394 



Intelligence and Miscellaneous Articles. 



i iiro of about —60° C, loses a far greater percentage of its mag- 

 netism. In one case a bar magnetized to saturation lost 66 per 

 cent, of its magnetism. 



The low temperature was produced by solid carbonic acid and 

 ether; and the magnetic moments of the bar were measured by 

 placing it east and west of a suspended magnet which was provided 

 with a mirror. In this case we have the magnetic moment 



M= \ r 3 T tan </>, 



where >•= distance of magnet, T= horizontal intensity of earth's 

 magnetism, and <f>= angle of deflection of suspended magnet. The 

 angles were observed before the magnetic bar was surrounded with 

 the freezing-mixture and afterwards at intervals when it was sub- 

 jected, without removing it from its first position, to the influence 

 of the carbonic acid. The following Table shows the variations of 

 the deflections to which the magnetic moments are proportional. 



"When subjected to Freezing-mixture. 



Before 



^min. 



After interval 

 of 3# min. 

 f min. obs. 



1 min. 



2 min. 



5 min. 



freezing. 



observ. 



observ. 



observ. 



observ. 



•6390 



•6050 



•5860 



•5820 



•5790 



•5540 



•6395 



•6020 



•5850 



•5815 



•5740 



•5415 



•6390 



•6000 



•5840 



•5825 



•5700 



•5480 





•5980 



•5840 



•5815 



•5650 



•5480 





•5960 



•5830 





•5600 







•5950 



•5820 











♦5940 













•5930 













•5920 













•5910 













•5900 













•5890 











The zero of the scale was # 5000 ; and the observations are ex- 

 pressed in fractions of a metre. It will be seen that this bar lost 

 in forty-seven minutes nearly two thirds of its original magnetic 

 condition. After twenty-four hours' exposure to the temperature 

 at which it had been magnetized, its magnetic condition was 50 per 

 cent, of its original state. 



A ring of soft iron was next experimented upon according to 

 the method of Professor Eowland ; and it was found that its mag- 

 netic permeability, on being subjected to very low temperature, dif- 

 fered greatly from the results obtained for soft iron at ordinary 

 temperatures. 



It is well stated by Dr. V. Strouhal and Dr. C. Barus, in a 

 paper on the Physical Condition of Steel, Ann. der PhysiJc unci 

 Chernie, 1880, No. 13, that we must regard each bar of steel, in re- 

 gard to its magnetic condition, as an individual of special charac- 

 teristics ; and a long investigation will be necessary to determine 

 the limits of the effect of cold upon magnetism. — Silliman's Ame- 

 rican Journal of Science, April 1881. 



