504 



The Rev. T. R. Robinson's Experimental Researches on the 



P + V + V 

 we have 



(6) 



wliich is sufficient for practice. I take or = 10 or 20, and thus obtain the value 

 of the integral very rapidly. This must no-vv be integrated for c, -which admits 

 of two cases. In the first the current is a circle whose radius = b, therefore 

 \dc = 2-nh ; and if 5 = the simi of the series in (4), the action of a single ring or 

 convolution of a spu-al, whose plane is perpendicular to the axis. 



M = ixF.A.Sy.2mh. (7) 



No sensible error can arise from considering it a circle ; and I have computed 

 the following table of the coefficient oi p. . F . A for the magnet and spirals 

 which I use, in which r = 1, and the least value of 6= 1.13. 



Table I. 



