THE 



POPULAR SCIENCE 

 MONTHLY. 



MAY, 1878. 



THE RADIOMETER: A FRESH EVIDENCE OF A 

 MOLECULAR UNIVERSE. 1 



By JOSIAH P. COOKE, Jr., 



ERVING PROFESSOR OF CHEMISTRY AND MINERALOGY IN HARVARD UNIVERSITY. 



~~VT~0 one who is not familiar with the history of physical science can 

 -L i appreciate how very modern are those grand conceptions which 

 add so much to the loftiness of scientific studies ; and of the many who, 

 on one of our starlit nights, look up into the depths of space, and are 

 awed by the thoughts of that immensity which come crowding upon 

 the mind, there are few, I imagine, who realize the fact that almost all 

 the knowledge, which gives such great sublimity to that sight, is the 

 result of comparatively recent scientific investigation ; and that the 

 most elementary student can now gain conceptions of the immensity of 

 the universe of which the fathers of astronomy never dreamed. And 

 how very grand are the familiar astronomical facts which the sight of 

 the starry heavens suggests ! 



Those brilliant points are all suns like the one which forms the cen- 

 tre of our system, and around which our earth revolves ; yet so incon- 

 ceivably remote, that although moving through space with an incredible 

 velocity they have not materially changed their relative position since 

 recorded observations began. Compared with their distance, the dis- 

 tance of our own sun 92,000,000 miles seems as nothing; yet how 

 inconceivable even that distance is when we endeavor to mete it out 

 with onr terrestrial standards ! For, if, when Copernicus the great 

 father of modern astronomy died, in 1543, just at the close of the 

 Protestant Reformation, a messenger had started for the sun, and trav- 

 eled ever since with the velocity of a railroad-train thirty miles an 

 hour he would not yet have reached his destination ! 



1 A lecture delivered in the Sanders Theatre of Harvard University, March 6, 1878. 



VOL. XIII. 1 



