189 
of Robison ball-ended Magnets. 
§ 3. The following results obtained by Messrs F. Phillips and 
R. Corless will illustrate the working of the method. The value 
H= 0176 gauss was assumed for the earth’s horizontal magnetic 
force. The ten distances were found to be as follows : — 
= 3066 cm. 
r 2 — 28-22 ,, 
16*49 „ 
>• 4 = 13-42 „ 
h x - 3-32 „ 
= 6'91 cm. 
p 2 - 8-22 „ 
p 8 = 5-68 „ 
Pi = 7-67 „ 
k 2 = 3-65 „ 
p^i -2 = 0-00735 cm. -1 
P-2 r 2~ 2 = 0-01032 „ 
p 3 r s ~ 2 = 0-02088 „ 
Pi r C 2 — 0"04258 „ 
Hence, by (1) 
m (0-02088 + 0-04258 - 0'00735 - 0-01032} = 0176 (3‘32 + 3-65) 
or 0-04579 m = 6’97 x 0-176. 
Thus m — 26'79 C.G.s. units. 
The value of m was also found by an ordinary magnetometer. The 
eight readings for 6 were 
41°-9 44° -0 44° -0 42°-0 
41°-5 43°-6 43°-6 42°-4 
the mean being 42° 52 ,- 5. The corresponding values of R x and 
Ro were 11 63 and 27‘26 cm. Thus 
Rr 2 = 0-007393 and R 2 ~ 2 = 0 001346. 
Hence, by (2) 
m (0-007393 - 0 001346) = 0176 x tan 42° 52' 5. 
Thus m = 27 03 c.G.s. units. 
This result is in good agreement with that obtained with the 
Robison magnetometer. 
The stem of the magnetometer magnet used in these experi- 
ments is formed of a knitting needle 0‘23 cm. in diameter. The 
spheres are formed of steel balls inch (1‘27 cm.) in diameter, 
their centres being about 1 5*7 cm. apart. The balls are first 
softened and then holes are drilled in them. They are then 
driven on to the knitting needle and the whole is magnetised in 
a coil. Further details are given in my earlier paper. 
