of Tourmaline for Heat. 



429 



rests on the tourmaline plate. Both the junction and the p]ate 

 are allowed to acquire the temperature of the room; the under 

 surface of the slice is then cooled to 0° C. by bringing it in 

 contact with a smooth surface of ice, and the change of tem- 

 perature is read off on the scale of a delicate mirror-galvano- 

 meter. The galvanometer (fig. 1, G) used by me was one of 

 small resistance, with an astatic needle and a powerful damper. 



Fig. 1. 



Jt 



m 



The one junction (a) of the thermoelectric element (a copper 

 cylinder about 4 millim. high, upon the surface of which a 

 platinum and an iron wire were soldered) rested, to insure 

 good contact, upon a small layer of mercury (6) on the tour- 

 maline plate (/); both junctions of the platinum and iron 

 wires with the galvanometer- wires dipped into a glass vessel 

 (c) containing oil of turpentine, which was placed in a wooden 

 box lined with cotton-wool in order to keep the temperature 

 as constant as possible. The temperatures were read off upon 



