87 
the particles of magnetic bodies , &c. 
which the magnets revolve, it increases rapidly. The por- 
tions of magnetism destroyed, or rather whose developement 
is prevented in the disc by circular cuts, at the distances *7, 
i*s, i’7, 2-2 inches from the centre, appear, by these expe- 
riments, to be proportional to 94*9, 183-7, 360-7, 637-7. The 
last three numbers are very nearly proportional to the masses 
separated towards the centre, the quotients arising from 
dividing each by the square of the diameter of the section 
corresponding are 31-9, 31-2, 32-9 ; the mean 32-0; and the 
whole would have followed the same law, had the first num- 
ber been 63 instead of 95, which difference is not greater 
than might take place in repetitions of the observations where 
the whole number of revolutions of the disc is 7 or 8, as in 
this case. When the magnets revolved under the disc I, 
with their axes at the distance 3*2 inches from the axis of 
rotation, the same as in the present instance, the value of z 
was 1528-7 (Table II.), and when they revolved at the same 
distance under the ring whose diameters were 6-4 inches, and 
8*4 inches, its value was 160-5 (Table VI.); so that the 
quantity of magnetism whose developement was prevented 
by the removal of the disc diameter 6-4 inches, is proportional 
to 1368-2. Now, taking 32 as the quotient arising from divi- 
ding the number representing the quantity of magnetism 
destroyed, by the square of the diameter of the disc removed, 
1310-7 will represent the quantity of magnetism destroyed by 
the removal of the disc diameter 6- 4 inches. Supposing the 
law to be correct, the difference between this number, de- 
duced from the observations with the disc 2, and the preced- 
ing, deduced from those with the disc 1, is not very far 
beyond the limits of errors in the observations, even had they. 
