326 BULLETIN OF THE 



focus of a suitable reaector, his " thermal telescope" when directed 

 to the celestial vault, indicated that the heat radiated inward by 

 our atmosphere when clear, is least at the zenith, and increases 

 downward to the horizon ; as was to have been inferred from its 

 increasing mass : when directed to clouds, they were found to 

 differ very widely accordingly as they were condensing or being 

 dissipated ; some even indicating a less amount of radiation than 

 the surrounding atmosphere. When directed to a horse in a dis- 

 tant field, its 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 observations demonstrated to sense the induc- 

 tions of reason, that there is a constant and universal exchange 

 by radiation in straight lines from every object in nature, follow- 

 ing the same laws as the [)alpable emanation from incandescent 

 bodies ; and that even when the amplitude of the thermal vibra- 

 tions (equivalent to the square root of their dynamic energy) is 

 reduced a million fold, its existence may still be distinctly traced. 



Henry showed by experiment, that ice could be employed both 

 as a convex lens for converging heat to a focus, and also as a 

 concave mirror for the same purpose : a considerable portion of 

 the incident rays being transmitted, a large portion reflected, and 

 the remainder absorbed by the ice. 



He presented to the American Philosophical Society, a discus- 

 sion of the problem of the suspension of the ball in a water jet or 

 fountain. f 



In 1849, for the purpose of estimating the effects of certain 

 meteorological conditions of the atmosphere, he made some ex- 

 periments on the lateral radiation from a current of ascending 

 heated air at different distances above the flame ; the latter being 

 thoroughly eclipsed. 



He also experimented on the radiation of heat from a hydro- 

 gen flame, which was shown to be quite small, notwithstanding 

 the high temperature of the flame. By placing an infusible and 

 inconiljustible solid in the flame, while the temperature is much 

 reduced, the radiant light and heat are greatly increased J Re- 

 sults closely analogous to those he obtained in the differences 

 between the audibility of vibrating tuning-forks when suspended 

 by a soft thread, or when rigidly attached to a sounding-board. 

 These results have also an undoubted significance with regard 

 to celestial radiations ; not only as to the differences between 

 gaseous nebulte and stars or clusters, but as to the differences 



* Sill Am. Jour. Sci. .Tan. 1848, vol. v. pp. 113. 114. 

 t Proceed. Am. Phil. Soc. Oct. 16, 1848, vol. iv. p. 285. 

 X Proceed. Am. Phil. Soc. Oct. 19, 1849, vol. v. p. 108. 



100 



