« НазадПродовжити »
Having learnt that a series of pendulum experiments at the prineips stations of the Great Russian Arc were in contemplation, I availed mysel of an opportunity of informing M. Savitsch, by whom the operations wer to be conducted, that the Invariable Pendulums which had been employe in the English experiments were now in the possession of the Royal Society and, being unemployed, would, I was persuaded, be most readily lent b; the Society on an application to that effect being made. The constants o these instruments, including the coefficient in the reduction to a vacuum having been most carefully determined, they were ready, with the clock and stands belonging to them, for immediate use, and would have tin further advantage, that experiments made with them in Russia would b( at once brought into direct connexion with the British series extending from 79° 50' N. to 62° 56', S. latitude. The communication was mosi courteously received and replied to. It appeared, however, that a detachec invariable pendulum had been already ordered by the Russian Government from M. Repsold, of Hamburg, shorter than the English pendulums foi convenience in land transport, and with two knife-edges and two fixed lenses, symmetrical in size and shape but one light and the other heavy and so arranged that the times of vibration should be the same on eithei knife-edge in air of the same temperature and density. M. Savitsch expressed his desire to bring this pendulum in the first instance to Kew, and to secure thereby the connexion of his own with the English series, where also he would have the opportunity of testing the exactness of the correction for buoyancy by vibrating his pendulum on both its knife-edges in the vacuum-apparatus which is now established at Kew.
It is much to be desired that a similar series of pendulum experiments to those about to be undertaken in Russia should be made at the principal points of the Great Indian Arc; and the steps which are understood to be in progress in providimg new instruments for the verification of the astronomical and geodesical operations of the Trigonometrical Survey of India, and to give them a still greater extension, would seem to present a most favourable opportunity for the combination of pendulum experiments. In such case the pendulums of the Royal Society might be made available with excellent effect.
The large size of our printed volumes in the present year gives no unfavourable and, I think, no unfair idea of the present scientific activity of the Society; for I believe it may be safely said that our Council has not been less vigilant and cautious than heretofore in the selection of the papers to be printed. Although much care has been given to keeping the expenses of illustration within reasonable bounds, the cost of the Society's publications has been this year unusually high; yet I am glad to be able to state that our whole expenditure within the year has fallen within our income. With your permission, I will briefly advert to a few of the subjects which have occupied the Society's attention in the past year.
The researches of Kirchhoff and Bunsen have rendered it in a high degree probable that we shall be able to obtain much insight into the chemical nature of the atmospheres of the brighter fixed stars, by observing the dark lines in their spectra and comparing them with the bright lines in the spectra of elementary, and perhaps also of compound, bodies in the state of incandescent gas or vapour. The interest of such an inquiry is obvious; but the difficulties involved in it are very great. The quantity of light coming from even such a star as Sirius is so small, that without the use of a powerful telescope the spectrum obtained would be too faint to bear sufficient enlargement to 6how properly the fixed lines. The apparent diurnal motion of the stars causes much embarrassment, unless the instrument he mounted equatoreally, and furnished with a clock movement. The control of the experiments on incandescent bodies requires a thorough knowledge of chemistry, so as to avoid being misled by imparities in the substances examined, and to be prepared to interpret decompositions or combinations which may take place under unusual circumstances, and which may be manifested only by their effects. Nor can the astronomical and physical parts of the inquiry be well dissociated, so as to be separately undertaken by different individuals; for the most elaborate drawings can hardly convey a faithful idea of the various aspects of the different dark and bright lines, which yet must be borne in mind in instituting a comparison in cases of apparent coincidence. It is fortunate, therefore, that the inquiry has been taken up by two gentlemen working in concert. In a short paper read to the Society on the 26th of last February, and published in the Proceedings, Mr. Huggius and Dr. Miller have described and figured the spectra of three of the brighter stars; and this part of the inquiry will doubtless be continued. In a paper since presented to the Society, Mr. Huggins describes the means employed for practically determining with accuracy the positions of any stellar lines »hich may be observed, with reference to known points of the spectrum, and has given beautiful maps of the spectra of twenty-four of the elementary bodies under the action of the inductive discharge, reserving others for a future communication. When the inquiry is completed, it is possible that we may obtain an amount of knowledge, respecting the constitution of those distant heavenly bodies, of which we have at present tittle conception.
