Mr. E. H. M. Bosanquet on Electromagnets. 537 



that the induction has been forced up to the high value of 

 18,500. 1 haA-e shown in recent papers that this quantity- 

 lias no fixed limit in bar-electromagnets. This accords to 

 some extent with the conclusions of Mr. Shelford Bidwell in 

 the paper before referred to. 



The table of experiments is followed by one containing the 

 means of the errors of the formulae Wi and W 2 for the groups 

 into which the experiments are divided. 



Finally there are set out a few experiments made with the 

 electromagnets not in contact, but separated to the distances 

 mentioned by slips of card and wood. These experiments are 

 not approximately satisfied by the foregoing formulae ; but 

 they would agree to some extent with W x if ; instead of the 

 coefficient 



8^981 =-° 0004056 ' 



we took about half that quantity, say '000026. The experi- 

 ments at distance '2 would require a formula of the type of W 2 . 

 At present I am unable to give any explanation of these 

 numbers. 



The general truth of the law 



Tension a SB 2 



is sufficiently established. 



In my theory of permeability I have assumed the tension 

 within the magnetic body a §E$. It is clear that this assump- 

 tion leads in that case to consequences which correspond with 

 reality, and that the assumption tension oc SiS 2 does not do 

 so in that case. I am at present unable to explain the diver- 

 gence between the two points of view. 



The weights have all been reduced to lbs. and ozs. to facili- 

 tate comparison with the actual experiments. 



Batteries were used for weights up to about 5 lb. ; the 

 dynamo from about 2 lb. upwards. 



