SCIENCE AND PRACTICE. 



371 



Mi*. Whitehouse first sought to refine this crude process 

 by measuring only the current which actually went through 

 the joint, and expressing it in terms of the insulation resist- 

 ance of lengths by the cable. The joint between the lengths 

 a and /3 (Fig. 171) was immersed in acidulated water con- 

 tained in an insulated vessel, v ; a plate of metal, also im- 

 mersed in the water, was connected 

 to one pole of a powerful, well-in- 

 sulated battery, B, the other pole 

 being in connection with one end of 

 a galvanometer coil; the other end 

 of the galvanometer coil, and both 

 ends of the conductor of the cable, 

 were to earth. Whatever current 

 was indicated by the deflection of 

 the galvanometer needle must neces- 

 sarily pass through the water in the 

 insulated vessel, and through the 

 joint. 



This method was employed for 

 some time, but has been succeeded 

 by a modification of it, introduced 

 by Messrs. Bright and Clark, which 

 consists in accumulating the elec^ 

 tricity which goes through the joint upon the plates of a 

 condenser, and sending the discharge suddenly through the 

 galvanometer, instead of letting the current go gradually 

 through, as Whitehouse did. 



This modification is decidedly superior to its original. The 

 two parts, A and B (Fig. 172), of the cable are placed con- 

 veniently, that the joint between them may be immersed in 

 water contained in the insulated vessel, v, from which a con- 

 nection, I, leads to the plate, 2, of the condenser, c. The 

 other side of the condenser is connected with the lever, 1, of 

 a switch, s, the two anvils, 2, 3, of which are respectively in 

 the circuits of a battery, E, and of a galvanometer, G. The 

 other end of the galvanometer coil is connected to side 2 of 

 the condenser, and the other pole of the battery with tho 



BB 2 



