.SVA' WILLIAM SIEMENS, F.K.S, 93 



proved, ut great cost, that they were absolutely necessary. There 

 an- other important advantages obtained through the adoption 

 <>f the water tanks : without them the electrical tests during the 

 ] laying out are, to a great extent, illusory, partly on account of 

 disturbances produced by irregular variations of temperature, and 

 partly on account of the impossibility of detecting any fault in the 

 insulating covering, unless the conductor and outer covering are 

 brought into wet contact. If, therefore, faults of insulation occur 

 on board ship, either through partial exposure of the cable to heat, 

 or through an imperfect joint, or through accidental causes, they 

 only make their appearance at the moment when the defective piece 

 enters the sea, or sometimes even days after submersion has taken 

 place. The sudden appearance of such faults has been hitherto of 

 frequent occurrence, giving rise to interruption of the operation of 

 paying out, and entailing great risk by kinks, or bad joints, or of 

 losing the cable entirely when in deep water. In paying out the 

 cable from a wet tank into the sea, these causes of failure are 

 avoided, and the operation is rendered comparatively safe and 

 easy. 



In conducting the electrical tests of the Malta and Alexandria 

 cable in the course of its manufacture, the author made it his chief 

 object to obtain throughout strictly comparative results. For this 

 purpose, it was necessary to adopt a standard measure of resistance, 

 by which to express both the conductivity of the copper conductor, 

 and of the insulating covering. This standard measure has been 

 supplied by the author's brother and partner Dr. Werner Siemens. 

 The unit of resistance according to this system is that of a column 

 of pure mercury (contained in a glass tube), one metre in length 

 between the contact cups, and of one square millimetre sectional 

 area, taken at the temperature of melting ice. Of this unit, which 

 can be readily reproduced with great accuracy, multiples are pro- 

 duced in the form of coils of German silver wire, covered with silk. 

 A number of such coils, representing different values of resistance 

 from 1 to 10,000, are fastened separately to a board of ebonite, the 

 ends being soldered to contact pieces, by which means any number 

 of the coils can be joined, so as to form one electric circuit of 

 known total resistance, expressible in units. The testing apparatus 

 is formed of three such scales of variable resistance, a battery, and 

 a delicate sine galvanometer, or instead, where the space admits 



