Effects in Tellurium. 59 



which is at 25° C. and the other at T°, has been found bj Dr. 

 H. C. Richards to be 



E = 15-20 (T - 25) + 0-0272 (T - 25) 2 . 



One of the couples used in this work was tested between 0° 

 and 100° and found to agree with the formula, which has been 

 used in determining temperatures. 



The plate was insulated and protected from air-currents as 

 well as possible by the use of mica, asbestos, cotton, etc. 



Ettingshausen effect. — If the primary current flow from 

 right to left, and the lines of magnetic force are directed away 

 from the observer, the upper edge of the plate is cooled and 

 the lower warmed. This is in the same direction as in bis- 

 muth. The effect was measured by passing current through 

 the plate between the two tubes, and observing the tempera- 

 tures at the edges of the plate for both directions of the held, 

 giving time in each case for temperatures to become constant. 

 A series of readings was taken, reversing held each time, in 

 order to eliminate any error due to the gradual change in tem- 

 perature of the whole plate. Readings in zero field were not 

 used in the calculations. They showed, however, that the 

 effect was not symmetrical, i. e., the change for one direction 

 of the field was not the same as for the opposite direction of 

 the field ; starting with zero field in both cases. The coeffi- 

 cient of the Ettingshausen effect, P, is defined by the equation 



T = PH- 



t 



where T is the difference in temperature produced, by a 

 change of field H, between the edges of a plate of thickness 

 t when traversed by a current C. Temperatures are measured 

 in Centigrade degrees; other quantities in C.G.S. electro- 

 magnetic units. The values of P observed ranged between 

 0-00014 and 0-00029 for fields up to 5500 gausses, at a tempera- 

 ture of about 65°. The high resistance of tellurium causes a 

 correspondingly large generation of heat and the temperature 

 of the interior is considerably higher than that of the sur- 

 roundings. The flow of heat from the center of the plate to 

 the edges (cooled by water flowing through the tubes) will 

 produce a Leduc effect which may interfere with the measure- 

 ments of the Ettingshausen effect. In this case the measure- 

 ments were made at the center of the plate, where the tem- 

 perature-gradient may be assumed zero. 



Hall effect. — If the primary current flow from right to left, 

 and the lines of force are directed away from the observer, the 

 upper edge is at the lower potential. This direction coincides 

 with the results of other observers and is usually considered as 



