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Extracts, relating to the Observatory at Kew, from a Report presented to the Portuguese Government by Dr. Jacintho Antonio De Souza, Professor of the Faculty of Philosophy in the University of Coimbra. Communicated by J. P. Gassiot, F.R.S.
[Ordered to be printed among the Eeporta.]
Dr. JAcnfrao Aittohio Be Souza has published an account of a visit in 1860 to the Scientific Establishments of Madrid, Paris, Brussels, Greenwich, and Kew, and of a second visit in 1861 to the Obsorvatory of Kew, both visits having been made by the desire of his Government, and having for their principal object to obtain information preparatory to the establishment of a Magnetical and Meteorological Observatory at the University of Coimbra.
His first visit was to Madrid, where he states that he found nothing doing in magnetism; and that in meteorology the only instrument presenting any novelty was the ingenious and comprehensive meteorograph of Padre Secchi, intended to register atmospheric pressure, the amount of rain, and the direction and velocity of the wind. Prof, do Souza commends this instrument for the small space which it occupies, but adds that some of its indications, particularly those of temperature, appeared to him to be subject to much uncertainty. He was disposed to attribute the absence of any magnetical investigations at Madrid rather to tho indifference of the Government than to any want of zeal on the part of the distinguished Director, Don Antonio Aguilar, of whose kind reception ho also speaks gratefully.
He next proceeded to Paris, where he arrived on the 15th of August, "the birthday of the first Napoleon," and was dazzled with the splendour of all that met his eyes in the general aspect of that brilliant capital. He had looked forward to finding in "the Imperial Obsorvatory directed by Le Verrier," besides a " typical Astronomical Observatory," one of the best in " magnetism and meteorology, where there would be much to see and to study; " but after obtaining access to that fine establishment, "not without difficulty and loss of precious time," he derived, as he states, "little interest and profit from the hasty view which M. Le Verrier afforded him of the Astronomical Observatory (which is indeed excellent)," whilst, in regard to the special objects of bis journey, though MM. Desains and Charault courteously showed him whatever could be said to appertain to magnetism or meteorology, he states that he " came away disappointed."
At Brussels he refers gratefully to the frank and delicate kindness with which, on presenting himself at the Observatory, he was received by M. Quetelet, and expresses his admiration of what that philosopher had accomplished with means from which very few others could have educed similar results, and of the impulse imparted by him to the advancement of the "physique du globe," Baying at the same time that, without this knowledge, the inspection of the magnetical and meteorological portion of the Observatory would lead a visitor to regard it as not being at the present time in a state of prosperity.
Approaching London by the Thames, and entering "the vast cupola of smoke which covers that great capital," he seems to have been powerfully impressed by the dissimilarity to what he had previously seen in France and Belgium; and by the grandeur as well as the sombre character of the spectacle presented to his view.
On arriving at Greenwich he was courteously received at the Royal Observatory, admired the general arrangements of that great establishment, and inspected minutely the magnetical and meteorological portion, with the « advantage of verbal explanations by the Eev. Robert Main, who was the'fe at the ■ moment, besides the written explanations kindly given to him by Mr. Airy." He thus became well acquainted with the localities, arrangements, and instruments, of which he gives a detailed description; but as he ultimately preferred ordering^for his own Observatory instruments on the pattern of those employed at Kew, we may pass at once to his account of that establishn>ent,which will be given nearly in his awn word*:—
"The Observatory at Kew, besides occupying itself with meteorological and .magnetical.phenomena, and tho photographic registry of the spots of the sun, verifies meteorological and magnetical instruments, compares them with the excellent patterns which it possesses, determines their constants, and improves the methods of observation. The Director (Mr. Balfour Stewart) was absent; but Mr. Chambers, assistant observer, and Mr. Beckley, mechanical engineer of the Observatory, attended me so obligingly, and with such sincere desire to satisfy all my importunate inquiries, that I derived great profit from the visit.
"The self-registering magnetic instruments at Kew were constructed in ,1857, about ten years after the registering apparatus at Greenwich was adapted to the previously existing instruments at that Observatory. Based on the same general principles, they differ in size, and in certain happy innovations introduced by Mr. Welsh and executed by Adie (a skilful artist in London). They have been in action since 1858, and give results which leave nothing to be desired.
: "The locality in which the self-registering magnetic instruments are placed at Kew is in the basement-story of the building, which was formerly an astronomical observatory: tho choice was determined by a condition which should never be lost sight of, viz. the greatest attainable constancy of temperature."
