320 MEMORIAL OF JOSEPH HENRY. 



a resume of the electrical phenomena exhibited by the Leyden jar, 

 an il their true interpretation, he remarked that "for the last three 

 and a half years, all his time and all his thoughts had been given 

 to the details of the business of the Smithsonian Institution. He 

 had been obliged to withdraw- himself entirely from scientific 

 research; but he hoped that now the Institution had got under 

 ua\ . and the Regents had allowed him some able assistants, that In 1 

 would I"' enabled in part at least to return to his first love — the 

 investigation of the phenomena of nature. ' 



Thermal '/'< kscope. — Shortly after his establishment at Washing- 

 ton, he continued a series of former experiments with the "thermo- 

 ealvanie multiplicator" devised by Nobili and Melloni in 1831 ; 

 and by some slight but significant modifications of the apparatus, 

 lie succeeded in imparting to it a most surprising delicacy of action. 

 With the thermo-electric pile carefully adjusted at the focus of a 

 suitable reflector, his '-thermal telescope" when directed to the 

 celestial vault, indicated that the heat radiated inward by our 

 atmosphere when clear, i- least at the /enith, and increases down- 

 ward to the horizon; as was to have been inferred from its increas- 

 ing mass: when directed to clouds, they were found to differ very 

 widely accordingly as they were condensing or ban- dissipated; 

 some even indicating a less amount of radiation than the surround- 

 ing atmosphere. When directed to a horse in a distant field, it- 

 animal heat concentrated on the pile, was distinctly made manifest 

 on the galvanometer needle. Even the heat from a man's face at 

 the distance of a mile could be detected; and that from the side of 

 a house at several miles distance.! These and many similar obser- 

 vations demonstrated to sense the inductions of reason, that there 

 i- a constant and universal exchange by radiation in straight lines 

 from every object in nature, following the same laws as the palpable 

 emanation from incandescent bodies; ami that even when the 

 amplitude of the thermal vibration- (equivalent to the square root 

 of their dynamic energy) is reduced a million fold, its existence 

 may still be distinctly traced. 



!;,„■,,, I. Am Assoc llli Meeting, New Haven, Aug 1850, p !78, 

 tSilliman's Am. Jour. Sei. .Ian IMS vol. V pp 113, lit. 



