328 Mr. T. Gray on the Experimental Determination 



was only 20'22, and that of the blue-tempered magnets little 

 more than half of this amount. 



With regard to the permanence of the magnets employed 

 in the first series of experiments, their magnetic moments 

 were found to be very little, if at all, changed by lying nine 

 months undisturbed in the laboratory. When newly magne- 

 tized, the glass-hard magnets lost about 2 per cent, of their 

 magnetic moment when allowed to fall three times with true 

 north pole down from a height of 70 centimetres to a hard 

 paving-stone. Blue-tempered magnets by the same treatment 

 lost 10 per cent. After lying nine months, the glass-hard 

 magnets when allowed to fall three times as just described, 

 lost 0*5 per cent, of their magnetic moment, blue 2*8 per 

 cent. 



The same magnets were then remagnetized and again 

 allowed to fall as before. The magnetic moment, which had 

 been but little increased, was found to be diminished in the 

 case of those tempered glass-hard by 1*7 per cent., and in the 

 case of those tempered blue by 4*4 per cent. 



Description of 

 temper. 



No. of 

 magnet. 



First magnetization. 



Second magnetization. 



Total 

 magnetic 

 moment. 



Magnetic 

 moment 



per 



gramme 



mass. 



Total 

 magnetic 

 moment. 



Magnetic 

 moment 



per 



gramme 



mass. 



Heated to bright^ 

 redness, and | 

 plunged in 1 

 water at about | 

 15° C. (Glass- 

 hard.) , 



1. 



2. 

 3. 

 4. 

 5. 



20-496 

 20-551 

 20-551 

 20-291 

 20-328 



72-296 



71-857 

 72-235 

 71-322 

 71-415 



21-129 

 21-204 

 21-129 

 21-185 

 21-073 



74-529 

 74140 

 74-296 

 74-464 

 74-201 



Mean 





20-44 



71-82 



21-14 



74-33 



Glase-hard, re- I 

 heated to 100° J 

 C, and cooled j 

 in air. 



6. 

 7. 

 8. 

 9. 

 10. 



21-054 

 20-568 

 20-869 

 20-869 

 20-308 



76-566 



75-897 

 75-887 

 75-203 

 74-651 



21-304 

 21054 

 21-258 



21-285 

 20-626 



77-477 

 77-660 

 77-275 

 76-670 

 75-800 



Mean 





20-73 



75-64 



21-10 



76-98 



Glass-hard, re- 

 heated to 150° 4 

 C. and cooled' 

 in air. 



11. 

 12. 

 13. 

 14. 



15. 



20-496 

 20-681 

 21-092 

 20-253 

 20-421 



76-107 

 76032 

 76-696 

 74-323 

 74-834 



20-663 

 21-017 

 21-296 

 20-701 

 20-504 



76-675 

 77-265 

 77-440 

 75-962 

 75175 



Mean 





20-59 



75-60 



2073 



76-50 



