258 Mendenhall and Waidner — 



period was again determined ; magnets then pushed apart, etc. 

 The results are shown in the following table : 





T 



M 



Distance between 



Time of Vibration 



Magnetic Moment 



Centers of Magnets. 



of Disc. 



C. G. S. Units. 



o .9mm 



2-618 secs 



0-1251 



1-2 



2-718 



•1160 



3-2 



2-659 



•1212 



1-2 



2-725 



•1155 



3-2 



2-663 



•1209 



1-2 



2-727 



•1153 



3'2 



2-666 



•1206 



These experiments show that the first near approach of the 

 magnets produced a permanent decrease in the magnetic 

 moment amounting to about 4 per cent (this was to be expected 

 inasmuch as these magnets had not been aged). After that it 

 will be seen that the magnets practically regain their former 

 magnetic moment on separation. The temporary decrease in 

 magnetic moment due to mutual action is less than 5 per cent. 



A similar set of experiments with the shorter magnets, B 3 , 

 gave a decrease of 5*5 per cent due to mutual action when the 

 center lines of the magnets were l mm apart. When the mag- 

 nets were pushed together so that they touched their neighbors 

 throughout their length, the magnetic moment continued to 

 decrease for some minutes until the decrease amounted to 19 

 per cent, and on separating them they did not recover but were 

 permanently weakened about 10 per cent. 



Quality of Steel. — Under similar conditions magnets of 

 Jonas & Colver's special magnet steel* (probably tungsten steel) 

 have moments about 25 per cent greater than those made from 

 watch hair-spring, which is the next best material. 



Effect of Jars, etc. — Magnets B 3 , 4: mm long, dropped twenty 

 times though 30 cm on to a glass plate diminished only \ per cent 

 in magnetic moment ; with magnets B 3 , l mm long, the change 

 was less than 1 per cent. Boiling immediately after magneti- 

 zation reduces the moment by 10 per cent or 15 per cent, and 

 most of the loss occurs during the first few minutes of boiling. 



Paschenf has called attention to the fact that to increase the 

 sensibility, for a given period, we must increase the total mag- 

 netic moment M and decrease the moment of inertia, K. 

 Assuming that the magnetic moment is proportional to the 

 volume, i. e., for a given cross section proportional to the 

 length of the magnet, and that the inertia of the non-magnetic 



* From Boker & Co., N. Y, f Wied. Ann., xlviii, 282. 





