Permanent Magnets. 



189 



net at the point indicated. In these columns two values are 

 given for the middle point of the magnet, calculated from the 

 two ends, and serve to indicate the degree of accuracy attained. 

 The second and third columns, from which all the others are 

 calculated, give the means of at least five or six separate deter- 

 minations which agree well among themselves. The results 

 were further checked by slipping the coils from the middle of 

 the magnets clear off each end at both temperatures. The 

 variation between this measurement and the others was always 

 less than one half of one per cent. This was considered quite 



good, as it was impossible to slip the coils over this whole dis- 

 tance as quickly as they were slipped over the small divisions. 

 In figures 3 curves for magnet A are given as follows : AA is 

 the distribution curve at 14° C. BB is the distribution curve 

 at 99°*5 C. CC is a curve showing the change in distribution 

 due to change in the temperature (14° — 99°*5 C). The scale 

 of ordinates is ten times that in A A and BB. EE is a curve 

 giving the induction in the magnet at 14° C. FF is a curve 

 giving the induction in the magnet at 99°*5 C. 



The tables on pages 192 and 193 together with the curves for 

 distribution give us sufficient data to calculate the magnetic 

 moments of the magnets A and B at both temperatures. In 

 the tables we are given n, the number of lines of induction 

 issuing from little divisions of the bar throughout its length, 

 as well as the distance d of these divisions from the center of 

 the magnet. A first approximation to the moment is given by 

 the formula 