[Having already described the magnetographs at Greenwich, Prof, de Souza, whilst giving a very elaborate description of the Kew instruments, dwells at length principally on the points in which they differ from those at Greenwich; but the description is here omitted, as the Kew instruments have been carefully and well described by Mr. Balfour Stewart in the volume of Beporta of the Aberdeen Meeting of the British Association, p. 200-228. Prof, do Souza proceeds as follows:—]
"A short time before my visit to the Observatory Dr. Bergsma had been there, sent by the Dutch Government to examine the magnetographs destined for an observatory in Java, and constructed on the Kew pattern-. I may say in passing that this examination consists in receiving practical instruction on the modo of manipulating with tho instruments, in assisting in their collocation in the verification-house, and in the determination of constants. Somo modifications were introduced in Dr. Bergsma's magneto^ graphs which I will now notice, and which constitute their last state of improvement.
"The great bell-glasses which rest on the marble disks were replaced by cylinders of gun-metal surmounted by smaller glass cylinders. Each has an aperture to which is adapted a plate of glass with parallel faces, taking the place which in the great bell-glasses was occupied by the openings of the glass plato and of the achromatic lens; by this new arrangement the achromatic lens is independent of the cylinder, and can be brought near to, or removed further from, the mirror according to convenience. In this manner any disarrangement of the cylindrical glasses, or the taking of them away; does not alter the position of tho lens, or interrupt the march of the magnetoi graphs. These different pieces fit so as to enclose the magnet hermetically; and thus the air can be rarefied or withdrawn by means of an air-pump in communication with a tube which passes through the marble disk and opens into the enclosure. This exhaustion of the air preYonts the influence upon the magnets of currents of air. • .: .
"Three telescopes, directed to the mirrors of the magnetographs, are established on two Btone pillars, and have each an ivory scale the divisions of which are reflected, by the moveable and by the fixed mirror, into the interiot of the telescope, offering in the field of view two very distinct images of the scale, one of which moves with the mirror of the magnet, so that at different times different divisions of this scale will appear to coincide with the vertical •Wire of the telescope. By the comparison of these divisions with that of the image which is fixed, the position of the magnet at any moment may be known; so that, besides the continuous photographic record going on out of sight, and only taken account of every other day, there may be obtained, on any occasion, direct observations, which is a consideration of great importance. For example, if there is a magnetic disturbance, not only can it be observed at the instant of its occurrence, but also direct observations may be obtained of oscillations which by their amplitude exceed the limits of the photographic paper. . •
"In describing the magnetographs at Greenwich two scales were mentioned, one elastic, the other of paper, with which the times corresponding to the different points of the base-line were obtained, and the values of the ordinate* of the curves calculated. These scales at Kew are metallic, and make part of an apparatus very simple and ingenious, which, being subject to a graduated movement, is both easy and exact in operation. It is, however, not easily described without the assistance of a figure.
'.' For absolute determinations and secular changes there is a detached building of wood (copper-fastened) at a distance from the Obsorvatory, where there aro three wooden pillars solidly fixed in the ground, one for the instruments with which the coefficients of temperature and of induction of the magnetic bars are determined, and two for the inclinometer of Barrow and the unifllar of Gibson. These two instruments and a good chronometer constitute the necessary furniture of this building."
After a very careful and detailed description of the inclinometer and unifllar, Prof, de Souza proceeds, in his account of his first visit to Kew, as follows;—
"In the verification-house, sixty yards from the observatory, Mr. Beckley was setting up for trial for the first time the registering electrometer of Professor Thomson of Glasgow. This new invention, which seems destined to supply a great desideratum in meteorology, would have been one of the objects of the greatest interest to me, if I could have seen it in action and have appreciated some of its results. Dispersed as were its different parts, I coidd not well make to myself a clear idea of the whole. The following is what I gathered from the explanations of Mr. Beckley. ■:
"Professor Thomson's electrometer has for its object the photographic registration, by the system of Brooke, of variations in the difference between the electric tension of the atmosphere and of the earth. A semicircle of brass communicates with tho earth; anothor semicircle of the same metal is insulated from the earth, and is in communication with the. external air by means of the water of a reservoir, which is thrown into the air in a constant jet. From the top of the discontiruous circle formed by these semicircles, and in the direction of tho spaco which they leave between them, there is suspended a metallic needle insulated from the wholo of the apparatus, but in communication with a Leyden jar, to which is given a constant charge measured by the angle of torsion made by another needle suspended to the thread of another apparatus. With the first needle there moves a small mirror, on which falls the light of a lamp reflecting upon the registering cylinder whore the electric curve is produced upon sensitive paper. Another fascicle of light which comes from the fixed mirror gives the baseline. One of the semicircles being in the state of the earth's, and the other in that of the atmosphere's electric tension, and the needle which moves at the top of the space which separates them having a known and constant electricity, it is clear that the slightest alteration in the difference between the tensions, or in the quality of the electricity by which they arc produced, will be directly indicated by the movement of the needle which impresses itself immediately on the photographic paper. If this instrument receives at Kew the attention of which inventions conducing to the advancement of science are there thought worthy, and if any imperfections which may be discovered in it in practice are successfully removed, Professor Thomson will have the honour of having discovered the most sensitive and instantaneous electrometer in existence, which will doubtless smooth the great difficulties which impede the advance of the science of atmospheric electricity. In the presence of this electrometer the electric apparatus employed at Greenwich will fall into disuse, as it has already done at Kew, where it is dismantled. Of the other meteorological instruments in the Kew Observatory, I will only mention the great standard barometer, or rather the process by means of which its large tube is filled. The barometer and a cathetometer, with which are observed the differences of level of the indices of the mercury in the cistern and in the column, are fixed to a wall which formerly supported the mural gradient of the Astronomical Observatory. It is essentially the barometer of Regnault; but it can turn around its axis, which is adjusted in the vertical position by means of screws of pressure: the indices move until they touch the surface of the mercury of tho cistern; one terminates in an edge, the other in a cone: the diameter of the tube is 1*1 inch."
