RECENT PROGRESS IN PHYSICS. 



345 



It is seen from tliis table how very rapidly at first the temperature 

 )f the circuit of the main spiral decreases with increasing length of 

 jjrerman silver wire inserted in the circuit of the secondary spiral, and 

 >hat a minimum is reached when the 1 ngth of the introduced wire is 

 a9.6 Paris feet, in which case tlie heatiog eiFect is only 48 per cent, of 

 phat wliich is observed with perfect closure of the secondary spiral. 

 jVVhen the length of the wire exceeds 29.6 feet the temperature grad- 

 ually increases again ; and by lengthening the wire to 582 feet the 

 temperature rises to 87 per cent, of that originally obtained. 



A metallic closed circuit near the conducting loire of an electrical 

 \attery acts retardingly on the discharge of the battery in proportion to 

 he length of its closing loire. The circuit of the secondary loire being 

 \)rogreisively prolonged its action successively increases, attains a maxi- 

 num, and then decreases. 



The changes which the temperature in the main wire undergoes by 

 engthening the secondary wire, obey the law indicated by the last 

 'able, whether the charge of the battery be stronger or weaker ; with 

 iitronger charges, as well as with weaker, the "retarding effect of the 

 Secondary wire attains a maximum when the secondary spiral is closed 

 py 29.6 feet of the above-mentioned German silver wire ; and then the 

 [.emperature in the main wire is 48 per cent, of that which would 

 [lave been observed with an equal charge if the secondary spiral had 

 fi perfect metallic closure ; but as soon as the conducting circuit of 

 Ihe main wire is lengthened by the introduction of a thin wire the 

 jourse of the retarding effect of the lateral wire changes. 

 ' In the main conductor a platinum wire 7 inches 5 lines long and 

 ).023 line radius was introduced, and the results in the following 

 :able were obtained ; the lateral spiral being closed by German silver 

 yire of different lengths : 



