Description of the Rotascope. 273 
_ When the wheel is to be stopped, it is most coavenient and safe to 
doit by applying a moderate friction with the thumb and finger to the 
axis, which will very soon effect the purpose. 
_ To set the wheel in rapid motion, apply the cord around the axis of 
the wheel, doubling it for that purpose, and putting the fold at the cen- 
tre, over the small pin near the end of the axis; having wound up the 
cord, take one end in each hand, and draw the two ends apart with 
suitable force, in direction at right angles to the axis, and, as near as 
may be, in the plane of the first circle, as well as parallel to that of the 
wheel itself. It will prevent breaking or chafing the moving cord at 
the pivot, to relax the strain when within two or three coils of the pin. 
The following are among the experiments which may be perform- 
ed by the aid of the rotascope. 
1. Remove the wheel and the brass circle 1, from the other parts; 
give the wheel a rapid motion on its axis, and holding the brass ring 
at some convenient opposite points of its circumference, carry it for- 
wards or turn the body round, holding it out so as to describe a small 
curve. The effort to change its plane of motion will be surprisingly 
Vigorous, and require some care to prevent the apparatus from leap- 
mg out of the hands. 4 
2. Suspend the detached ring and wheel, used in the first experi- 
ment, to a cord attached to the ceiling above, by one end; give the 
wheel a rapid rotary motion, then give it an oscillatory motion through 
uate of sixty or eighty degrees. Different points of attachment may 
be assumed, by which to connect the cord with the ring. If connect- 
ed ata point opposite to one end of the awis of the wheel, the latter 
may be raised up so as to form an acute angle with the suspending 
Cord ; the oscillatory motion, being given while the axis has this po- 
‘tion, will be accompanied by a regular horizontal motion, opposite 
direction to that which the wheel would then have if it hung in 
© Position which it would take when at rest. 
8. Connect with the ring, at a point opposite to the axis of the 
‘Wooden rod of sufficient strength to bear the weight when held hori- 
‘ontally, and from nine to twelve inches in length. Attach the end 
ofthis tod, remote from the wheel, to a cord suspended from the 
Wig: .Set- the wheel. in rapid motion, and then bring it up, Re that 
the rod shall be horizontal. ‘Then suddenly abandoning it with the 
Bnd, the cord will sustain it as before, but instead of hanging ver- 
Wally down, the axis of the wheel, and the rod, (which may be re- 
OL. XXI.—No, 2. 35 
wheel, 
