198 Prof. Faraday on Electric Induction — 



dependent nature of induction, conduction, and insulation (Ex- 

 perimental Researches, 1318, &c.). I am deeply indebted to 

 the Company, to the Gutta Percha Works, and to i\Ir. Latimer 

 Clarke, for the facts ; and also for the opportunity both of seeing 

 and showing them well. 



Copper wire is perfectly covered with gutta percha at the 

 Company^s works, the metal and the covering being in every 

 part regular and concentric. The covered wire is usually made 

 into half-mile lengths, the necessary junctions being effected by 

 twisting or binding, and ultimately soldering ; after which the 

 place is covered with fine gutta percha, in such a manner as to 

 make the coating as perfect there as elsewhere : the perfection 

 of the whole operation is finally tried in the following striking 

 manner by Mr. Statham, the manager of the works. The half- 

 mile coils are suspended from the sides of barges floating in a 

 canal, so that the coils are immersed in the water whilst the two 

 ends of each coil rise into the air : as many as 200 coils are thus 

 immersed at once ; and when their ends are connected in series, 

 one great length of ] 00 miles of submerged wire is produced, 

 the two extremities of which can be brought into a room for 

 experiment. An insulated voltaic battery of many pairs of zinc 

 and copper, with dilute sulphuric acid, has one end connected 

 with the earth, and the other, through a galvanometer, with 

 either end of the submerged wire. Passing by the first effect, 

 and continuing the contact, it is evident that the battery current 

 can take advantage of the whole accumulated conduction or 

 defective insulation in the 100 miles of gutta percha on the wire, 

 and that whatever portion of electricity passes through to the 

 water will be shown by the galvanometer. iNow the battery is 

 made one of intensity, in order to raise the character of the proof, 

 and the galvanometer employed is of considerable delicacy ; yet 

 so high is the insulation, that the deflection is not more than 

 5°. As another test of the perfect state of the wire, when the 

 two ends of the battery are connected with the two ends of the 

 wire, there is a powerful current of electricity shown by a_ much 

 coarser instrument ; but when any one junction in the coui'se of 

 the 100 miles is separated, the current is stopped, and the leak 

 or deficiency of insulation rendered as small as before. The 

 perfection and condition of the wire may be judged of by these 

 facts. 



The 100 miles, by means of which I saw the phaenomena, 

 were thus good as to insulation. The copper wire was ^'gth of 

 an inch in diameter ; t^ie covered wire was y^^^^s '> ^^^^ was a 

 little less, being ^^\^^?> in diameter ; the gutta percha on the 

 metal may therefore be considered as 0*1 of k\\ inch in thickness. 

 100 miles of like covered wiie in coils were heaped up on the 



