382 



NATURE 



[August 20, 1891 



opened when, in 1880, Dr. Henry Draper obtained a picture 

 of the nehula of Orion ; but a more important advance was 

 made in 1883, when Dr. Common, by his photographs, brought 

 to our knowledge details and extensions of this nebula hitherto 

 unknown. A further disclosure took place in 1885, when the 

 Brothers Henry showed for the first time in great detail the 

 spiral nebulosity issuing from the bright star Maia of the 

 Pleiades, and, shortly afterwards, nebulous streams about the 

 other stars of this group. In 1886, Mr. Roberts, by means of 

 a photograph to which three hours' exposure had been given, 

 showed the whole background of this group to be nebulous. 

 In the following year Mr. Roberts more than doubled for us the 

 great extension of the nebular region which surrounds the trape- 

 zium in the constellation of Orion. By his photographs of the 

 great nebula in Andromeda he has shown the true significance 

 of the dark canals which had been seen by the eye. They are 

 in reality spaces between successive rings of bright matter, 

 which appeared nearly straight owing to the inclination in which 

 they lie relatively to us. These bright rings surround an unde- 

 fined central luminous mass. I have already spoken of this 

 photograph. 



Some recent photographs by Mr. Russell show that the great 

 rift in the Milky Way in Argus, which to the e)e is void of 

 stars, is in reality uniformly covered with them. Also, quite 

 recently, Mr. George Hale has photographed the prominences 

 by means of a grating, making use of the lines H and K. 



The heavens are richly but very irregularly inwrought with 

 stars, the brighter stars cluster into well-known groups upon a 

 background formed of an enlacement of streams and convoluted 

 windings and intertwined spirals of fainter stars, which becomes 

 richer and more intricate in the irregularly rifted zone of the 

 Milky Way. 



We, who form part of the emblazonry, can only see the design 

 distorted and confused ; here crowded, there scattered, at 

 another place superposed. The groupings due to our position 

 are mixed up with those which are real. 



Can we suppose that each luminous point has no relation to 

 the others near it than the accidental neighbourship of grains of 

 sand upon the shore, or of particles of tbe wind-blown dust of 

 the desert ? Surely every star, from Sirius and Vega down to 

 each grain of the light-dust of the Milky Way, has its present 

 place in the heavenly pattern from the slow evolving of its past. 

 We see a system of systems, for the broad features of clusters 

 and streams and spiral windings which mark the general design 

 are reproduced in every part. The whole is in motion, each 

 point shifting its position by miles every second, though from the 

 -august magnitude of their distances from us and from each other, 

 it is only by the accumulated movements of years or of genera- 

 tions that some small changes of relative position reveal 

 themselves. 



The deciphering of this wonderfully intricate constitution of 

 the heavens will be undoubtedly one of tbe chief astronomical 

 works of the coming century. The primary task of the sun's 

 motion in space, together with the motions of the brighter 

 stars, has been already put well within our reach by the spec- 

 troscopic method of the measurement of star-motions in the line 

 of sight. 



From other directions information is accumulating : from 

 photographs of clusters and parts of the Milky Way, by Roberts 

 in this country, Barnard at the Lick Observatory, and Russell at 

 Sydney ; from the counting of stars, and the detection of their 

 configurations, by Holden and by Backhouse ; from the map- 

 ping of the Milky Way by eye, at Parsonstown ; from photo- 

 graphs of the spectra of stars, by Pickering at Harvard and 

 in Peru ; and from the exact portraiture of the heavens in the 

 great international star chart which begins this year. 



I have but touched some only of the problems of the newer 

 side of astronomy. There are many others which would claim 

 our attention if time permitted. The researches of the Earl of 

 Rosse on lunar radiation, and the work on the sam.e subject and 

 on the sun, by Langley. Observations of lunar heat with an 

 instrument of his own invention by Mr. Boys ; and observations 

 of the variation of the moon's heat with its phase by Mr. Frank 

 Very. The discovery of the ultra-violet part of the hydrogen 

 spectrum, not in the laboratory, but from the stars. The con- 

 firmation of this spectrum by terrestrial hydrogen in part by H. 

