DOVE ON THE ELECTRICITY OF INDUCTION. 141 



of forged iron, steel and pig iron in the other spiral, retain their 

 more powerful action when the mass opposed to them is many 

 times their own mass; fourteen insulated wires 0"''70 in diame- 

 ter compensate exactly the cylinder of forged iron. If however 

 the more powerful bundles of wire are enclosed in entire brass 

 tubes, the same solid cylinders then overpower them in their 

 magnetizing action. 



In relation to the magnetizing of steel needles, therefore, the 

 phaenomena are quite analogous, whether the magnetizing is 

 effected by galvanic or by frictional electricity, and that differ- 

 ence which was observed in the physiological effects is no longer 

 here perceptible, i. e. iron in whatever form it is used, or in what- 

 ever manner it may have been magnetized, increases the magne- 

 tizing action upon steel exerted by the current induced in the 

 secondary wire by the connecting wire ; whilst, when the iron is 

 magnetized by the discharge of a battery, it only increases the 

 physiological action of the spiral when it is divided into wires, 

 or is in the form of a longitudinally cut tube ; on the contrary, 

 it effects the same under any form when it is magnetized by the 

 influence of a galvanic current. 



3. Calorific action of the induced current. 



The heating influence of the induced current is independent of 

 its direction. It was therefore measured with a single pair of 

 spirals, which was employed empty, and into which the sub- 

 stances to be tested could be inserted. An elevation of tempe- 

 rature points therefore directly to an increase of power in the 

 current, a diminution thereof to a decrease. An electric air 

 thermometer and a Breguet's metallic thermometer were em- 

 ployed for measuring the temperature. 



54. When magnetism is produced by frictional electricity, 

 the measured calorific effect of the current induced in the secon- 

 dary wire by the connecting wire is weakened both by bundles 

 of iron wire, by iron bars and by nickel ; their action is therefore 

 the same as that of unmagnetic metals, in which the same has been 

 demonstrated by M. Riess. If however the primary magneti- 

 zing current is that of a galvanic battery, masses of iron and 

 bundles of iron wires increase the calorific action of the induced 

 current. 



