"270 Ca.pt. EL B. Jackson. On some Phenomena [May 1, 



To further verify that it was the system of transmission that was 

 the cause of this cessation of signals, a syntonic method, of the same 

 approximate frequency of transmission, though of rather less power, 

 was used alternately with the other system. Signals were exchanged 

 perfectly with the syntonic method, but on reverting to the other 

 method, the signals again ceased. 



This was tried repeatedly with identical results. Many other similar 

 cases have been recorded, but the effects are not always so equally well 

 marked, even under identical circumstances. 



I consider this effect is due to want of synchronism in the oscillatory 

 discharge between the spark balls of the transmitter. This want of 

 synchronism has also been observed by others in the photographs of 

 oscillatory spark discharges. C. Tissot* especially remarks that, in his 

 apparatus (presumably used for a wireless telegraph transmitter), the 

 images of the successive sparks are not equidistant, and that the first 

 interval is always greater than the other intervals, which also decrease 

 very slightly. This implies that the first wave emitted is longer than 

 the second, and so on. Owing to the rapid damping of our form of 

 transmitter, probably only the first two or three waves emitted are of 

 any practical value in exciting the coherer in wireless telegraphy at a 

 distance of 30 miles ; and to excite it at such distances with the power 

 used in these transmitters, it is probably essential that the effects of 

 the successive waves should be cumulative in their action, and for them 

 to be so they must syntonise with the natural period of oscillation of 

 the receiving circuit, which period, in the cases under notice, was the 

 mean frequency of the waves emitted by the transmitter as nearly as 

 this could be practically adjusted. 



Consider the first two waves emitted, or the interval between the 

 first and fifth sparks of the oscillatory discharge, when the third one 

 is not spaced midway between them ; the resulting waves, differing but 

 little in length, and moving with equal velocities and in the same 

 direction, leave a point " " (the spark gap), the second starting a mean 

 wave-length behind the first one, and in the same phase ; at some fixed 

 point, " P," in their path, owing to the difference in their length, the 

 two waves will pass that point in the opposite phase, and at a point, 

 " Q," approximately double the distance from " " that "P" is from 

 " 0," they will pass " Q," again in the same phase, and so on, as at all 

 points the second wave is a mean wave-length behind the first one. 

 To excite the coherer, under the conditions presumed to be necessary for 

 long distances, the impulses due to these waves must syntonise with 

 the natural period of oscillation of the receiving circuit, and therefore 

 these successive waves must pass by that circuit (wherever it may be), 

 with the second following in the same phase as the first, or nearly so, 



* ' Comptes Kendus,' vol. 132, p. 763 (25/3/01) ; and vol. 133, p. 929 (2/12/01). 



