EECENT PROGRESS IN PHYSICS. 343 



circuit of a battery (Pog. Ann._, XLIX, 393) a copper wire 13 feet long 

 and 0.55 line thick, which was coiled in a flat spiral on a wooden disk 

 six inches in diameter, covered with pitch and supported by a glass 

 flag, as represented by fig. 61. A series of experiments, made with 

 fthe circuit thus arranged, gave — 



h = 0.43 -^ 

 s • 



( A copper plate 6 inches 10 lines in diameter and 0.33 line thick 

 [was placed parallel to the main spiral, at a distance of 2| lines. It 

 gave — 



* 2 



h = 0.41 ^ 



s ' 



Then a secondary spiral exactly like the main spiral was placed 

 parallel to it, the ends being in perfect metallic contact. This arrange- 

 ment gave — 



h = 0.42 -^ 



s ' 



Hence, neither the copper disk nor the secondary spiral had a sensi- 

 ble influence on the temperature of the conducting circuit. Instead 

 of the perfect metallic closure, a less perfect closure of the secondary 

 spiral was made ; that is, the ends of the copper wire were connected 

 jby a platinum wire 138 lines long and 0.023 in. radius. The secondary 

 ! spiral thus closed being placed 5 lines distant from the main spiral 

 I the result was — 



' h = 0.32-^; 



s 



t 



I when placed at the distance of only 2| lines from the main spiral the 



I result was — 



h = 0.27 A 

 s 



The secondary spiral, closed by a German silver wire 460 lines 

 i long and one-twelfth line diameter, and placed 2^ lines from the main 

 spiral, gave — 



h = 0.17 A 

 s 



The secondary spiral, closed by a glass tube filled with water 9 

 inches long, gave — 



^ = 0.39 A 



s 



We will now subject these results to a somewhat closer examination. 

 The current in the conducting circuit, as seen above, generates a 



