J. Trowbridge—Effect of Great Cold upon Magnetism. 3817 
490. This represents a loss of less than four per cent. In 
my experiments the magnetic bar magnetized at 20° C. when 
subjected to a temperature of about —60° C. loses a far greater 
percentage of its magnetism. In one case a bar magnetized to 
saturation lost sixty-six per cent of its magnetism 
he 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 pro- 
vided with a mirror. In this case we have the magnetic moment 
M=—r'T tan Pp 
When subjected to freezing mixture. 
Before min, Afterintervalof 1min. 2min. 5 min. 
freezing. Obsery. 814m. 16m.obs. obser. obser. obser. 
6390 “6050 *6860 “5820 ‘5790 3) 
"6395 “6020 “5850 *B815 5740 “65156 
“6390 6000 584 5825 5700 5480 
5980 *5840 “6815 5650 5480 
5965 *683 5600 
5950 “5820 
5940 
5930 
“5920 
“5910 
5900 
5890 
The zero of the scale was ‘5000 and the observations are 
expressed in fractions of a meter. 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 con- 
dition was fifty per cent of its original state. 
A ring of soft iron was next experimented upon according 
to the method of Professor Rowland, and it was found that its 
Magnetic permeability on being subjected to very low temper- 
ature differed greatly from the results obtained for soft iron at 
ordinary temperatures. 
It is well stated by Dr. V. Strouhal and Dr. ©. Barus, in a 
paper on the physical condition of steel, Ann. der Physik und 
Chemie, 1880, No. 18, that we must regard each bar of steel, 
1D regard to its magnetic condition, as an individual of special 
Cbaracteristies—and a long investigation will be necessary to 
determine the limits of the effect of great cold upon magnetism. 
