OF ARTS AND SCIENCES. 



39 



For this purpose I naturally had recourse to a thermo-electric 

 device.* 



The engine belonging to the Harvard Physical Laboratory, with 

 which my experiments were made, is a Kendall and lioberts of 

 10-inch cylinder and lo-inch stroke, provided with an ordinary 

 Myer's valve and cut-off. It is jacketed by an air space about 

 2 cm. wide. 



/t 



\ 



\=SA 



f^^ 



i 



J^/.y. 1. 



Figure 1 shows a horizontal longitudinal section of the cylinder, 

 with the piston at the beginning of its forward stroke. The cylin- 

 der wall, about 2 cm. in thickness, is pierced at o for making 

 connection with an indicator. Into this hole, which is about 

 2 cm. wide, I screwed a plug represented accurately enough by 

 Figure 2. On the inner end of this plug was soldered a cover of 



FUf.2. 



thin steel, 8. Through two holes in the plug, and insulated from 

 it by glass tubes, two rods extended to touch the steel cover, one, 

 A, of antimony, the other, 5, of bismuth. To the outer end of A, 

 at a, was soldered a copper wire ; to the outer end of B, at h, was 

 soldered a similar wire. These two wires lead to a ballistic gal- 

 vanometer, but at one point the electric circuit was broken, except 



* A letter received from Mr. Bryan Donkin, Jr., of Lotnlon, the well known 

 engine builder, after the first account of my experiments was published, showed 

 me that he had been before me in making experiments in tiie same general man- 

 ner, but witli small bulb thermometers in mercury cisterns instead of thermo- 

 piles. The Bulletin de Society de Mxdhouse for 1890 contains some account of 

 his work. My results appear to be not discordant with those which he obtained. 