Prof, de Souza here describes in considerable detail the process of making and filling such a barometer-tube. [For this process the English reader is referred to Mr. Welsh's original paper in the Philosophical Transactions for 1856, Art. XXIII.]
Before returning to London, Prof, de Souza visited the Gardens at Kew, and takes occasion to express his very great admiration of the gardens, the palm-house, and especially of the museum. He then proceeds as follows:—
"In London I addressed myself to Major-General Sabine. I have great satisfaction in declaring thus publicly, that the relations acquired with this courteous gentleman so long engaged in magnetical science, constitute one of the most valuable acquisitions which I made in England. It is known that General Sabine has devoted himself for almost half a century, with an ardour and activity never interrupted, to the study of terrestrial magnetism. From 1818 to 1822 he made four successive long scientific voyages; in 1837 he published the first general map of the isodynamic lines of the globe; afterwards he brought about the establishment of four observatories very differently circumstanced in regard to the intensity of the terrestrial magnetic force, and in opposite positions in regard to the magnetical and geographical poles and equators—i. e. tho observatories of Toronto, Hobarton, Cape of Good Hope, and St. Helena. He has also superintended these establishments, and reduced and analysed their observations, from whence have resulted numerous and important publications. He continues himself to observo during a portion of the year, and has almost completed a map of the different magnetic elements over England.
"As was to be hoped, General Sabine heard with lively interest that the establishment of a magnotical and meteorological observatory at Coimbra was in contemplation, and readily offered to help forward the realization of this good idea by directing the construction of tho magnotic and other instruments required, and also undertook that they should be verified and their constants obtained at the Kew Observatory, where I should be enabled to mako practical studies, and receive suitable instruction for their establishment and manipulation,
"General Sabine, speaking of tho University of Coimbra in terms very agreeable to a Portuguese auditor, expressed satisfaction at so good an opportunity of sending to this respectable Academy eleven large volumes of observations analysed by him and published, under his superintendence, by tho English Government. Besides tho observations of the four observatories above mentioned, there are also contained in these volumes observations from Lake Athabasca, Fort Simpson, Fort Carlton, Fort Confidence, the Falkland Islands, and Pckin.
"I informed the Faculty at their first meeting after my arrival at Coimbra of the courtesies received from this savant, and I presented to your Excellency at tho proper time the books of which I was the bearer."
Prof.deSouza then proceeds toconsiderthe results of his journey,and its bearing on the establishment of his own hoped-for observatory. Having obtained permission to employ the funds available in the current year in the purchase of magnetic instruments, he wrote to General Sabine, asking him to bespeak for him both the self-registering instruments, and thoso for absolute determinations (as will be specified in the sequel), with any further improvements that he might deem desirable. He had previously consulted General Sabino on an important question, that of the choice between the different dimensions of the magnets in use at Greenwich and at Kew, and says that "the instructive reflections so obtained" had left him "completely satisfied in determining for the Kew dimensions."
In regard to the locality, it appears that the University of Coimbra does not possess any building suitable and available for the purpose; but tho Hector pointed out a site which appeared to M. do Souza highly suitable, if he could assure himself that the ferruginous particles contained in the new red sandstone rock would not bo objectionable. He sent specimens of the rock (a wellknown one in England) through the Portuguese Ambassador to London, and experiments made with them discovered no sensible magnetic action. But although this doubt was thus satisfactorily removed, unfortunately the site in question is private property, and means are wanting both for its purchase and for tho building. He presses on the authorities the urgency of this provision being made without further delay, and states that the plan proposed, after full consultations, and for which Sir. Beckley has offered to make the drawings, combines the greatest economy with all that can be desired scientifically. Finally, ho discusses the question of meteorological instruments, and concludes for obtaining them also from England, proposing to devote to this purpose the means at his disposal up to the termination of tho University year in 18G2.
Second Visit to the Kew Observatory.
Hearing on tho 5th of July (1861) from General Sabine that the magnetic 1862." i