656 HENRY A. EOWLAND 



from the primary disturbance reaches the second coil, we perceive the 

 disturbance by means of the spark formed at the break of the coil. 

 Should I move the coils further apart, the spark in the second coil would 

 be somewhat delayed, but the distance of 185,000 miles would be neces- 

 sary before this delay could amount to as much as one second. Hence 

 the effects we observe on the earth take place so nearly instantaneously 

 that the interval of time is very difficult to measure, amounting, in the 

 present case, to only TT(nn j- 1 - {mro . of a second. 



It is impossible for me to prove the existence of this interval, but I 

 can at least show you that waves have something to do with the action 

 here observed. For instance, I have here two tuning forks mounted on 

 sounding boxes and tuned to exact unison. I sound one and then stop 

 its vibrations with my hand, instantly you hear that the other is. in vibra- 

 tion, caused by the waves of sound in the air between the two. When, 

 however, I destroyed the unison by fixing this piece of wax on one of the 

 forks, the action ceases. 



Now, this combination of a coil of wire and a Leyden jar is a vibrating 

 system for electricity and its time of vibration is about 10,000,000 

 times a second. This second system is the same as the first, and there- 

 fore its time of vibration is the same. You see how well the experiment 

 works now because the two are in unison. But let me take away this 

 second Leyden jar, thus destroying the unison, and you see that the 

 sparks instantly cease. Eeplacing it, the sparks reappear. Adding an- 

 other on one side and they disappear again, only to reappear when the 

 system is made symmetrical by placing two on each side. 



This experiment and that of the tuning forks have an exact analogy 

 to one another. In each we have two vibrating systems connected by a 

 medium capable of transmitting vibrations, and they both come under 

 the head of what we know as sympathetic vibrations. In the one case, 

 we have two mechanical tuning forks connected by the air; in the other, 

 two pieces of apparatus which we might call electrical tuning forks, con- 

 nected by the luminiferous ether. The vibrations in one case can be 

 seen by the eye or heard by the ear, but in the other case they can only 

 be perceived when we destroy them by making them produce a spark. 

 The fact that we are able to increase the effect by proper tuning dem- 

 onstrates that vibrations are concerned in the phenomenon. This can, 

 however, be separately demonstrated by examining the spark by means 

 of a revolving mirror, when Ave find that it is made up of many succes- 

 sive sparks corresponding to the successive backward and forward move- 

 ments of the current. 



