464 Tie Direct "Measurement of the Peltier Effect. 



When the temperature-difference was reversed. 



.— =56*3 X 10" 6 volt per degree, 

 i cit 



with faulty junction at the lower temperature. 



The fault of the junction arose from the temperature 

 gradient along the wires (O'l mm. diam.). This could be 

 remedied by soldering a junction of thinner wires in a groove 

 and winding the insulated leads around the cylinder, in order 

 to minimize the temperature gradient. A junction Mas 

 attached in this way to a similar copper cylinder. The 

 defective junction and the insulated junction were also 

 imitated approximately. The latter was laid in a groove and 

 separated from the cylinder by a thin strip of mica 002 mm. 

 thick. The rest of the groove was packed with cotton-wool 

 and overwound with silk thread. The cylinder was heated 

 electrically inside a copper enclosure, and the following 

 results were obtained : — 



Excess temperature of cylinder over enclosure = 8° nearly. 

 Temperature difference between the perfect"! — qq.o* n 

 and defective junctions J ~~ 



The temperature difference between the perfect and insu- 

 lated junction varied from C, 3 to 0°*45, according to the 

 tightness of the filling of cotton-wool in the groove. 



The results indicate the precautions that must be taken in 

 fixing the thermo-junctions to the cylinder for this particular 

 measurement. It is to be noted that this slight defect in the 

 junctions /', g will not disturb the temperatures in the third 

 column of the table by more than o, l. The high results for 

 the direct measurement of the thermoelectric power are just 

 what are to be expected when the junctions are faulty and the 

 rod is a short one. 



It is intended to conduct experiments with this apparatus 

 in a magnetic field to determine how the Peltier coefficient 

 depends on the strength and direction of the field across the 

 surface of contact of the bismuth with the copper. 



South- We stern Polytechnic, Chelsea, S.W. 

 September 18, 1910. 



