Detection of Heat by Convection. By L. C. Cooley, Ph. D. 



[Read before the Albany Institute, April 1, 1873.] 



In the course of a series of experiments on certain elec- 

 trical actions, the electroscope in use, which was one of 

 Coulomb's form, gave some anomalous and unexpected 

 results. Its needle would respond with great promptness 

 to the attraction of all the usual electrics, but what was, 

 for a moment, a little puzzling, was the fact that it would 

 swing with equal alacrity whenever such good conductors as 

 iron and copper, after gentle friction, even while held in 

 the hand, were brought into its vicinity. Evidently under 

 such circumstances the motion of the needle could not 

 be due to any electrical action : it was quickly seen to be 

 caused by the gentle rise of temperature in the solid 

 rubbed. So gently warmed by friction the metals became 

 centres of disturbance in the air. The cooler portions 

 around flowed toward the heated centre to take the place 

 of the lighter air pushed upward. The pith ball of the 

 electroscope, caught in these delicate currents, was wafted 

 toward the body introduced. Its motion, therefore, de- 

 clared the presence of the heat. 



Can this principle be applied in the construction of ther- 

 moscopes? As one step toward answering this question, a 

 very slender glass tube, five or six inches long, weighing 

 a few grains only, was suspended by a single fibre of silk, 

 about a foot in length, attached so as to balance it in a 

 horizontal position and hung within a glass case to pro- 

 tect it from air currents. An opening was left in the 

 cover for the introduction of the body to be tested and a 



