EFFECTS OF ELEOTRICAL 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 91 
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- 2 2 @ 
tion of the electricities is FIG. 142 
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 
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