EFFECTS OF ELECTRICAL WAVES 487 



If now the preparation is so placed with reference to the 

 spark discharge that a contraction is just rendered impossible 

 during the passage of the spark, a contraction can again be 

 brought about when a mirror SS (Fig. 142) is so placed 

 that one end of it is near that sphere of the discharger 

 which is farthest away 

 from the preparation, while 

 the other end of the mirror 

 is near that end of the prep- 

 aration which is directed 

 away from the spark dis- 

 charge. The explanation 

 of the effect of this mirror 

 is very simple. A distribu- 

 tion of the electricities is 

 also induced in the mirror, and this induction must increase the 

 distribution of the electricities in the nerve-muscle preparation. 

 But it might be imagined that we are in this case dealing 

 with the effects of waves which are reflected by the mirror. 

 That this is not the case, but that we are dealing with the 

 effects of a double induction, is proved by the following 

 experiment. Let everything be left just as in the previous 

 experiment, only the spark discharge be turned through an 

 angle of 90, so that it is now vertical instead of horizontal 

 as before. The electric waves will now be reflected by the 

 mirror just as before, but the strengthening effect of the 

 induction through the mirror can now no longer exist. 

 Under these circumstances no contractions occur, whereby 

 it is proved that the electric waves are not the cause of the 

 mirror effect. Since my first publication of this experiment 

 I have supplemented it in two directions which make it more 

 interesting as a demonstration experiment, and which bring 

 additional proof of the correctness of our explanation. First 

 of all I have found that it is not necessary to use a metallic 



