Projectile of Lead or other metal in the human body. 47 
in the interior of a wooden case furnished witb a handle. 
vibratory current from a galvanic battery traverses the 
primary coil, and the secondary circuit includes an ordinary 
telephone. Under these circumstances no sound is heard from 
the telephone, but if we cause any metallic body to approach 
the part (C) common to the two coils, the silence immediately 
gives place to a sound, the intensity of which will depend upon 
the nature of the metallic body, upon its form and upon its dis- 
tance 
We may remark in this connection that the most favorable 
form that can be assumed by the projectile for which we ex- 
plore, is that of a flat disk with its face parallel to the surface 
of the skin, and that the most unfavorable, a similar disk with 
its face perpendicular to the same surface. 
It is difficult in practice to obtain the exact adjustment of the ~ 
coils required, and it is therefore found advisable to introduce 
into the primary and secondary circuits respectively, two other 
coils (D and KE, fig. 2) analogous to the first, but very much 
2. : 
smaller, whose common surface can be modified by the play of 
a micrometer screw. By means of this fine adjustment we are 
able easily to reduce the telephone to the most complete silence. 
It should be added that the effects obtained, when a condenser 
(F) is introduced into the primary circuit, are much superior to 
those obtained without, as had been independently predicted 
by Professor Rowland of the Johns Hopkins University. 
_ If we wish to ascertain the depth at which the metallic mass 
lies embedded, this is easily ascertained if we know a priori its 
form, its mode of presentation and its substance. It is then 
only necessary to adjust the apparatus to silence while it is 
applied to the skin; after which removing the apparatus, we 
ring near it another metallic mass similar to that explored for 
