PRESIDENTIAL ADDRESS, B.A. 1871. 179 



brightness. In this condition the fluid can be no 

 longer regarded as a gas, and we must judge of its 

 relation to the vaporous or liquid states according 

 to the critical conditions discovered by Andrews. 



While these great investigations of properties of 

 matter were going on, naturalists were not idle 

 with the newly recognised power of the spectro- 

 scope at their service. Chemists soon followed 

 the example of Bunsen in discovering new metals 

 in terrestrial matter by the old blow-pipe and 

 prism test of Fox Talbot and Herschel. Biologists 

 applied spectrum analysis to animal and vegetable 

 chemistry, and to sanitary investigations. But it 

 is in astronomy that spectroscopic research has 

 been carried on with the greatest activity, and been 

 most richly rewarded with results. The chemist 

 and the astronomer have joined their forces. An 

 astronomical observatory has now, appended to it, 

 a stock of reagents such as hitherto was only to be 

 found in the chemical laboratory. A devoted 

 corps of volunteers of all nations, whose motto 

 might well be ubique, have directed their artillery 

 to every region of the universe. The sun, the 



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