140 ANNUAL OF SCIENTIFIC DISCOVERY. 



ON TRANSMISSION OF ELECTRICITY. 



Prof. Farraday has recently completed some experiments on the first 

 effects of a current admitted into an insulated conductor, and to ascertain 

 the causes of the excessive differences which exist between the several ascer- 

 tained velocities of electricity. It is a fact, that in Mr. Wheatstone's ap- 

 paratus it travels at the rate of 100,000 leagues a second, while in the wire 

 connecting London and Brussels, Mr. Airy found it required more than 

 that time to traverse a thousand leagues. As the company for the manu- 

 facture of submarine telegraph wires placed their wires at Mr. Farraday's 

 disposal, he had an excellent opportunity to pursue his researches. The 

 mode adopted by Mr. Statham, (the superintendent of the company,) to 

 ascertain the degree of insulation the gutta percha coated wires possess, is 

 to lay them along large floating frames, in such a way that they shall be 

 completely submerged, with the exception of their two ends, which are 

 kept in the air ; two hundred of these wires are submerged together ; their 

 total length is forty leagues, when they are connected together by their ex- 

 tremities, (which is very easily done.) A battery of 30 pair, connected with 

 the earth by one of its poles, while the other communicates by means of 

 a galvanometer with the submerged wire, is the test employed ; if 

 the gutta percha coating is not perfect, there is a loss of electricity, 

 which is indicated by the galvanometer. I may premise, the submerged 

 wires may be taken out of the water and suspended in the air at the will 

 of the experimenter. Mr. Farraday found the wires, when submerged, 

 acted precisely as though they were a Leyden jar, the wire playing the 

 part of the tin foil coating, the gutta percha the part of the glass, and the 

 water the part of the exterior tin foil coating ; as one electricity was en- 

 gaged in the submerged wire, its major part was dissimulated by the con- 

 trary electricity, which, flowing from the earth, fixed itself in the water in 

 contact with the gutta percha coating, where it accumulated until the ten- 

 sion became so great that the apparatus refused to receive further charges, 

 notwithstanding the play of reciprocal influences. In this state of things 

 all communication established between the wire and the earth reunites the 

 two coatings as an exciter ; but as some time was required to charge the 

 wires, the discharge likewise requires a corresponding time. In the air, of 

 course, (for the water is wanting,) the wire becomes incapable of taking 

 sensible charges. These negative and positive results furnish a striking 

 proof of the identity of static electricity, furnished by the machine, and 

 dynamic electricity, furnished by the battery. This delay the constitution 

 of the submarine telegraph superinduces in the propagation of a current 

 allowed Mr. Farraday to easily make a very beautiful experiment : he sent 

 electrical waves in the wires ; he even sent several, one after the other ; and 

 they did not confound themselves together. But these waves have a ten- 

 dency to diffuse themselves as they advance; for if, after having established 

 the contact between the battery and the end of the wire, the experi- 



