470 



NATURE 



[September 13. 1900 



SECTION A. 



DEPARTMENT OF ASTRONOMY. 



Opening Address by Dr. A. A. Common, F.R.S., F.R. AS., 

 Chairman of the Department. 

 It has been decided to form a Department of Astronomy 

 under Section A, and I have been requested to give an address 

 on the occasion. In looking up the records of the British Asso- 

 ciation to see what position Astronomy has occupied, I was 

 delighted to find, in the very first volume, "A Report on the 

 Progress of Astronomy during the Present Century," made by 

 the late Sir George Airy, so many years our Astronomer Royal, 

 and at that time Plumian Professor of Astronomy at Cambridge. 

 This report, made at the second meeting of the Association, de- 

 scribes, in a most interesting manner, the progress that was 

 made during the first third of the century, and we can gather 

 from it the state of astronomical matters at that time. The 

 thought naturally occurred to me to give a report, on the same 

 lines, to the end of this century, but a little consideration showed 

 that it was impossible in the limited time at my disposal to give 

 more than a bare outline of the progress made. 



At the time this report was written we may say, in a general 

 way, that the astronomy of that day concerned itself with the 

 position of the heavenly bodies only, and, except for the greater 

 precision of observation resulting from better instruments and 

 the larger number of observatories at work, this, the gravita- 

 tional side of astronomy, remains much as it was in Airy's 

 time. 



What has been aptly called the New or Physical Astronomy 

 did not then exist. I propose to briefly compare the state of 

 things then existing with the present state of the science, without 

 dealing very particularly with the various causes operating to 

 produce the change ; to allude briefly to the new astronomy ; and 

 to speak rather fully about astronomical instruments generally, 

 and of the lines on which it is most probable future develop- 

 ments will be made. 



In this report (Brit. Assoc. Report, 1831-32, p. 125) we find 

 that at the beginning of the century the Greenwich Observatory 

 was the only one in which observations were made on a regular 

 system. The thirty-six stars selected by Dr. Maskelyne, and 

 the sun and moon, were observed on the meridian with great 

 regularity, the planets very rarely and only at particular parts of 

 their orbits ; small stars, or stars not included in the thirty-six, 

 were seldom observed. 



This state of affairs was no doubt greatly improved at the 

 epoch of the report, but it contrasts strongly with the present 

 work at Greenwich, where 5000 stars were observed in 1899, in 

 addition to the astrographic, spectroscopic, magnetic, meteoro- 

 logical, and other work. 



Many observatories, of great importance since, were about 

 that time founded, those at Cambridge, Cape of Good Hope 

 and Paramatta having just been started. A list is given of the 

 public observatories then existing, with the remark that the 

 author is "unaware that there is any public observatory in 

 America, though there are," he says, "some able observers." 



The progress made since then is truly remarkable. The first 

 public observatory in America was founded about the middle of 

 the century, and now public and private observatories number 

 about 150, while the instrumental equipment is in many cases 

 superior to that of any other country. The prophetic opinion 

 of Airy about American observers has been fully borne out. 

 The discovery of two satellites to Mars by Hall in 1877, of a 

 fifth satellite to Jupiter by Barnard in 1892, and the discovery 

 of Hyperion by Bond, simultaneously with Lassell, in 1848, are 

 notable achievements. 



The enormous amount of work turned out by the Harvard 

 Observatory and its branches in South America, all the photo- 

 graphic and spectroscopic work carried out by many different 

 astronomers, and the new lines of research initiated show an 

 amount of enthusiasm not excelled by any other country. A 

 greater portion of the astronomical work in America has been 

 on the lines of the new astronomy, but the old astronomy has 

 not been at all neglected. In this branch pace has been kept 

 with other countries. 



From this report we gather that the mural quadrant at most 

 of the observatories was about to be replaced by the divided 

 circle. Trough ton had perfected a method of dividing circles, 

 which, as the author says, ' ' may be considered as the greatest 

 improvement ever made in the art of instrument making." 

 Two refractors of 11 and 12 inches aperture had just been 



NO. 161 I, VOL. 62] 



imported into this country ; clockwork for driving had been 

 applied to the Dorpat and Paris equatorials, but the author had 

 not seen either in a state of action. 



