r 



ADDRESS. 13 



element are due to the existence of the element in different molecular 

 forms — allotropic or otherwise — at diffei-ent temperatures. 



But great as have been the advances of terrestrial chemistry through 

 its assistance, the most stupendous advance which we owe to the spectro- 

 scope lies in the celestial direction. 



Astronomy. 



At the third meeting of the Association, at Cambridge, in 1833, Dr. 

 Whewell said that astronomy is not only the queen of science, but the 

 only perfect science, which was ' in so elevated a state of flourishing 

 maturity that all that remained was to determine with the extreme of 

 accuracy the consequences of its rules by the profoundest combinations of 

 mathematics ; the magnitude of its data by the minutest scrupulousness 

 of observation.' But in the previous year, Airy, in his report to 

 the Association on the progress of Astronomy, had pointed out that 

 the observations of the planet Uranus could not be united in one 

 elliptic orbit ; a remark which turned the attention of Adams to the 

 discovery of Neptune. 



In his report on the recent progress of Optics, Brewster in 1832 

 suggested that with the assistance of adequate instruments ' it would be 

 possible to study the action of the elements of material bodies upon rays 

 of artificial light, and thereby to discover the analogies between their 

 affinities and those which produce the fixed lines in the spectra of the 

 stars ; and thus to study the effects of the combustions which light up 

 the suns of other systems.' 



This idea has now been realised. All the stars which shine brightly 

 enough to impress an image of the spectrum upon a photographic plate 

 have been classified on a chemical basis. The close connection between 

 stars and nebulte has been demonstrated ; and while the modern science 

 of thermodynamics has shown that the hypothesis of Kant and Laplace 

 on stellar formation, so far as it assumed a fiery cloud for the beginning, 

 is no longer tenable, but that in all probability it gives the true explana 

 tion of stellar evolution, if for the fiery cloud we substitute cold meteoric 

 particles, as suggested by Waterston ' and by Lord Kelvin ^ at the 

 Liverpool meeting of the British Association in 1854. 



We now know that the spectra of many of the terrestrial elements in 

 the chromosphere of the sun differ from those familiar to us in our labora- 

 tories. We begin to glean the fact thai; the chromospheric spectra are 

 similar to those indicated by the absorption going on in the hottest stars, and 

 Lockyer has not hesitated to affirm that these facts would indicate that in 

 those localities we are in the presence of the actions of temperatures suffi- 



' In Note L on a paper on ' The Physics of Media,' communicated to the Royal 

 Society, December 11, 1815, read March 5, 184G, and published, in 1892, in the 

 2'ransactiof)s, with an introduction by Lord Rayleigh. 



- Brit. Assoc. Report, 1854, Ft. II., pp. 59-GI5; Mathematical and Physical Papers, 

 vol. ii., art. Ixix., p. 40. 



