THE NEW PROFESSION. 255 



sophic mind perceived that in the fact he named, which to so many of 

 us might seem little more than a curious experiment, lay the principle 

 which, if rightly developed, would make practicable the transmission 

 of power. 



If, now, we could call back this great electrical engineer, and ask 

 him what recent discovery came next in importance to this, what would 

 he reply ? His answer would be the discovery that " a voltaic battery 

 is reversible." The Gramme machine has given us means of trans- 

 mitting power of electricity. The later discovery enables us to store 

 up electrical energy as distinguished from electricity. 



Electrical engineering, which embraces a knowledge of cables, teleg- 

 raphy, electric lighting, electrical measurement, transmission of power, 

 storage-batteries, and how to localize faults in cables, land lines, and 

 telephone lines, has thus become a subject of the first practical im- 

 portance. 



A prominent department of the electrical engineer's work is the 

 localizing of faults in ocean-cables, which may be of five different 

 kinds: 1. Where the copper conductor makes a "perfect earth." 2. 

 Where the copper conductor is broken, and yet the insulation remains 

 unbroken. 3. Where an " imperfect earth " is made. 4. Faults aris- 

 ing from a hole in the gutta-percha sheath, making a connection be- 

 tween the conductor and the sea. 5. From the establishment of a 

 connection between the iron sheathing and the copper core, by a nail 

 or wire driven in. 



The first kind of fault is easily located, because we know the re- 

 sistance of the cable when it is in perfect working order. If, for 

 instance, it has 10,000 ohms, Or units of resistance, a fault making a 

 perfect earth midway in the cable would give us 5,000 ohms resist- 

 ance. Or, we know how many ohms of resistance there are to a mile 

 of cable when it is in perfect working order, and, by the use of deli- 

 cate instruments and by mathematical calculations, we can easily lo- 

 cate the fault. 



The location of the second class of faults, i. e., a complete break- 

 age of the conductor, naturally followed by a total cessation of all 

 communications between the two ends of the cable, may be detected 

 in several ways. The charge which the cable will contain is first 

 measured ; and, when the charge per mile is known, the amount actu- 

 ally observed will directly give the location of the faults; and the exact- 

 ness with which the position of the break can be determined is limited 

 only by the accuracy with which the relative charges can be compared. 

 Suppose, for instance, the discharge from a mile of the cable with 

 a given battery, and reflecting galvanometer, is represented by a de- 

 flection of ten divisions, and the discharge from a cable containing a 

 broken copper conductor is one hundred divisions, we know the fault 

 is about ten miles from the shore. 



A fault of the fourth kind is located very readily. There is a 



