of the iron, as they were arranged by the lines of force from 

 the bullet, would counterad one another in their effects upon 

 C and D. Any inductive effeel from the iron would thus be 

 eliminated. Also the iron core could not be magnetized by 

 the current flowing in C and D since they are wound in the 

 same direction around each leg, contrary to what is done in 



F 



R 



U 



r 



E 



Figure 3. 



an electromagnet. The coils C and D contained 8000 turns 

 each of No. 34 enameled wire. All effects due to the presence 

 of the iron was thus eliminated, except the one effect men- 

 tioned above. In order to make communication easy between 

 the operators at the cannon and the observer at the galvanom- 

 eter, the apparatus was arranged as in Pig. 4. 



T 



L 



r<£h 



<1A 



R 



60 M&f-ers 



;=E 



■^■S'> 



L 



N '/ 



K\ N ' 



Figure i. 



The galvanometer was located at L in the testing labora- 

 tory and the transformer and cannon were placed in the base- 

 ment of a building, sixty meters distant, at I/. S and S' are 

 two double throw switches. N and .V are two telegraph 

 sounders, C and C two gravity cells, and K and K' two keys. 

 From the diagram it is easily seen that the switches can be 

 thrown so as to operate the telegraph instruments or so as to 



61 



