WIRELESS TELEPHONY FESSENDEN. 179 



ance the receiver will obviously not record the higher harmonics. 

 I have experimentally determined that a receiver which restores 

 itself in the ten thousandth part of a second acts with sufficient 

 rapidity. 



HISTORY OF THE DEVELOPMENT OF WIRELESS TELEPHONY. 



The writer has been asked on several occasions how the wireless 

 telephone came to be invented. In November, 1899, shortly prior 

 to the delivery of my previous paper,'^ while experimenting with 

 the receiver shown in figure 3 of that paper, I made some experiments 

 with a Wehnelt interrupter for operating the induction coil used for 

 sending. 



In the receiver mentioned the ring of a short-period Elihu Thom- 

 son oscillating current galvanometer rests on three supports, i. e., 

 two pivots and a carbon block, and a telephone receiver is in circuit 

 with the carbon block. A storage battery being used in the receiver 

 circuit '' it was noticed that when the sending key was kept down 

 at the sending station for a long dash the peculiar wailing sound of 

 the Wehnelt interrupter was reproduced with absolute fidelity in 

 the receiving telephone. It at once suggested itself that by using a 

 source with a frequency above audibility wireless telephony could 

 be accomplished. 



Professor Kintner, who was at that time assisting me in these 

 experiments and to whose aid their success is very largely due, w^as 

 kind enough to make the drawings for an interrupter to give 10,000 

 breaks per second. Mr. Brashear, the celebrated optician, kindly con- 

 sented to make up the apparatus, and it was completed in January 

 or February, 1900. 



The experimental work was, however, delayed, as the writer was 

 at that time transferring his laboratory from Allegheny, Pennsyl- 

 vania, to Rock Point, Maryland, and it was not until six months later 

 that the stations at that point were completed and a suitable mast 

 was ierected for trying the apparatus. 



The first experiments were made in the fall of 1900 w^ith the above- 

 mentioned apparatus, which was supposed to give 10,000 sparks per 

 second, but which probably gave less. Transmission over a distance 

 of 1 mile was attained, but the character of the speech was not good 

 and it was accompanied by an extremely loud and disagreeable noise, 

 due to the irregularity of the spark. 



By the end of 1903 fairly satisfactory speech had been obtained by 

 the arc method above referred to, but it was still accompanied by a 

 disagreeable hissing noise. In 1904 and 1905 both the arc method and 



* Transactions American Institute Electrical Engineers, November 22, 1899. 

 6 United States patent No. 706736, December 15, 1S99. 



