332 BELL SYSTEM TECHNICAL JOURNAL 



In his work in 1838 he demonstrated that through the proportioning of 

 the windings of two coils in inductive relationship, the voltage in the 

 secondary circuit could be stepped up or stepped down and here we 

 find the genesis of the modern transformer. The transformer, a device 

 without moving parts, is fundamental to every alternating current 

 system, and it is the principal reason why alternating currents are so 

 generally employed today. Through its use, it is possible to design 

 dynamos for operation at the most effective generator voltage and 

 then step up the voltage by means of a transformer to the most efficient 

 level for use on the transmission lines and then at the distant end of 

 these lines by means of other transformers step down the potential 

 to the most efficient and convenient voltage for use on distributing 

 systems. 



So fundamental was Henry's work that in it we find contributions 

 even to the youngest child of the electrical family, the radio communi- 

 cation art. Not only does it use his general contributions to the art 

 because of the fact that radio communication is simply a specialized 

 form of telephony or telegraphy employing a particular method of 

 transmission, but Henry's work in detecting the discharges of Leyden 

 jars at a distance of 30 feet and later at distances of several hundred 

 feet certainly foreshadows radio transmission. In 1842 Henry wrote 

 as follows in regard to his experiment in which he observed the induc- 

 tive effects of a discharge of Leyden jars at a distance of 30 feet : " . . . 

 when it is considered that the magnetism of the needle [his receiving 

 device] is the result of the difference of two actions, it may be further 

 inferred that the diffusion of motion in this case is almost comparable 

 with that of a spark from a flint and, steel in the case of light." ^ 

 In the notes made early in 1844 by a student recording Henry's 

 lectures on natural philosophy the following occurs: "Hence the 

 conclusion that every spark of electricity in motion exerts these 

 inductive effects at distances indefinitely great (effects apparent at 

 distances of one-half a mile or more) ; and another ground for the sup- 

 position that electricity pervades all space. Each spark sent off from 

 the Electrical Machine in the College Hall sensibly affects the sur- 

 rounding electricity through the whole village. A fact no more 

 improbable than that light from a candle (probably merely another 

 kind of wave or vibration of the same medium), should produce a 

 sensible effect on the eye at the same distance." ^ 



It is certainly a far cry from Henry's observations of inductive effects 



at distances of a few hundred feet to the present use of radio for broad- 



^ "Scientific Writings of Joseph Henry," 1886, Vol. 1, p. 203. 

 * Notes of Wm. J. Gibson, entitled "Lectures on Natural Philosophy by Professor 

 Henry," Feb. 28, 1844, p. 135. 



