422 Mr. W. Brown on the Effects of Percussion and 

 Table II. — Dimensions of Magnets. 



Number of 

 specimen. 



Length of 



magnet, in 



centimetres, 



I. 



Diameter of 



magnet, in 



centimetres, 



d. 



Dimension, 

 ratio IJd. 



Weight of 

 magnet, 

 in grms. 



I 



10 



0-300 



33 



5-5 



II 



10 



0-265 



38 



4-3 



Ill 



10 



0-270 



37 



4-5 



The five pieces of each sample were then magnetized by 

 placing them between the poles of a powerful RuhmkorfF 

 electromagnet, which was excited by a current from twenty- 

 four Thomson tray-cells joined in series. The magnetizing 

 current was approximately 5' 3 amperes, producing a field of 

 900 C.G.S. units intensity. The field was measured by rota- 

 ting a coil of known dimensions between the poles of the 

 magnet and observing the deflection produced on a ballistic 

 galvanometer ; and this was reduced to absolute measure by 

 comparing with the deflection (on the same galvanometer) 

 obtained by rotating another coil of known dimensions in a 

 field the strength of which was known. 



When the field due to the electromagnet was being measured, 

 there was nothing between the poles except the measuring- 

 coil. In the process of magnetizing, the magnets were reversed 

 three times between the poles of the electromagnet and then 

 finally magnetized. This was also done in every case when the 

 magnets were remagnetized between two sets of experiments. 



After being magnetized the magnets were laid aside for a 

 period of eighteen hours, and then the deflections were taken 

 for the purpose of calculating their magnetic moments. They 

 were put through the same series of operations as the magnets 

 used in the former experiments, described in Part I. ; that is 

 to say, the deflection produced by each magnet on a magneto- 

 meter-needle was observed ; each was then allowed to fall 

 once perpendicularly through a height of 150 centimetres, 

 with the true north end downwards, on to a thick glass plate; 

 and the deflection on the magnetometer again taken with each 

 magnet in exactly the same position. Each was then allowed 

 to fall three times in succession through the same height, and 

 the deflection again taken. 



The following Table gives the results obtained for the 

 magnets when they were all glass-hard ; and also after they 

 had been magnetized and left undisturbed for a period of 

 eighteen hours. 



