Brown — Permanent Steel Magnets. 



318 



Some results of experiments, published by H. Frank' in 1900, on 

 English silver-steel confirm the results obtained by T. Gray ; the author 

 also gives some interesting oyolic curves obtained by relating magnetic 

 moment and temperature. 



The first section of the present short paper gives the result of some 

 experiments in wliicli an attempt has been made to find the best length of 

 magnet to use for a given diameter, the same kind of steel being used 

 throughout, and in the same physical condition. By the best length is meant 

 that obtained from the dimension ratio which gives the highest magnetic 

 moment per gramme, for a minimum weight of material. 



For this purpose Stubs' tool steel was employed, a material the chemical 

 composition of whieli is not made public; but it can be obtained of eylinilrical 

 section in lengths of 33 cm. or so, and of diameter up to one centimetre or 

 more, of practically the same cross-sectional area throughout each length. 



Twelve different sizes of this steel were obtained, varying in diameter 

 from 0'16 cm. to 1"0 cm., and six magnets of each sample were made 

 varying in length from 15 cm. to 4 cm. 



The magnets were all submitted to the same heat-treatment, that is, they 

 were raised to a bright red heat in a gas muffie furnace, and tiien dropped 

 end on into 3 feet of water at 16°0., they were then cleaned up, measured, 

 and weighed, and magnetized in a magnetic field of 2,000 c.g.s. units. 



The magnetic moment per gramme, or specific magnetization of each, was 

 then carefully determined by means of the usual magnetometrie method. 

 The results for each set of magnets were then plotted in a curve, when the 

 abscissse represented tlie dimension ratio, and the ordinates the magnetic 

 moment per gramme. 



The values for one set of experiments are here given in Table I., and 

 shown as a curve in fig. 1. 



Table I. 



'Ann. d. Physik., Bd. ii., 1900, p. 19u, o38. 



8d2 



