216 Mr. J. R. Ashworth. Methods of making Magnets 



intense hardness. In contrast with this it may be mentioned that 

 music wires are not at all hard, being easily touched with a file. 



In order to gain further insight into the cause of the negative 

 coefficient in these wires, some experiments were made to test the effect 

 of removing successively the outer layers of the wires by dissolving 

 them in nitric acid. This revealed the important relation that the 

 coefficient became more negative as the diameter became less, the 

 length remaining the same, that is to say, as the dimension ratio 

 increased. 



To verify this carefully a series of stout music wires of different 

 thicknesses, but in other respects as uniform as possible, were pro- 

 cured from a manufacturer at Warrington, to whom I am also 

 indebted for kindly supplying other samples of steel wire. The 

 results of these experiments are most conveniently exhibited in 

 tabular form, and are here annexed. 



Table III. 



No. 



cl. 



m. 



E. 



li. 





0. 



a. 



o-oo 



ax d. 



-oooo 



33 



0-216 



3-535 



55-3 



530-3 



428-5 



0-192 



-0136 



294 



30 



0-187 



2-590 



63-8 



592-8 



508-6 



0-142 



-0184 



344 



28 



0-174 



2 -235 



69-0 



632 -4 



551 -5 



0-128 



-0226 



393 



26 



0-153 



1-760 



78 -0 



736-0 



652-8 



0-113 



-0203 



310 



24 



0-134 



1-365 



89-0 



742 -0 



686 -3 



0-075 



-0306 



410 



Length of each piece = 12 cm. 



With the exception of No. 26 (and "No. 26 was anomalous in some 

 other respects) the coefficients become progressively more negative 

 as the dimension ratio increases. The increasing product of the co- 

 efficient into the diameter shows that the coefficient changes more 

 rapidly than the dimension ratio. The table also shows the regular 

 diminution of the permanent loss, /3, and increase of intensity as the 

 dimension ratio increases, relations which hold in further experiments 

 of the same kind to be described later on. 



Several of these wires after being thus tested were dissolved in 

 nitric acid, and the temperature coefficient determined at successive 

 stages of the process without any remagnetisation of the wire. The 

 results of No. 33 alone are here given, as they sufficiently exemplify 

 what generally takes place under these circumstances. The negative 

 character of the coefficient progresively increases with increase of 

 dimension ratio, and at a rather greater rate as in Table III. 



It is interesting to observe in these experiments the increase of 



