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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



long SO that all desired positions can be reached without moving the 

 constant temperature bath. Holding the device by the wooden handle, 

 one presses lightly the four prongs of spring wire p upon the surface 

 whose temperature is desired. This places the junction in excellent 

 contact with the surface. There is no backing to the junction save a 

 single silk thread, and thus no possibility of heat piling up and caus- 

 ing too high temperatures. For about |- cm. on each side of the junc- 



FiG. 5. — Calibrating bath. 



/ — Thermoelement device. 

 B — Insulation of cotton batting. 



tion, the wire also touches the surface and assumes the surface tem- 

 perature, thus eliminating error due to cooling of the junction by 

 conduction along the wires. 



Instead of a potentiometer for measuring microvolts, the thermo- 

 element was calibrated by plotting galvanometer deflections directly 

 against temperature differences between the two junctions. A kero- 

 sene bath (fig. 5) was prepared in which the thermoelement device 



