Description of the Rotascope. — 277 
Let a small rod extend from the upper piece of the frame, with di- 
visions marked to indicate the depressions and_-elevations of the cord. 
Give the frame and weights a rotation of any convenient velocity. 
The weights will spread out and describe a frustum of a cone, like 
the two arms of a mill governor; while the increased tension of the 
cords acting on the principle of the funicular machine, will elevate the 
weight placed at the centre. Note the height to which it rises, and 
the velocity of the weights. Bring the frame to rest again. The 
central weight will descend to its former level, but by adding weights 
to the end of the cord, it may be again brought up to the elevation 
which it had during the rotation. The sum of the weights required 
for this purpose, shows the centrifugal force. 
13. In addition to the experiments already detailed, the rotascope 
furnishes the means of making experiments on the friction of pivots 
and of verifying the results of other methods employed for that pur- 
pose. The mode of experimenting is, to attach to the moving cord, 
applied about the axis of the wheel, and passing over pullies, weights 
bearing certain known relations to each other. Thus we may apply 
ateach end of the cord, one fourth of a pound, cause these to descend 
three feet, uncoiling the cord, and giving a constantly accelerated 
motion to the wheel, until it quits the knob ; after which, the velocity 
acquired will be gradually diminished, until the wheel is brought to 
test by the effect of friction, and the resistance of air. Repeat the 
€xperiment, doubling, trebling, or using any other convenient multi- 
ple of the weights first employed. In each experiment, note care- 
lly, by a good timekeeper, the time elapsed from the moment the 
Wheel is first allowed to turn in obedience to the weights, till the 
Sting quits the axis, and also till the wheel again comes to rest. 
The first will enable us to ascertain how much more slowly the 
surface of the axis was moving at the maximum velocity of the wheel, 
than the weight would have moved, after falling the same distance by 
the full force of gravity. We shall thus know the absolute velocity 
of the wheel, and, of course, that of its centre of gyration may be 
ascertained. 
By the second, we shall be enabled to compare the effects of 
rent weights or forces, to discover the relation between the 
Weights themselves, and the times in which friction destroys those ef- 
fects, and possibly to establish some points in reference to the rela- 
of gravity to time and space respectively, and of friction, to 
Velocity. 
