had the following dimensions: Length 15.5 centimeters, bore 

 1.3 centimeters. It was charged with 11 grams of black pow- 

 der, and a lead bullet weighing 17 grams. The galvanometer 

 G was located some 15 meters away from the cannon R, and 

 the coil C. A slight movement of the coil caused a small de- 

 flection of the galvanometer due to its cutting the lines of 

 force of the earth's field. Precautions were taken to see that 

 the coil did not move due to the discharge of the cannon. 



Under these conditions no deflection of the galvanometer 

 was produced, when the cannon was discharged over the coil. 

 It was immediately seen that any lines which might arise 

 around the bullet due to its motion, would not only cut the 

 coil at A, but also at B, and thus neutralize the effect produced 

 at A. In order to prevent this an iron core K was introduced 

 into the coil C. If any lines were to swell out from the mov- 

 ing bullet, and cut the coil at A, they would go through into 

 the iron. They would not be able to go on through the iron 



E 



R 



Figure 2. 



and cut the other side of the coil at B, because the iron is a 

 good conductor of these lines and they thus prefer the iron 

 path. 



Under these conditions on November 1, 1911, a strong de- 

 flection of the galvanometer was obtained when a bullet was 

 fired over it. This result was so strong that there was no doubt 

 as to its cause, and more extensive preparations were made in 

 order to study the phenomena. 



In order to eliminate any effects due to the iron itself, 

 caused by the magnetization of the iron, a closed core trans- 

 former shown in Fig. 3 was arranged. 



M is a core of iron, laminated as in a transformer. This 

 core is 18 centimeters long and 17 centimeters wide, outside 

 measure. Each leg is 2 centimeters wide and 3 centimeters 

 thick. The coils C and D were connected so as to oppose one 

 another, so far as the iron was concerned, so that any lines of 

 force swelling out from the bullet, cutting through the coils 

 C and D would set up a current in the same directions in the 

 coils ; and, so that any lines of force arising from the molecules 



60 



