Electric Currents by Magnetism and Heat. 65 



screws at the back ; those screws are hut partly shown in the sketch, 

 and are for the purpose of connexion with a suitable galvanometer. 

 The armatures F, F, are grooved on their upper edges, and the iron 

 wire lies in these grooves in contact with them ; and to prevent the 

 electric current passing through the magnet, a small piece of paper 

 or other thin non-conductor is inserted between the magnet and one 

 of the armatures. The battery employed consisted of six Grove's ele- 

 ments (arranged in one series), with the immersed portion of platinum 

 plates about 5 inches by 3 inches ; it was sufficiently strong to heat 

 an iron wire of 1*03 millim. diameter and 20*5 centims. long to a low 

 red heat. 



By making the contacts of the battery in unison with the move- 

 ments of the galvanometer-needles, a swing of about 12 degrees of 

 the needles each way was obtained. The galvanometer was not a very 

 sensitive one; it contained 192 turns of wire. Similar results were 

 obtained with a coil S inches long and 1| inch in diameter contain- 

 ing 16 layers, or about 3/76 turns of wire of 0"415 millim. diame- 

 ter (or No. 26 of ordinary wire-gauge), and a permanent magnet 10 

 inches long. Less effects were obtained with a 6 -inch coil consisting 

 of 40 layers, or about 10,000 turns of wire 0* 10 millim. in diameter, 

 also with several other coils. The maximum effect, of 12 degrees 

 each way, with six Grove's cells in one series was obtained when the 

 wire became visibly red-hot, and this occurred with an iron wire of 1 *03 

 millim. diameter (or No. 19 of ordinary wire-gauge) ; but when em- 

 ploying ten such cells as a double series of five, the maximum effect 

 was then obtained with an iron wire of 1/28 to 1*58 millim. diameter 

 (size Nos. 1/and 18), the deflection being 16 degrees each way. By 

 employing a still thicker wire and a battery of greater heating-power 

 still greater effects were obtained. 



The galvanometer was placed about 8 (and in some instances 1 2) 

 feet distant from the coil. A reversal of the direction of the battery- 

 current did not reverse or perceptibly affect the current induced in 

 the coil ; but by reversing the poles of the magnet, the direction of 

 the induced current was reversed. On disconnecting the battery, 

 and thereby cooling the iron wire, a reversed direction of induced cur- 

 rent was produced. By substituting a wire of pure nickel 24*5 cen- 

 tims. long and 2'lmillims.in diameter, induced currents were obtained 

 as with the iron, but they were more feeble. No induced current 

 occurred by heating the iron wire if the magnet was absent; nor was 

 any induced current obtained if the magnet was present and wires 

 of palladium, platinum, gold, silver, copper, brass, or german-silver 

 were heated to redness instead of iron wire, nor with a rod of bis- 

 muth of 3*63 millims. diameter enclosed in a glass tube and heated 

 nearly to fusion ; it is evident, therefore, that the axial wire must be 

 composed of a magnetic metal. 



No continuous current (or only a very feeble one) was produced in 

 the coil by continuously heating the iron wire. In several experi- 

 ments, by employing twelve similar Grove's elements as a double series 

 of six intensity, an iron wire of 1'56 millim. diameter was made bright 

 red-hot ; and by keeping the current continuous until the galvano- 

 meter-needles settled nearly at zero, and then suddenly disconnecting 



Phil. Mag. S. 4. Vol. 38. No. 252. July 1869. F 



