RADIATION. 207 



which rendered a body competent to intercept the waves 

 of ether, rendering it competent in the same degree to gen- 

 erate them. Perfumes were next subjected to examination, 

 and notwithstanding their extraordinary tenuity, they were 

 found vastly superior, in point of absorptive power, to the 

 body of the air in which they were diffused. We were led 

 thus slowly up to the examination of the most widely 

 diffused and most important of all vapors — the aqueous 

 vapor of our atmosphere — and we found in it a potent 

 absorber of the purely calorific rays. The power of this 

 substance to influence climate, and its general influence 

 on the temperature of the earth, were then briefly dwelt 

 upon. A cobweb spread above a blossom is sufficient to 

 protect it from nightly chill ; and thus the aqueous vapor 

 of our air, attenuated as it is, checks the drain of terrestrial 

 heat, and saves the surface of our planet from the refriger- 

 ation which would assuredly accrue, were no such sub- 

 stance interposed between it and the voids of space. We 

 considered the influence of vibrating period and molecular 

 form on absorption and radiation, and finally deduced, from 

 its action upon radiant heat, the exact amount of carbonic 

 acid expired by the human lungs. 



Thus in brief outline were placed before you some of 

 the results of recent inquiries in the domain of Radiation, 

 and my aim throughout has been to raise in your minds 

 distinct physical images of the various processes involved 

 in our researches. It is thought by some that natural 

 science has a deadening influence on the imagination, and 

 a doubt might fairly be raised as to the value of any study 

 which would necessarily have this effect. But the experi- 

 ence of the last hour must, I think, have convinced you 

 that the study of natural science goes hand in hand with 

 the culture of the imagination. Throughout the greater 

 part of this discourse we have been sustained by this 

 faculty. We have been picturing atoms, and molecules, 



