1902.] affecting the Transmission of Electric Waves. 271 



otherwise the tendency of the second one will be to weaken or annul 

 the effect of the first one. 



At the point " P," therefore, when the waves are in opposite phase, 

 it may be expected that signals will be weak, and at " Q," when they 

 are in phase, they may be strong, but, owing to " Q's " distance from 

 " " being double that of " P," the effect of each individual impulse 

 at " Q " is only half its effect at " P," and " Q " may be the maximum 

 distance from " 0," at which the cumulative effect of the successive 

 waves will excite the coherer, even when they are in phase and in per- 

 fect syntony with the receiver circuit. 



I have not yet been able to investigate the exact cause of the non- 

 synchronous emission of the waves, but I attribute these " zones of 

 weak signals " (as I term them) to this non-synchronous emission of 

 the waves, and to the rapid damping of this form of transmitter, and 

 would observe that when using my syntonic transmitter, in which the 

 damping is less rapid, I have never noticed these effects. 



A point of interest, which has also great effect on the signalling 

 distance, is the efficiency of the earth connection of both the trans- 

 mitting and receiving instruments. Fortunately for the system, on 

 board a modern ship there is no difficulty in obtaining an almost 

 perfect earth connection when the ship is at sea. In dry dock, how 

 ever, there is, in fine weather, a great difficulty in doing so, and the 

 effects of the bad earth with the ship in dock, on the signals, are 

 extremely marked, both for transmitting and receiving, reducing the 

 distance as low as to 25 per cent, of the distance with the ship afloat. 



A similar effect due to drought has been observed with some shore 

 stations, where, according to my experiences, the maximum signalling- 

 distances have always been obtained during wet seasons of the year. 



A typical example is given : — 



On one particular occasion, towards the end of a very dry summer 

 •(last year), the maximum signal distance between a certain ship and 

 station, 500 feet above the sea, was 38 miles, the usual distance having 

 previously been 68 miles. Two days later, during which time no 

 alterations whatever had been made to the adjustments of the instru- 

 ments, but which included 24 hours of heavy rain, the maximum 

 •distance obtained was 70 miles, which has since been maintained. 



Repeated experiments with and without earths on the transmitter 

 .and receiver have shown me that, in the open sea, signals may be 

 obtained up to 50 or 60 per cent, of the full distance, without earths 

 •on the receiver, though such a large proportion is unusual, the average 

 being 30 per cent. A condenser of suitable capacity acts nearly as 

 well as a good earth ; without an earth on the transmitter, the per- 

 centage <of distance has never exceeded 15 per cent. Using good 

 .earths., but no aerial wire whatever on the receiver, or near it, 

 .signals have newer been obtained over 3 miles. With no aerial wire 



