and Inductance of a Concentric Main. 



533 





ber 10. 



bei 10. 



ber' 10. 



bei' 10. 



Kelvin 



1388405 



138840 

 138-840 



563704 

 56-370 



56-368 



51-373 

 51 -207 

 51-202 



135-23 

 135-31 

 135-29 



Mascart & Joubert . . . 

 Formulae 



Before the author worked out the approximate formulae, he 

 had verified Mascart and Joubert's corrections as far as four 

 figures by direct calculation from the series given in (5) and 

 (6) and the series obtained by differentiating them. As the 

 corrections to Kelvin's table when the argument is 15 and 

 when it is 20 are large, it will be interesting to calculate 

 these values by our formula*. 



Kelvin 



Mascart & Joubert 

 Formula; 



ber 15. 



-2969-70 

 -2967-20 

 -2967-26 



bei 15. 



■2952-33 

 ■2952-72 

 ■2952-66 



ber' 15. 



86-648 

 91-061 

 91010 



bei' 15. 



-4089-2 

 -4088-5 

 -4087-7 





ber 20. 



bei 20. 



ber' 20. 



bei' 20. 



Kelvin 



47583-7 

 474892 

 47491-6 



11500-8 

 1 14774-4 

 1147701 



24325-1 

 -43S02-8 

 -487979 



41491-5 

 111853 

 111853 



Mascart & Joubert ... 

 Formulae 





In evaluating the formulae we have only used 7-figure 

 logarithmic tables. To compute ber' 15 correctly we ought 

 to have calculated ber 15 and bei 15 to eight significant 

 figures, as ber 15 and bei 15 are nearly equal to one 

 another and from (24) we see that ber' 15 is nearly equal 

 to their difference. It will be seen that the accuracy of 

 Mascart and Joubert's corrections is satisfactory. The 

 values, however, they give for the functions when the 

 argument is 30 are not correct. 