Professor Tyndall has given us the fourth of a series of papers upon the relation of Gases and Vapours to Radiant Heat. In the course of these inquiries, he has shown that the different aeriform bodies, even though colourless, exert very different degrees of absorptive action on the rays of heat,—- and that certain portions of these heat-rays, are more powerfully absorbed than others—rays from objects at a low temperature being more easily absorbed than those from objects at an elevated temperature. He has also proved that gases radiate as well as absorb, and, in conformity with what is known in the case of solids, that in gaseous media also there is equality in the powers of radiation and absorption. Bodies which exert an absorbent effect in the liquid form preserve it in the gaseous state. It further experiments should confirm Prof. Tyndall's views upon the absorptive action of aqueous vapour upon radiant heat of low intensity, these results must materially modify some of the views hitherto held upon the meteorological relations of aqueous vapour.
The Bakerian Lecture, by Mr. Sorby, is entitled by him "On the Direct Correlation of Mechanical' and Chemical Forces." In this paper are embodied a series of observations upon the influence of pressure upon the solubility of salts, in which he has obtained results analogous to the changes observed in the freezing-point of liquids under pressure. He finds, in cases where, as is usual, the volume of the water and the salt is lets than the volume of the water and the salt separately, that the solubility is increased by pressure, but that, in cases where (as when sal-ammoniac is dissolved in water) the bulk of the solution is greater than that of the water and salt taken separately, the solubility is lessened by a small but measurable amount. On the contrary, salts which expand in crystallizing from solution must, under pressure, overcome mechanical resistance in that change; and as this resistance is opposed to the force of crystallization, the salt is rendered more soluble. The extent of the influence of pressure, and the mechanical value of the force of crystalline polarity, were found to vary in different salts. Mr. Sorby also indicates the results of the action of salts upon certain carbonates under pressure, and purposes pursuing his researches upon chemical action under pressure. This paper may therefore be regarded as the first of a series upon a highly interesting and important branch of investigation, for which Mr. Sorby appears to be specially fitted, from his combining the needful geological knowledge with the skill in manipulation required in the physical and chemical part of the inquiry.
The examination of the bright lines in the spectra of electric discharges passing through various gases, and between electrodes of various metals, has of late years attracted very general attention. Each elementary gas and each metal shows certain well-marked characteristic lines, from the presence or absence of which it is commonly assumed that the presence or absence of the element in question may be inferred. But the question may fairly be asked, Has it been established that these lines depend so absolutely on chemical character that none of them can be common to two or more different bodies? Has it been ascertained that, while the chemical nature of the bodies remains unchanged, the lines never vary if the circumstances of mass, density, &c. are changed? What evidence have we that spectra are superposed, so that we observe the full sum of the spectra which the electrodes and the medium would produce separately 1
To examine these and similar questions in the only unimpeachable way
(that of actual experiment) formed the object of a long and laborious research by Dr. Robinson, the results of which are contained in a paper in oar Transactions. In the course of this research, Dr. Robinson had occasion to take careful measures of the positions of all the bright lines j>ible (and not too weak to measure) in a great number of spectra—those, namely, of the induction discharge passing between electrodes of twenty liferent metals, as well as graphite, most of which were observed in each of fire different gases (including air), and for each gas separately at the atmospheric pressure and at the low pressure obtained by a good air-pump.
On taking an impartial survey of this great assemblage of experimental facts, Dr. Robinson inclines to the opinion that the origin of the lines is to be referred to some yet undiscovered relation between matter in general and the transfer of electric action; and that while the places of the lines ire thus determined independently of particular circumstances, the brightneu of the lines is modified, according to the special properties of the molecules which are present, through a range from great intensity down to a faintness which may elude our most powerful means of observation.
