carriage, the stopcock locks the mercury in the tube. This instrument was used, and acted well on the extreme high ascent.

On the Additional Evidence of the Indirect Influence of the Moon over the Temperature of the Air, resulting from the Tabulation of Observations taken at Greenwich in 1861-62. By J. PARK HARRISON, M.A.

The author stated that the additional evidence derived from the observations of mean temperature at Greenwich for the years 1861-62 confirmed the conclusions arrived at from a tabulation of the observations for the forty-seven years previous, viz., that the temperature of the air at the moon's first quarter is higher than it is at full moon and last quarter, and that this is due to the amount of cloud at first quarter being greater on the average than it is at the periods of full moon and last quarter. The difference in the amount of rain also at first quarter in 1861-62 was 2.27 inches more than at full moon, on a mean of eighty-four observations on seven days at each period.

On the Relative Amount of Sunshine falling on the Torrid Zone of the Earth. By Professor HENNESSY, F.R.S.

By the aid of the author's transformations of formulæ given by Poisson, the area of that portion of the equatorial regions of the earth which receives as much sunshine as the rest of the earth's surface is ascertained. This area, at the outer limits of the earth's atmosphere, is thus found to be bounded by parallels situate at distances of 23° 44′ 40′′ at each side of the equator; hence the amount of sunshine falling on

the outer limits of the earth's atmosphere between the tropics is very nearly equal to that which falls on the remaining portions of the earth's surface. If we reflect that, according to Principal Forbes's researches, the amount of heat extinguished by the atmosphere before a given solar ray reaches the earth is more than one-half for inclinations less than 25°, and that for inclinations of 5° only the twentieth part of the heat reaches the ground, we immediately see that the torrid zone of the earth must be far more effective than all the rest of the earth's surface as a recipient of solar heat. It follows, therefore, that the distribution of the absorbing and radiating surfaces within the torrid zone must, upon the whole, exercise a predominating influence in modifying general terrestrial climate.

On the Hurricane near Newark of May 7th, 1862, showing the force of the Hailstones and the violence of the Gale. By E. J. Lowe, F.R.A.S. §e. The hurricane about to be described was accompanied by a thunder-storm, which was more or less spread over the centre of England. On the previous evening there were violent thunder-storms, accompanied in various places with large hailstones and with rose-coloured lightning. The hurricane of the 7th of May was remarkable for its violence near Newark, and for the violence of the thunder-storm which occurred at the same time; it will long be remembered in the neighbourhood on account of the devastation that was caused, for the particularly striking night-like darkness, for the great size and curious forms of the hailstones, and on account of the magnificence of the colour of the lightning. At Highfield House the morning was sultry, with thunder about noon, and again continuously in S. and S.E. at three o'clock. At half-past two the temperature in shade had risen to 73°-6 with a west wind, but the clouds whirling round in all directions, a low current carried broken nimbi rapidly from west, whilst the storm-cloud was approaching in a S.S.E. current. At half-past four o'clock the temperature had fallen to 60° (a descent of 13°-6 in two hours), whilst the wind had risen to half a gale. The thunder, though distant, was frequent. The sky gradually became blacker and blacker, until at five o'clock it was darker than I had ever before seen it except during a total eclipse of the sun. A book with bold type could scarcely be read at a window, nor away from it could the hands of a watch be seen. This storm put on very much the appearance of a total eclipse; near objects had a yellow glare cast upon them, and the landscape was closed in on all sides at the distance of half a mile by a storm-cloud wall. Rain fell in torrents, but not in an ordinary manner; it was swept along the ground in clouds like smoke. Flashes of lightning also came in impulses, four or five following each other in rapid succession, succeeded by a brief pause, and then four or five The colour of the lightning was lovely beyond description, being an intense bluish red-almost rose. The wind now veered to the S.S.E., taking the storm's direction. The temperature had descended to 51° (a fall of more than 2210), and the anemometer showed 9 lbs. pressure on the square foot. Severe as this storm was at Highfield House, it dwindled into insignificance when compared with its violence near Newark. It is scarcely possible to imagine any destruction more complete than that effected by this fearful storm. Fortunately its ravages were confined within narrow limits, being restricted to three miles in length and 150 yards in width, commencing at the village of Barnby; after proceeding a mile its violence considerably increased; before reaching Coddington it tore up the hedges that surrounded the fields and unroofed the farm buildings. At Balderton Lane it threw down farm buildings and uprooted enormous oak-trees; a quarter of a mile further it unroofed the house of Mr. James Thorp's head keeper, the hailstones breaking nearly all the windows, having in many instances been driven through the glass, cutting out smooth holes. The spout of this house, too heavy for one man to lift, was carried 100 yards, and a perfectly sound elm-tree, about 60 feet in height and 5 feet 10 inches in circumference (where broken off), was snapped asunder four feet from the ground, and the tree carried twenty-nine yards through the air. The wood of this tree was twisted to the very heart. Here a man was lifted off the ground and then carried twenty yards, being unable to save himself, finally lodging in a hedge. Thirty or forty yards from Mr. Thorp's house at Beaconfield the hur ricane divided, leaving the house itself intact, and also the trees in its immediate

