i3 The Smithsonian Institution 



science at that day it was impossible that any finite mind 

 should have reached. 



In addition to his brilliant contributions to electrical science, 

 he carried on studies in many other departments of physics. 

 Those in meteorology were very extensive. His experiments 

 upon the effect of the discharge of lightning from the clouds, 

 and upon the condition of lightning-rods while transmitting 

 discharges of electricity, were perhaps the most conspicuous 

 of these. In molecular physics his attention was given to 

 capillary absorption and the cohesion of liquids, as well as 

 to a discussion of the atomic hypothesis of Newton. 



He made investigations on certain phenomena connected 

 with light and heat. By his experiments on the phosphoro- 

 genic ray of the sun, he first demonstrated that it is polariza- 

 ble and refrangible by the laws which govern light. In con- 

 nection with Professor Alexander, he carried on a series of 

 experiments on the relative heat-radiating power of the sun- 

 spots. He reflected heat from concave mirrors of ice, and 

 from his experiments drew conclusions as to the source of the 

 heat derived from the moon. He constructed a thermal-tele- 

 scope, composed of a common pasteboard tube, covered with 

 gilt paper and blackened internally, with which he measured 

 the heat of distant objects : with this he could detect the heat 

 of a man's face a mile off, and that of a house five miles off; 

 and with it ascertained that the coldest spot of the sky is at 

 the zenith. He also invented the method now generally em- 

 ployed for determining by the use of electricity the velocity 

 of the flight of projectiles. 



Not only in ingenious experiment and the interpretation of 

 its results, not only in the practical application of Nature's 

 laws, but still more in his philosophical comprehension of 

 Nature was manifested the greatness of Henry. The English 

 physicist Fleming, in a recent work, writes : 



