454 Mr. F. W. Jordan on the Direct 



The experimental results obtained show, however, that 

 there is practically no difference in the intensities for the 

 two gases, which proves that the bombardment theory is 

 quite untenable. 



In conclusion my best thanks are due to Professor Barkla 

 for his interest and encouragement during the carrying out 

 of these experiments. 



Wheatstone Laboratory, 

 Kino-'c$ College. 



LIII. The Direct Measurement of the Peltier Effect. 

 Ihj F. W. Jordan, A.R.C.S., B.Sc* 



rilHE Peltier coefficient may be measured directly by the 

 I calorimetric methods of Le Ilouxf and Jahn:f,or it 

 may be deduced from the thermoelectric power by using the 

 thermodynamic relation 



p_rpdE 



a I. 



where P = Peltier coefficient, 



and jTp =the thermoelectric power at the absolute tempe- 

 dl rature T. 



The methods of Le Roux and Jahn are tedious, and can 

 only be applied when one of the junctions is isolated thermally 

 from the other. The apparatus described in this paper was 

 designed in 1909 for the direct measurement of the Peltier 

 coefficient between copper and a short specimen of crystallized 

 bismuth in the limited space between the poles of an electro- 

 magnet. Pellat§, in 1901, suggested a somewhat similar 

 method, but he does not appear to have made an experiment 

 to test its accuracy. He discusses the case of a compound 

 bar of iron and zinc traversed by a current of 20 amperes in 

 such a direction that heat is absorbed at the junction. He 

 suggested that the Peltier absorption of heat might be com- 

 pensated by the heat evolved by a current through a fine 

 insulated wire embedded in the iron close to the junction. 

 The Peltier effect will produce in each bar a temperature 



* Communicated by the Author. 



* Le Roux, Arm. de Chimie et de Phys. i. p. 201 (1&G7). 

 \ H. Jahn, Wied. Ann. xxxiv. p. 755 (1888). 



§ Pellat, Cumptes liendus, cxxxiii. p. 921 (1901). 



