414 



Prof. D. E. Hughes. 



[Mar. 6, 



1. Tube of thin soft iron, 2 centims. diameter, 20 centims. 

 4. ,, „ bundle of 1 millim. diameter soft iron wires 



-ti o 



Qj PI 



^2 



0) © 



1 Daniell 

 element. 



Eemaining magnetism on 

 ' cessation of the electric 

 current. 



218 

 960 

 458 

 1268 

 160 



106 

 29 

 18 



142 

 15 



7. Hard tempered cast-steel wire, 1 millim. diameter 



455 

 49 



105 

 16 



0-94 



109 



72 

 35 



8. Brass J 

 tube \ 



, „ { 



10. „ 



11. „ 



Electro -plated with f 

 iron extremely thin \ 



Electro-plated with iron 

 to t X q millim. thickness 



Ditto, 1 millim. thickness 

 „ 1 centim. 



3 centims. dia meter 

 20 „ long.... 



} „ . 



'.' . " 

 4 centims. diameter 



| 0-95 



idol 



401 

 1075 



still, this can be reduced far below that of the soft thin iron if 

 .sufficient thickness is allowed in order to produce the internal 

 reactions. This is shown in No. 3, where a solid 2 centims. diameter 

 of hard-cast steel has double the force of the thin soft iron under 

 polarising influence, and its remaining magnetism only 4 per cent, of 

 its previous force. This shows clearly that Jamin's views of the 

 superiority of thin steel bars over thick where permanent magnetism 

 is desired, are fully confirmed, as in order to have raised the cast- 

 steel 2 centims. thick bar to a high remaining magnetism, we should 

 have had to employ at least fifty times stronger inducing force than 

 that necessary for the thin bars. The proportion of remaining 

 magnetism in iron or steel to the inducing force is almost similar 

 throughout the entire range up to saturation, where the remaining 

 magnetism is no longer proportional to the inducing power, but 

 remains a constant, no matter how high and powerful the influence 

 excited. The molecules have simply then rotated to parallelism and 

 cannot rotate further without diminishing its force, and the sudden 

 •spring back to a partial neutrality is then the same for all forces 

 above that of saturation. The proportion of remaining magnetism to 

 that of its magnetic capacity under the influence of an inducing 

 field, is shown in Eos. 6 and 7, where iron and steel wires of similar 

 •diameter have not a wide difference, the remaining magnetism here 



