694 Professor J. A. Fleming [May 24, 



respect in the case of undamped waves, but we are still awaiting 

 quantitative confirmation. Amongst other assertions it has been 

 stated that the undamped waves are less easily " tapped " to use the 

 ncAvspaper expression. This is a fallacy. With the proper experi- 

 mental appliances a receiving circuit can Ije gradually adjusted to any 

 electrical frequency, and when it comes to the right frequency it must 

 be affected just as much as true receiving stations for which the 

 waves are intended. It is all a matter of apparatus and skill. To 

 illustrate the first point, viz., the effect of the nature of the receiving 

 circuit we may take an instance from optics. When we look through 

 a telescope at the stars we can see a certain number down to some 

 limiting magnitude. No amount of prolonged gazing when using the 

 eye as a wave receiver increases the effect produced by a just invisible 

 star. If, however, we use a photographic plate the effect on it is 

 cumulative, and we can by a sufficiently long exposure obtain im- 

 pressions of invisible stars in countless numbers. The photographic 

 film is a wave detector of quite a different kind to the retina. In the 

 case of the film it can make up by time what is wanting in intensity 

 in the wave motion. In the case of wireless telegraphy it is clear 

 therefore that- the nature of the receiver has a great deal to do with 

 the possible advantages of undamped waves, and it is not merely a 

 question of the tuning or the transmitter.* Again the ordinary 

 10 -inch induction coil and spark transmitter as used on ships takes 

 up ^ of a horse-power w^hen in full work, and can send wireless 

 messages 200 miles or more when an appropriate receiver is used. 

 I find it very difficult if not impossible to obtain sufficiently high 

 frequency oscillations by the arc method unless at least 1 or 1^- 

 horse-power is being expended in the arc. Hence for short distance 

 work on the point of economical working as well as simplicity of 

 apparatus and ease of working the spark method has advantages 

 denied to the arc. We were told not long ago by an eminent elec- 

 trician that the arc method of creating undamped waves sounded the 

 death knell of spark telegraphy. It is always advisable to exercise 

 some caution in issuing obituary notices of well tried inventions prior 

 to their actual decease, and in this case although the power to create 



* In order that he may take the utmost advantage of the principle of 

 resonance, Mr. Poulsen uses in the receiver a device he calls a " ticker." This 

 serves to keep the condenser-inductance circuit of the receiver closed, until 

 resonance has exalted the oscillations to the utmost. The ticker then opens 

 it at intervals and inserts the particular oscillation detector, whether electro- 

 lytic or othci-, which makes the audihle or visible signal. In his syntonic 

 receiver Mr. Marconi has always adopted a similar plan for he keeps the 

 coherer terminals joined by a condenser which closes the secondary circuit of 

 the receiving jigger. A point of interest not yet considered is whether we do 

 need absolutely undamped waves to gain all the possible practical advantages 

 derivable from them. It may be that very slightly damped trains containing 

 say 50 oscillations per train and following each other several hundred times 

 per second will with an appropriate receiver give us all that we can obtain 

 from the use of forced undamped waves. 