 W. Vogel, and in its all but complete form by Cornu, who 

 found similar series in the ultra-violet spectra of aluminium and 

 thallium. The discovery of a simple formula for the hydrogen 



NO. II 38, VOL. 44] 



series by Balmer. The important question as to the numerical 

 spectral relationship of different substances, especially in connec- 

 tion with their chemical properties ; and the further question as 

 to the origin of the harmonic and other relations between the 

 lines and the groupings of lines of spectra ; on these points con- 

 tributions during the past year have been made by Rudolf v. 

 Kovesligethy, Ames, Hartley, Deslandres, Rydberg, Griinwald, 

 Kayser and Runge, Johnstone Stoney, and others. The remark- 

 able employment of interference phenomena by Prof. Michelson 

 for the determination of the size, and distribution of light within 

 them, of the images of objects which when viewed in a telescope 

 subtend an angle less than that subtended by the light-wave at a 

 distance equal to the diameter of the objective. A method 

 applicable not alone to celestial objects, but also to spectral 

 lines, and other questions of molecular physics. 



Along the older lines there has not been less activity ; by 

 newer methods, by the aid of larger or more accurately con- 

 structed instruments, by greater refinement of analysis, knowledge 

 has been increased, especially in precision and minute exactness. 



Astronomy, the oldest of the sciences, has more than renewed 

 her youth. At no time in the past has she been so bright with 

 unbounded aspirations and hopes. Never were her temples so 

 numerous, nor the crowd of her votaries so great. The British 

 Astronomical Association formed within the year numbers 

 already about 600 members. Happy is the lot of those who are 

 still on the eastern side of life's meridian ! 



Already, alas ! the original founders of the newer methods are 

 falling out — Kirchhoflf, Angstrom, D' Arrest, Secchi, Draper, 

 Becquerel ; but their places are more than filled ; the pace of the 

 race is gaining, but the goal is not and never will be in sight. 



Since the time of Newton our knowledge of the phenomena 

 of Nature has wonderfully increased, but man asks, perhaps 

 more earnestly now than in his days. What is the ultimate reality 

 behind the reality of the perceptions ? Are they only the 

 pebbles of the beach with which we have been playing ? Does 

 not the ocean of ultimate reality and truth lie beyond ? 



SECTION A. 



MATHEMATICS AND PHYSICS. 



Opening Address by Prof. Oliver J. Lodge, D.Sc, 

 LL.D., F.R.S., President of the Section. 



During the past year three or four events call for special 

 mention in an annual deliverance of this kind by a physicist. 



One is the Faraday centenary, which was kept in a happy and 

 simple manner by a cosmopolitan gathering in the place so long 

 associated with his work, and by discourses calling attention to 

 the modern development of discoveries made by him. 



Another is the decease of the veteran Wilhelm Weber, one of 

 the originators of that absolute system of measurement which, 

 though still ungrasped in its simplicity and completeness by the 

 majority of men engaged in practice, nor even, I fear, wholly 

 understood by some of those engaged in University teaching, has 

 yet done so much, and is destined to do |still more, for the uni- 

 fication of physical science, and for a thorough comprehension 

 of its range and its limitations. 



A third event of importance during the year is the discovery 

 in America of a binary system of stars, revolving round each 

 other with grotesque haste, and with a proximity to each other 

 such as to render their ordinary optical separation quite impos- 

 sible. Ideas concerning the future of such systems, if, as seems 

 probable, their revolution period is shorter than their axial period, 

 will readily suggest themselves, in accordance with the principles 

 elaborated by Prof. George Darwin. The subject more properly 

 belongs to our President, but I may parenthetically exclaim at 

 the singular absurdity of the notion which was once propounded 

 by a philosopher, that motion of stars in our line of sight nmst 

 for ever remain unknown to us ; when the mere time of 

 revolution of a satellite, compared with its distance from its 

 central body, is theoretically sufficient to give us infor- 

 mation on this head. As a matter of pedagogy it is 

 convenient to observe that the principle called Doppler's, 

 which is generally known to apply to the periodic disturbances 

 called Light and Sound, applies equally to all periodic occur- 

 rences ; and that the explanation of anomalies of Jupiter's first 

 satellite by Roemer may be regarded as an instance of Doppler's 



