OP ARTS AND SCIENCES. 333 



whicli it would finally have attained had the current not been cut off. 

 The third column expresses similarly the percentage magnetization 

 after different intervals of time at a distance of 14 inches along the 

 bar. The fourth column is taken from a table in Jenkin's " Electric- 

 ity and Magnetism," page 330, and expresses the percentage electrifi- 

 cation at the end of a cable, also in terms of an arbitrary unit. The 

 value of this unit for the French Atlantic cable is given as 0.196 

 seconds. The magnetic value of this unit for a distance of two inches 

 over our bar is 0,010 seconds, and for fourteen inches 0.013 seconds 

 nearly, or about one fifteenth of the electric value for the whole At- 

 lantic cable. From this an idea can be formed of the greatness of mag- 

 netic, as compared with electric, resistance. 



TABLE OF PERCENTAGE MAGNETIZATION AS DEPENDENT 

 UPON THE TIME. 



Of course it is not possible to expect close agreement of our results 

 with those obtained for electricity. It is true that every law of mag- 

 netic induction may be said to correspond to one in electric conduc- 

 tion ; and similarly we may expect that the laws of the establishment 

 of magnetic induction (propagation of magnetism) will correspond 

 to those of the establishment of the electric current. But we must 

 remember that a bar magnetized at one end really corresponds not to 

 a perfectly, but to an imperfectly, insulated cable, the laws for which 

 [ have not been able to find anywhere developed. The apparent 

 agreement of the third and fourth columns of our table at the ex- 

 tremes, and to so large an extent elsewhere, is certainly remarkable 

 whether accidental or not. 



The table shows that the form of the magnetic wave at a moderate 

 distance from the primary is similar to that of the electric wave at the 

 end of a long cable, but that as we approach the primary the round- 

 ness disappears, so that a rapid series of waves would present more 



