MECHANICS AND USEFUL ARTS. 107 



out of the old Atlantic cables, and who is again in charge of the 

 electrical arrangements on board of the Great Eastern. In the 

 old form of testing, the official at" the shore-end had to insuhite 

 the cable, when any test was taken, and consequently was un- 

 aware of what was going on. In the present plan a constant test 

 can be kept up, with the knowledge of both ship and shore. The 

 cable is attached at the shore-end having high-resistance through 

 a galvanometer to earth ; this resistance is so high that, on the 

 sliip keeping up a current from a large battery, the resistance is 

 so great that a readable deflection can be obtained. A galva- 

 nometer is also inserted in the circuit on l)oard ship. If the cur- 

 rent were maintained, the deflection on the two galvanometers 

 "svould remain constant, and during the paying out the deflections 

 would be constantly watched ; if they remained constant, the cable 

 remained in the same electrical condition, but if they altered, they 

 would show at once, both ship and shore, that something was 

 wrong: to ship that by the increased deflection through a fault 

 there was less resistance, and consequently more current flowing 

 in to cause the increased deflection. On the shore the efi'ect 

 would be difi'erent, as, there being another method to escape, less 

 current would arrive. By this means we see how the appearance 

 of a fault would be easily detected. The system of speaking or 

 exchanging signals is very simple : by means of a condenser at- 

 tached to the cable, which is charged Avith the same potential or 

 opposite potential as the cable, the deflection is slightly altered 

 in one direction or the other, and communication can be ex- 

 changed without interfering with the constant test. 



THE BLACK SEA CABLE. 



It is announced that the cable of the Indo-European Telegraph 

 Co. across the Black Sea, about 200 miles, has been successfully 

 submerged. — Engineering^ July 16, 1869. 



THE INDO-EUROPEAN TELEGRAPH. 



The lines from London to Norderney, which constitutes part of 

 the system, are in working order, and from Norderney to Thorn, 

 on the Prusso-Russian frontiers, two wires are being constructed 

 by the Prussian government. 



From Thorn to Balta, via Warsaw, the section will consist of 

 800 miles of line, which will be laid on posts of heavy timber, 

 principally of oak. From Balta the system will be continued via 

 Odessa to Kertch, on througli the Crimea to Ecaterneador, and 

 thence to a point which will correspond with the northern end of 

 the Black Sea cable. This section, which will, as far as regards 

 the land part, be constructed of iron posts, will be about 750 

 miles in length, and will comprise two cables, — one 15 miles 

 long, which will be sul)merged in tlie Straits of Kertch, and an- 

 other, 4 miles long, which will cross the River Dnieper. The con- 



