_ 278 Description of the Rotascope. 
The perfection of the workmanship on the pivots and their bear- 
ings, will also be tested by this means, and it will be seen whether 
both ends of the arbor be finished with the same exactness. The 
friction on one end may, for the purpose of these experiments, be 
increased in any moderate degree, by furnishing that end with a 
small ring to form a bearing, through which the conical end of the 
shaft forming the pivot, may pass, and in which it may rest instead 
of resting and rubbing solely on the point. This ring will increase 
the moment of friction, by carrying the rubbing surface of the shaft 
farther from the mathematical axis of rotation. 
The following table presents the results of experiments made by 
means of weights of various magnitudes employed to produce rota- 
tion and shows the times in which the friction of the pivots, brought 
the wheel to rest ; the axis in each experiment being kept vertical 
as long as the motion continued ; but reversing the ends in the two 
separate series. The first column indicates the weights appended 
to the cords at each trial; the second, the number of seconds from 
the instant the motion commenced to that of its actual cessation. The 
third shows the ratios of the times observed with the several weights 
compared with the time required to bring the wheel to rest after it 
had been set in motion by one pound weight. The fourth column 
exhibits the square roots of the numbers of pounds. The fifth con- 
tains the differences between these roots and the aforesaid ratios, 
marked + when the root is greater than the ratio, and — when te 
reverse is true. * The sixth column contains the number of seconds 
in which the wheel would have come to rest on the supposition that 
the continuance of motion is precisely as the square roots © the 
weights which produce it. 
The departure of these numbers from the observed umes is great 
er in the higher velocities than in the lower, owing, obviously, to the 
greater resistance of the air in those cases. But in no instance does 
the experimental differ from the theoretical result by more than ten 
seconds. This is shown in the last column. 
It mast be observed that in all the experiments the weights de- 
scended through precisely the same distances, and of course Adovel- 
oped from the axis the same number of spirals of cord before it seerade 
tre quitted the knob over which it had been doubled. We might re- 
peat the operations, using all the different weights with differen! 
heights. Ingenious persons will find much interest in experiments 
of this nature. 