The method of mounting instruments adopted by the Germans 

 was rather severely criticised by the author, the general principle 

 of their mounting being "telescopes are always supported at 

 the middle, not at the ends." 



" Every part is, if possible, supported by counterpoises." 

 "To these principles everything is sacrificed. For instance, 

 in an equatorial the polar axis is to be supported in the middle 

 by a counterpoise. This not only makes the instrument weak 

 (as the axis must be single), but also introduces some incon- 

 venience into the use of it. The telescope is on one side of the 

 axis ; on the other side is a counterpoise. Each end of the 

 telescope has a counterpoise. A telescope thus mounted must, 

 I should think, be very liable to tremor. If a person who is 

 no mechanic and who has not used one of these instruments 

 may presume to give an opinion, I should say that the Germans 

 have made no improvement in instruments except in the excel- 

 lence of the workmanship." 



I have no doubt that this question had often occupied Airy's 

 mind, for in the Northumberland Equatorial Telescope which 

 he designed shortly after for Cambridge he adopted what has 

 been called the English form of mounting, where the telescope 

 is supported by a pivot .at each side, and a long polar axis is 

 supported at each end. This telescope is in working order at 

 the present time at Cambridge. 



When he became Astronomer Royal he used the same design 

 for what was for many years the great equatorial at Greenwich, 

 though the wooden uprights forming the polar axis were in the 

 Greenwich telescope replaced by iron. It says much for the 

 excellence of the design and workmanship of this mounting, 

 designed as it was for an object-glass of about 13 inches 

 diameter, when we find the present Astronomer Royal, Mr. 

 Christie, has used it to carry a telescope of 28 inches aperture, 

 and that it does this perfectly. 



Notwithstanding the greater steadine.ss of the English forn> 

 of mounting, the German form has been adopted generally for 

 the mounting of the large refractors recently made. 



There is much interesting matter in this report of an historical 

 character. 



As I have already said, the new astronomy, as we know it, 

 did not exist ; but in a report [Brit. Assoc. Report, 1831-32, 

 p. 308) on optics, in the same volume, by Sir David Brewster, 

 we find that spectrum analysis was then occupying attention, 

 and the last paragraph of this report is well worth quoting : 

 " But whatever hypothesis be destined to embrace and explain 

 this class of phenomena, the fact which I have mentioned opens 

 an extensive field of inquiry. By the aid of the gaseous absor- 

 bent we may study with the minutest accuracy the action of the 

 elements of material bodies in all their variety of combinations, 

 upon definite and easily recognised rays of light, and we may 

 discover curious analogies between their affinities and those 

 which produce the fixed lines in the spectra of the stars. The 

 apparatus, however, which is requisite to carry on such inquiries 

 with success cannot be procured by individuals, and cannot ever> 

 be used in ordinary apartments. Lenses of large diameter, ac- 

 curate heliostats, and telescopes of large aperture are absolutely 

 necessary for this purpose ; but with such auxiliaries it would be 

 easy to construct optical combinations, by which the defective 

 rays in the spectra of all the fixed stars down to the tenth mag- 

 nitude might be observed, and by which we might study the 

 effects of the very combustion which lights up the suns of other 

 systems." 



Brewster's words are almost prophetic, and it would almost 

 appear as if he unknowingly held the key to the elucidation of 

 the spectrum lines, for it was not until 1859 that Kirchhoff's 

 discovery of the true origin of the dark lines was made. 



Fraunhofer was the first to observe the spectra of the planets- 

 and the stars, and to notice the different types of stellar spectra. 

 In 181 7 he recorded the spectrum of Venus and Sirius, and later, 

 in 1823, he described the spectrum of Mars ; also Castor, 

 Pollux, Capella, Betelgeux and Procyon. 



Fraunhofer, Lamont, Donati, Brewster, Stokes, Gladstone 

 and others carried on their researches at a time when the prin- 

 ciples of spectrum analysis were unknown, but immediately upon 

 Kirchhoft's discovery great interest was awakened. 



With spectrum analysis thus established, aided as it was later 

 by the greater development of photography, the new astronomy 

 was firmly established. 



