RECENT PROGRESS IN PHYSICS. 339 



|ke are able to determine how much heat is produced by the action of 

 24, 53, 82, 101 coils of the main wire. This gives — 



With 24 coils 3.5 



53 '' 6.r 



82 " 11.2 



101 " 14.0 



t Thus the heat produced is very nearly proportional to the number 

 bf acting coils of the main wire ; hence it follows that tJie quan- 

 tity of electricity generated by the conducting circuit of the battery in a 

 Secondary wire is proportional to the length of the acting part of the 

 hircuit wire, other circumstances being equal. 



\ If over the same main spiral A A the same lateral spiral be wound, 

 first with its coils parallel to those of the main spiral, and then with 

 more open coils, so that the main spiral acts always in the direction 

 bf its entire length, but at first upon a long part of the lateral wire 

 running parallel with it, and then on a shorter and more open part ; 

 |in the latter case the action evidently is as much less as the direction 

 bf the coils in the spirals differs, or the closer the lateral spiral is in 

 ^lomparison with the main spiral. 



\ All the coils used for these experiments were wound to the right. 

 {[t is not a matter of indifterence, as far as regards the strength of the 

 Secondary current, whether the lateral spiral is wound in the same or 

 fthe opposite direction to that of the main spiral. Upon a main spiral 

 Wound to the right, eight inches of copper wire were wound first to 

 the right, then to the left, with the result : 



Heat. 



Secondary spiral to the right 15.4 



" " to the left.. 2.7 



§ 60. Action of the mainioire on diff'trent secondary ivires. — A piece, 

 \{a b,) 26 inches long, of the same wire which* formed the main wire 

 -■was stretched out straight ; parallel with it a piece (c d) of the lateral 

 wire was stretched. The whole secondary circuit, in which the elec- 

 trical thermometer was inserted, consisted of copper and iron wire. 

 The piece c d of the secondary circuit, lying opposite a b, being a 

 part of the iron or of the copper wire which forms the lateral circuit, 

 with equal charges of the battery the temperature of the thermometer 

 is the same, provided the iron and copper wire have the same diameter 

 and the space between a b and c d ia the same. 



j Therefore, if the resistance to conduction of the whole secondary 

 ► [circuit remains unchanged, it is perfectly indifferent for the strength 

 !of the secondary current whether a better or worse conducting piece 

 ■of wire is exposed to the action of the main wire. 

 j It is impossible for me to understand clearly the arrangement of the 

 (experiments relating to this matter from the description given. — 

 !(Pog. Ann., L, 3.) 



§ 61. Decrease of the secondary current in proportion to the distance 

 ^from the main loire. — To find how the action on the secondary wire 

 ^decreases with the distance from the main wire, the piece running 

 [parallel must have a great length, because otherwise, at tolerably 



