Description of the Rotascope. 273 



When the wheel is to be stopped, it is most convenient and safe to 

 do it 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- 

 ing out of the hands. 



2. Suspend the detached ring and wheel, used in the first experi- 

 ment, to a cord attached to die ceiling above, by one end ; give the 

 wheel a rapid rotary motion, then give it an oscillatory motion through 

 an arc of sixty or eighty degrees. Different points of attachment may 

 be assumed, by which to connect the cord with the ring. If connect- 

 ed at a point opposite to one end of the axis 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- 

 sition, will be accompanied by a regular horizontal motion, opposite 

 in direction to that which the wheel would then have if it hung in 

 the position which it would take when at rest. 



3. Connect with the ring, at a point opposite to the axis of the wheel, 

 a wooden rod of sufficient strength to bear the weight when held hori- 

 zontally, and from nine to twelve inches in length. Attach the end 

 of this rod, remote from the wheel, to a cord suspended from the 

 ceiling. Set the wheel in rapid motion, and then bring it tip, so that 

 the rod shall be horizontal. Then suddenly abandoning it with the 

 hand, the cord will sustain it as before, but instead of hanging ver- 

 tically down, the axis of the wheel, and the rod, (which may be re- 



VoL. XXL— No. 2. 35 



