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 sura 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 

 at each 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 

 rest by the effect of friction, and the resistance of air. Repeat the 

 experiment, doubling, trebling, or using any other convenient multi- 

 ple of the weights first employed. In each experiment, note care- 

 fully, by a good timekeeper, the time elapsed from the moment the 

 wheel is first allowed to turn in obedience to the weights, till the 

 string quits the axis, and also till the wheel again comes to rest. 



.The Jijst 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 

 different weights or forces, to discover the relation between the 

 weights themselves, and the times in which friction desti'oys those ef- 

 fects, and possibly to establish some points in reference to the rela- 

 tion of gravity to time and space respectively, and of friction, to 

 velocity. 



