D4 Mr. 8. C. Laws on the Magnetic Susceptibility 
of & calculated. For the force P acting on the metal cylinder 
situated half within and half without the coil, Boltzmann 
gives the value * 
ENEVC2p?mn 4 (2-+m?)(—6) 8 1(b?—B) 
Pe Ee [ Nie Lake Shee es pepe tee FS 2 | 
b—p Oe 3° (Pm? (6-8) 3 (C— me 
where kis the magnetic susceptibility, 2m the length, and p 
the radius of the rod ; / represents the length, ) the external 
and 8 the internal radius of the coil; N is the number of 
turns per cm. in each layer of the coil and v the number 
of layers ; C is the current passing through the coil. 
Also 
b+ Va 
pt yee 
mY i? isi 
aa m*(m? + 67)? — m?(m* + B?)2" 
The results obtained are shown below :— 
e=lo 
and 
Bismuth.—Radius of rod =*2908 ems. 
| Current | Field inside | Doflexion | Bores (in mil | Walla 
aa Se cout dive to due to grams) on cylinder of 
=O, current=H. pete: ee he kx 10°. 
| A a 
amps. 
14 183 34:3 ‘O57 13°8 
| 2 261 70:6 ‘118 13-9 
3 392 765 270 14o% aa 
| 4 528 133 ‘470 13-9 5 
5 653 212 750 141° 
6 784 119 1:05 13°8 | 
7 915 162 1:43 138 
8 1046 211 187 138 
9 1176 267 2-36 13°8 
10 1307 332 2-93 139 
} 
| 
| 
The mean of the calculated values of & shown in the last 
column: is 13°9 x 10-*: 
Using the same method, von Httingshausen found for three 
samples of bismuth the values 14°0x 10~°, 14:5 x 10-8, and 
13°5 x 10-8, whilst by three distinct methods the mean values 
he obtained were 13°6 x 10-6, 15°3 x 10-6, and 13°4 x 107°. 
Curie also has measured the magnetic susceptibility of 
* Boltzmann, Wien. Ber. 1\xxxiii. p. 581 (1881). 
+ Von Ettingshausen, Joc. cit. p. 272. 
