Brown — Permanent Steel Magnets. 317 



Sheffield. The writer endeavoured to find out whether these tliirty specimens 

 were suitable for permanent magnets. After a good deal of preliminary 

 work only fourteen of them were found to give anything lilje satisfactory 

 results, and for tlie purpose of testing, these were all turned down to 0'3 cm. 

 diameter, and from 8 to 10 cms. long according to the material at command. 



In order to get the magnets made as permanent as possible, the method 

 suggested by Barus and StronhaU was adopted, viz. : — Make the nuignets 

 glass-hard, then place them in steam at 100° 0. for 20 hoars. Blagnetize them 

 as fully as 2iossible, and again heat them in steam for 5 hours. 



It was not convenient to steam the magnets for twenty hours continuously 

 but for three successive days they had 7 hours' steam and 14 hours' rest, or 

 21 hours' steam altogether. They were then magnetized in a magnetic field 

 of 2000 c.g.s. units, and again steamed for 5 hours, and when cooled they 

 were tested for tlie first time. 



The magnets were prepared, hardened, and tested in exactly the same 

 way as already mentioned with the Stubs' steel magnets. The first tests 

 were made on June 17th, about an hour after the magnets had been steamed 

 for the final 5 hours, and the other tests took place on the same date of the 

 succeeding months up to December. In the intervals between the tests, the 

 magnets were kept in a vertical position, away from all iron or other 

 disturbances. 



Table IV. gives the chemical composition of the magnets, and the results 

 of the tests for the first, second, and sixtli months respectively, as well as 

 tlie percentage loss in magnetic moment per gramme for six months. 



' Bulletin No. 14, 1885 ; Dept. of the Interior, U.S.A. Gedlogical Survey. 



[Table IV. 



