120 Prof. Barlow’s Account of Experiments on the Magnetism 
zero to 180°, according to the situation of the needle; the dis- 
tance and the rate of motion being the same. In all cases, by 
reversing the motion of the shell, the deviation was reversed 
also ; so that if with the shell turning one way, the needle de- 
viated to the east, it deviated to the west when the shell was turn- 
ed in an opposite direction : And in all cases during the rota- 
tion of the shell, the needle preserved its deviating direction re- 
markably steady, viz. without any kind of oscillation or tremor ; 
but the moment the motion ceased, it returned to its original 
and true bearing. The effect produced was therefore temporary, 
and depended entirely on the velocity of rotation. These were 
all the deductions drawn from the first series of experiments, 
and as the steam-engines were not set to work again till nearly 
the end of January, no farther observations were made till tibout 
the beginning of February, when Mr Barlow, finding himself 
embarrassed with the iron-work of the lathes and other machines, 
had now an apparatus constructed, which he erected on his own 
premises, and by means of which he at length succeeded in de- 
ducing the laws which regulate and determine the direction of 
the needle in all cases, and in all situations. 
The results have been presented to the Royal Society, and 
they will, it is presumed, be published in the forthcoming vo- 
lume of the Philosophical Transactions. In the mean time, the 
following concise account of them may be acceptable to some of 
your readers. 
The apparatus referred to above, consisted of a frame resem- 
bling that on which the cylinder of an electrical machine is hung, 
the ball supplying the place of the cylinder ; the diameter of the 
ball or shell was eight inches, and its weight about 30 lb. A 
strong table was fixed with its feet into the ground, the floor of 
the room being cut away, so as to prevent any shaking of the 
floor or walls. The diameter of the larger wheel was 18 inches, 
of the smaller 3 inches, and the handle might be turned with 
ease twice in a second, which gave about 720 revolutions per mi- 
nute to the shell. 
A stand, made heavy by being loaded with sand, had a small 
platform attached to it, with a semicircular hole in its side, 
whereby it might be brought up close to the shell, and the com- 
