1866.] 



Presidenfs Address. 



281 



Fraunliofer^ Lamont, and otliers have at various times attempted to ob- 

 serve the spectra of the planets and fixed stars ; yet^ though provided with 

 powerful instruments, they obtained no important results. 



Mr. Huggins and Dr. Miller devised a method of seeking in the spectra 

 of the fixed stars that evidence of the existence in them of known elementary 

 substances which had been obtained in the case of the sun by Bunsen and 

 Kirchhoff. A preliminary investigation of the spectra of the more im- 

 portant of the terrestrial chemical elements, and their direct comparison 

 with the lines in the spectrum of common air, was undertaken by Mr. 

 Huggins, with the view of providing a standard scale of comparison, which, 

 unlike the solar spectrum, would be always at hand when stellar observa- 

 tions are possible. This was in itself a work of enormous'labour ; and when 

 completed, the spectra of the fixed stars, including those of some double 

 stars of contrasted colours, were attacked by the two investigators ; and 

 by a happy adaptation of comparatively moderate instrumental means, and 

 unwearied diligence in observiiig and determining by micrometrical mea- 

 suremiCnts the positions of objects that all but elude human vision, their 

 researches have been rewarded by the most complete success. 



The spectra of the stars were compared by a method of simultaneous 

 observation with the spectra of many of the terrestrial elements. It is 

 upon this method of direct comjjarison that the trustvrorthiness of the 

 results obtained chiefly depends, and in tbis respect these observations 

 stand alone. . [In 1815 Fraunhofer recognized several of the solar lines in 

 the spectra of the Moon, Yenus, and five of the fixed stars. In 1862 

 Donati published diagrams of three or four lines in fifteen stars. Re- 

 cently Secchi, Eutherford, and the Astronomer Royal have given dia- 

 grams of the positions, obtained by measurement only, of a few strong 

 lines in several stars.] Eighteen stars have afforded spectra containing 

 lines coinciding with the lines of many of the elementary substances. In 

 thirty-seven more the spectra are full of lines which have not yet been 

 fully compared. 



On extending these researches to the Nebulae, Mr. Huggins made the 

 most unexpected discovery that the spectra of certain of these bodies are 

 discontinuous, consisting of bright lines only, whence he drew the conclu- 

 sion that " in place of an incandescent solid or liquid body transmitting 

 light of all refrangibilities through an atmosphere which intercepts by ab- 

 sorption a certain number of them — such as our sun appears to be — we 

 must probably regard these objects, or at least their photo-surfaces, as 

 enormous masses of luminous gas or vapour. For it is alone from matter 

 in a gaseous state that light consisting of certain definite refrangibilities 

 only, as is the case with the light of these nebulae, is known to be emitted." 



During the last two years jNIr. Huggins has examined the spectra of more 

 than sixty nebulje and clusters. This examination shows that these re- 

 markable bodies may be divided into two great groups : viz. 1st, true or 

 gaseous nebulae, which furnish a discontinuous spectrum, consisting of two 