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neighbourhood, from S. round by E. to N., while on the W. side outbuildings were unroofed or destroyed, the large garden wall thrown down, and the fencing around the plantations broken off and carried into the fallen timber. A few yards beyond the house the gale reunited, and passing through a wood destroyed all the trees; it then proceeded across fields as far as Winthorpe, and here its fury became exhausted. The gale rotated in the direction of W. to S., which was apparent from the twist of the wood of the snapped-off trees, and also from an avenue of chestnuts situated on the extreme eastern edge of the hurricane having all the torn-off boughs lying on the S. or storm-side, and being carried back beyond the level of the trees.

Proposed Measurement of the Temperatures of Active Volcanic Foci to the greatest attainable Depth, and of the Temperature, state of Saturation, and Velocity of Issue of the Steam and Vapours evolved. By ROBErt Mallet, C.E., M.A., F.R.S.

The author having circulated the following document amongst various Members of the British Association a short time prior to the Meeting and during same, enlarged upon the objects of his proposed experimental inquiry; and explained to Section A, in part, the methods he intended to employ.

Determination of Volcanic Temperatures.—It is a singular fact, and one scarcely creditable to the past investigation of volcanic phenomena, that up to this time no careful attempt has been made to determine, even approximately, the temperature of the heated or incandescent focus of any active volcano, even at the mouth of the crater, still less to depths lower down.

Much labour and time have been lavished upon analysation of the gases and solid products evolved, and upon other still more minute inquiries-more than was necessary, indeed, to obtain all the leading information as to the nature of vulcanicity (using that general term to express the train of forces and of events whence the supply of volcanic heat and energy is kept up) which such results are capable of yielding; but the most obvious of all physical data, viz. those referring to the actual temperature of volcanic foci at the greatest attainable depths, have been completely neglected by vulcanologists, either because they too hastily concluded that experimental measurements of such were impossible, or, more probably, because, as often happens in the investigation of nature, the most obvious question is that which is longest neglected being put to nature.

The experiments that have been made on the heat of lava-fissures, and upon the temperatures of geysers, hot-springs, mines, &c., do not of course bear upon those here in point.

It seems almost unnecessary to dilate upon the importance to vulcanology, and to all cosmical physics, of some precise information as to these focal temperatures, the knowledge of which would assign limits at once to many speculations at pre-. sent vague and perhaps valueless, give measure to the estimation of the forces concerned, and direct further investigation as to the sources whence these may be derived.

For brevity, the writer may venture to quote on this subject the following passage from his Report to the Royal Society on the great Neapolitan earthquake of 1857 :"I cannot find that any professed investigator of volcanos has ever thought of making the very obvious and important experiment of lowering, with an iron wire, a pyrometer as far as possible into a crater, in order to get some idea of its actuaĺ temperature, even within a few score yards of its mouth.

"When on Vesuvius, on the occasion of this Report, I feel satisfied that I could have so measured the temperature of the minor mouth-then in powerful action— to the depth of several hundred feet, had I possessed the instrumental means at hand. To this smaller mouth it was then possible, by wrapping the face in a wet cloth, to approach so near upon the hard and sharply-defined (though thin and dangerous) crust of lava through which it had broken, as to see its walls for quite 150 feet down, by estimation. They were glowing hot to the very lips, although constantly evolving a torrent of rushing steam with varying velocity. Accustomed as I have been by profession for years to judge of temperature in large furnaces by the eye, I estimated the temperature of this mouth, by the appearance of its heated 1862.

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