248 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



due to those lines of magnetic induction which thread through the 

 centrally placed coil A^Az and do not also pass through the coil C1C2, 

 provided we neglect the lengths A1A2 and C'l C^ of the secondary coils 

 in comparison with the distance AiCi between the two coils. In 

 other words, the ballistic throw measures the magnetic leakage be- 

 tween the coils which are connected in opposition. When the con- 

 nector is placed across from A to F, then we get simply the throw 



Figure 23. 



Curves showing variations in the distribution of magnetic induction in rod 

 No. II. D = 1.905 cms. and m = 240. The ordinate-axis represents percentage 

 of magnetic induction. 



due to the whole magnetic flux of induction through the central coil 

 A-^Ai'va. precisely the manner which was used in all of the preceding 

 work on magnetization curves for different in'.s\ 



In this work on the distribution of the magnetic induction the extra 

 resistance which had to be thrown into the galvanometer circuit by 

 means of the resistance box R' in order to regulate the throw, varied 

 greatly. For a connection like that shown in the figure usually no 

 extra resistance was needed ; in fact for low as well as for high magne- 

 tizing fields the magnetic induction approaches uniformity, so that in 

 either case the ballistic throw is very low. Thus while in a certain 



