266 Mr. Gore on the Development of Electric Currents [Jan. 28, 



which is also surmounted by a small mercury cup, and is connected with 

 the cylindrical binding-screw I by a copper wire with a middle flattened 

 portion O to impart to it flexibility. The two ends of the fine wire coil 

 are soldered to two small binding-screws at the back ; those screws are but 

 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 /*~s 

 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 

 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 movements o£ 

 the galvanometer-needles, a swing of about 12 degrees of the needles eachj 1 

 way was obtained. The galvanometer was not a very sensitive one ; it coni- 

 tained 192 turns of wire. Similar results were obtained with a coil 

 inches long and lj inch diameter containing 16 layers, or about 3776 

 turns of wire of 0"415 millim. diameter (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. 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 1*03 millim. 

 diameter (or No. 19 of ordinary wire-gauge) ; but when employing ten such 

 cells as a double series of five, the maximum effect was then obtained with 

 an iron wire (size Nos. 17 and 18) 1*28 to 1*58 millim. diameter, the deflec- 

 tion 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 12) 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 current was produced. By substituting 

 a wire of pure nickel 24*5 centims. long and 2 - l millims. 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 bismuth 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 