By a discussion of the results of the magnetic observations maintained for several years past at the Kew Observatory with an accuracy previously ■'[■attained, and by combining these with the earlier results of the observations at the British colonial observatories,I have been enabled to trace and, as I believe, satisfactorily to establish the existence of an annual variation in the three elements of the earth's magnetism, which has every appearance of being dependent upon the earth's position in her orbit relatively to the sun. Substantiated by the concurrent testimony of observations in both hemispheres, and in parts of the globe most widely distant from each other, this conclusion furnishes an additional evidence of a cosmical magnetic relation subsisting between the earth and other bodies of the solar system, and thus extends the scope and widens the basis of sound induction upon which the permanent relations of magnetical science must rest.
To Dr. Otto Torell, Professor of Zoology in the University of Lund, we we indebted for a communication of much interest, informing us of the progress made by an expedition appointed by the Swedish Government at the recommendation of the Royal Academy of Sciences at Stockholm, to siecute a survey preliminary to the measurement of an arc of the meridian *t Spitzbergen. The objects of the preliminary survey were to ascertain whether suitable angular points for a triangulatiou could be found from Ross Island at the extreme north, to Hope Island at the extreme south of Spitzbergen, and to determine on a favourable locality for the measurement of a base-line. The result of the first year's exploration has been the selection of stations, on hills of moderate height and easy access from the coast, for nine triangles shown in the sketch accompanying Dr. Torell's paper, including Ross Island in the extreme north, and extending over about 1° 50' of the proposed arc of 4-\- degrees. A convenient Iocs lity has also been found for the base-line. The continuation of the preli minary survey to the extreme southern limit is to be the work of th summer of 1864. The report of the Geodesioal Surveyors has shown the the northern portion presents no impediments which may not be sui mounted by courage and perseverance; and with regard to the souther portion, the knowledge already acquired is considered to justify the ex pectation that the result of the second year's exploration will be no les favourable. Should such be the case, it is anticipated that the necessar steps will be taken for carrying into execution the measurement of the nn itself.
I may perhaps be permitted to allude for a moment to the peculiar in terest with which I must naturally regard the proposed undertaking. Th< measurement of an arc of the meridian at Spitzbergcn is an enterpris< which nearly forty years ago was a cherished project of my own, which ] had planned the means of executing, and which I ardently desired to b< permitted to carry out personally. I may well therefore feel a peculi&i pleasure in now seeing it renewed under what I regard as yet mon promising auspices,—whilst I cannot but be sensible of how little I could have anticipated that I should have had the opportunity, at this distance of time, and from this honourable chair, of congratulating the Swedish Government and Academy upon their undertaking, and of thanking Dr, Torell for having traced its origination to my early proposition.
It is well remarked by Dr. Torell, that the triangulation, should it be proceeded with, will not be the only result of the years of scientific labour at Spitzbergen. There arc, indeed, many important investigations for which the geographical circumstances would be eminently favourable. Two such may be specified, for which we may reasonably anticipate that full opportunity would be afforded, and for which the requisite instruments of precision are neither costly nor cumbersome. One is a more exact determination of the data on which our Tables of Astronomical Refraction are founded. The other is the employment of Cagnoli's method for determining the figure of the earth by occultations of the fixed stars*. This last would be tried under circumstances far more favourable than those contemplated by its original proposer, by reason of the high latitude of the northern observer—the greater number of stars in the moon's path, now included in our catalogues, of which a special ephemeris might be made —and the much greater amount of concerted corresponding observations which might now be secured. The advantage peculiar to this mode of determination is, that it is exempt from the influence of local irregularities in the direction and force of gravity which embarrass the results of
* Antonio Cagnoli, " Nuovo e siouro mezzo per riconoscere la Figura della Terra," Memoric della Societa Italiana, Verona, vol. vi. 1792.
An English translation, with Notes and an Appendix, was printed for private circulation in 1819, by Mr. Francis Baily.