Mr. R. H. M. Bosanquet on Electromagnets. 303 



It will be noticed that the numbers of windings are not 

 exactly proportional to the linear dimensions. It was not 

 practicable to carry this out ; and of course it does not matter 

 whether a given number of current- turns is made up one way 

 or the other (by current or turns). 



In the first three entries of the bars with pole-pieces, the 

 initial discrepancies being very great, the means of selected 

 values were adopted. 



The discrepancies between the numbers in any one column 

 are those in which any deviation from the law of similars 

 would appear. While the values (particularly at beginning 

 and end) are capricious in the extreme, it is certainly not 

 possible to detect any systematic difference between the 

 numbers belonging to the large and small bars. 



Before proceeding to calculate with these numbers, I will 

 now exhibit in a small figure the nature of the relation between 

 the magnetic resistances due to 



(1) the permeability of the metal, as derived from rings ; 



(2) the bars with pole-pieces (P.P.); and 



(3) plain cylindrical bars. 



B 



5000 



15,000 



20,010 



The resistance in each case is supposed to be due to a length 

 of metal = 1 centim., and p is expressed in decimals of a 

 centimetre, though drawn to a different scale for convenience. 

 The lowest curve is made up of the values from rings E, F 



