1863.] 



President'' s Address. 



23 



The researclies 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 iixed stars, by observing the dark 

 lines in their spectra and comparing them with the bright hues 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 show properly the fixed lines. The apparent 

 diurnal motion of the stars causes much embarrassment, unless the 

 instrument be mounted equatoreally, and furnished with a clock move- 

 ment. The control of the experiments on incandescent bodies requires 

 a thorough knowledge of chemistry, so as to avoid being misled by 

 impurities in the substances examined, and to be prepared to interpret de- 

 compositions or combinations which may take place under unusual circum- 

 stances, 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 in- 

 stituting 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. Huggins 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 

 which may be observed, with reference to known points of the spectrum, 

 and has given beautiful maps of the spectra of twenty-four of the ele- 

 m.entary 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 

 little 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 



