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



The four last are comparable to Table vm., and give for ix, 



0-7571 

 0-7606 

 0-7577 

 0-7498 



mean = log-' (9-87912) = 0-7570 



The others are given in 



Table XIII. 



Here also the difference between the theory and observation is considera- 

 ble; more so than appears at first sight. The computed values of fj. given in the 

 eighth column assume that the intensity in every part of the magnetic circle is 

 equal ; or, in fact, that magnetism is transmitted by induction without any 

 diminution. That this is not the case is evident from comparing Nos. 55, 58, 

 and 33, in which the difference of sixteen inches in the two cylinders of the 

 magnet reduces the actual efficiency of the spires ofi> from 0-757 to 0-5765. 

 Therefore, all these calculated values are much too great, and yet all of them, 

 except the first, are less than those given by observation, while in the spirals 

 they are greater. 



The decrease of efficiency depending on an increase of the spire's diameter 

 is less than that assigned by theory, still more than in the spiral. In (F) and 

 (7?), which arc nearly of the same radii as (D) and (C), the ratio of /< is 0915 



