the Magnetism of Basalt. oo 
value of H at the magnetometer-needle was taken as 0°12, 
and was obtained by vibrating a short magnet in the position 
occupied by the magnetometer, and at a place where H had 
been measured with a magnetometer somewhat after the Kew 
pattern. 
Employing the formula for the magnetic moment of the bar 
ay 
2 2 
vie a -tan 0, 
27 
and putting H="12, r=27°8 ems., \ (=half the pole-distance) 
—4-2 if we assume that the poles are 1 em. from the ends of 
the bar, and 

pena Lot cm. 
an w= 9 x 175° ems, 
“1227-82 —4-92)2 eC igh 
v= 12(27°8 42") xX bol _ xe 

2x27°3x2x175°5 
Hence, the volume of the. bar being 21°5 c.c., the intensity 
of magnetization is as =()'263, and the susceptibility 
=0°0057. 
Since the moment of the bar is proportional to the deflexion 
produced, and as all the bars were placed at the same distance 
trom the needle, subjected to the same magnetic field, and 
had the same length, with one exception, we shall not be far 
wrong in taking 3°6, the mean of experiments on two bars, 
as the magnetic moment per 20 mms. double deflexion. 
Employing this constant, the following values of K, the 
susceptibility, are found. 

/ } 
| 
Initial 
} 



) E K at 2 | Number of | 
Bar. Defiexion, |,,...*,,. | Kat end. | a Aes] 
ee Merete de. | beginning. | Heatings. 
Rowley Blue. mm. | 
BB atccih | 31-7 | 0053 | -Ou57 | One 
Ne ae ) O62 “0064 0025...) -Six ) 
| 
Rowley Dolerite. 
GE os oes 32-2 0058 ‘0013 One 
Lt ee o2'2 "0059 ‘0009 One 
) 
Dattenberg. . 
Na, 2 sah ee. 302 “0056 ‘0039 Two 
Nes See ween Td ‘VOLS U031 One | 
No. Sees 14-2 ‘0025 
Nos 4+ sea | 28°3 ‘0048 | 
No. Ope igee. ) 22°5 ‘0038 | 
Magnetite ...... 61:3 (H=3'6) 0166 ‘0126 One 


