1907.] on Recent Contributions to Electric Wave Telegraphy. 085 



Electric oscillations are classified into highly damped, feel)lj 

 damped and undamped varieties corresponding to few, many and 

 infinite oscillations in a train (see Fig. 5). In electric- wave tele- 

 graphy we have various kinds of transmitters or wave-makers which 

 are intended to create these types of oscillation. In the. first case, if 

 we set up an antenna and connect the lower end to one of the spark 

 balls of an induction coil, the other being to earth, we have an 

 arran^i^ement which produces highly damped oscillations and waves 

 (see Fig. 6). This is due to the fact that since the capacity of the 



Fig. 6. 

 Antenna emitting Strongly Damped Telegraphic Electric Waves. 



antenna itself is small, the energy which can be stored up in it and 

 liberated at each spark discharge is also small, at most a fraction of a 

 foot-pound or a few foot-pounds. Hence it is rapidly frittered away 

 by resistance and in radiation, and the oscillations are few, say half 

 a dozen or so, and highly damped. If, however, we form an oscilla- 

 tion circuit consisting of a large condenser, inductance and spark 

 gap we can store up a larger amount of energy and liberate this 

 suddenly across the spark gap at each discharge (see Fig. 7). If, 

 then, these oscillations are made to induce others in a directly or 

 i nductively connected antenna, we can hberate the energy as radia- 

 tion, and having a larger store to draw upon create longer trains, say 

 of 20 to 100 more feebly damped oscillations. 



Corresponding to these types of transmitter there are various 

 suitable forms of receiver. With a highly damped radiator we must 

 use some form of wave-detector, such as a coherer, which is chiefly 

 affected by the first or maximum oscillation, and this must be inserted 

 i n a receiving circuit which is easily set in oscillation by a single or 

 a t most a few electromagnetic impulses. On the other hand this 



