Perkins — Velocity of the Propagation of Magnetism. 173 



10 8 v / '2E * 2 



10*1 6 CIU , and Q is found from the equation Q = , 



where E = 12*9, n — 500, w = 377. and Q is the average value 

 of the flux at the center of the exciting coil. Hence -k- = — 

 Q o/3e - * = _ 6 i^X -16 = 193 _ F . nally C;b = _ g^ = 



-— -, the negative sign vanishing because -~— is negative. 



6 



90 O 

















300 













1 





700 



PERME 

 OF MA 



RMEA 

 /fZ7 7 



B/UT 

 VOL v 



y cut 



ST£E 



L 



/ 





600 

















SOO 

















4-00 

















300 

















ZOO 





/ 













/OO 



/ 















/ 



2 



3 



* 



s 



& 



7 



3 



The average flux density at a point four inches from the 

 center is 522 lines per square centimeter, obtained similarly to 

 Q above, and the permeability at this density was found to be 

 110, as shown in the permeability curve of the bar used.* This 



gives the reluctance per unit length as w m — - A ^qq '•> ^'83 



being the cross section of the bar. 



We are now in a position to make the final calculation, em- 

 ploying equation (5) and solving it for 7, which is equal to 



y/~F 



V m w m- ^ e have 



•0513 and v== - = 7336 cm / sec or 



* The author owes sincere thanks to Messrs. E. E. Moran and D. H. Miller, 

 students in Yale University, for the determination of the BH curve of the 

 steel bar. 



