HIGH VOLTAGE — COMPTON 251 



nature of electrical instruments or electrical control devices, and it 

 still remains true that the production and distribution of electricity 

 are basically carried on by means of the electromagnetic induction 

 devices developed from the work of Faraday and Henry. 



Let us follow the development of high voltage by electromagnetic 

 induction. In this, as in all other fields, the first developments were 

 crude, as was necessarily the case because instruments and methods 

 had not been developed and everything had to be taken up de novo. 

 When Joseph Henr}^ wished to build his great magnet with several 

 coils of wire he had first to invent insulated wire, which he did by 

 wrapping strips of his wife's dresses and petticoats covered with 

 shellac around the wire. When Henry wished to measure the voltage 

 of the current produced in a step-up transformer he had no ammeter 

 or voltmeter capable of detecting the small current at high voltage 

 and had to substitute for them the students in his class, judging the 

 voltage by the number of students who could be shocked when con- 

 nected hand to hand in series across the terminals of the secondary 

 of his transformer. Thus a voltage that would shock 30 students he 

 estimated to be twice as high as one which would shock 15 students, 

 and in this way he was able to arrive at a very crude but correct idea 

 of the relationship between the number of turns of wire in the sec- 

 ondary of a transformer and the voltage which was produced therein. 



The story is told of a striking lecture demonstration given by 

 Henry while at Princeton. He hung a secondary coil of a large num- 

 ber of turns of wire on the inside wall of his classroom and had the 

 students of his class join hands in series across the terminal of the 

 coil. The primary coil of this transformer was concealed from the 

 students, being suspended on the outer wall of the building from 

 wires passing out through an attic window and comiected with a 

 large voltaic battery in the attic. When Henry rapped against the 

 wall his assistant in the attic plunged the copper and zinc battery 

 plates into the acid, thus sending a current through the primary, 

 which induced a high voltage in the secondary and shocked the 

 students of his class. 



It is probable that Henry, burdened as he was with administrative 

 duties and the difficulties of finding the means wherewith to carry on 

 his experiments, did not realize so clearly as did his contemporary, 

 Faraday, the ultimate practical value of these things which he was 

 doing. Faraday, when once asked by the King, " What is the use of 

 these things?" replied, "Your jMajesty, of what use is a baby?" 

 And another time, when he was asked by the Prime Minister this 

 same question, " Of what use are these things which you are doing? " 

 he replied, " Your Excellency, some day you may be able to tax these 

 things." Henry, however, was so wrapped up in his scientific pur- 



