268 Description of the Rotascope. 



axis, which of necessity winds up the supporting threads, into a spi- 

 ral about the axis. When wound up, the whole is placed in a tall 

 glass air-pump receiver, open at both ends and furnished with a 

 plate, collar of leathers and hook at the upper end. This receiver 

 is a frustum of a cone, and so large as to allow the wheel to run 

 freely up and down without interfering with the sides. Having ex- 

 hausted the air, the wheel previously wound up is detached from a 

 hook that had prevented its descent and revolves slowly at first, and 

 increasing in velocity according to the law of gravity, reaches at 

 length the extent of the cords, and being arrested in its downward 

 progressive motion at the moment it has arrived at the maximum ve- 

 locity of rotation, begins at that moment to wind up the cord in the 

 opposite direction about the axis ; while the whole wheel necessarily 

 rises and at length reaches to very nearly the same height as that 

 from which it had descended, when its momentum being lost, it again 

 descends, and so continues to do for many minutes, until the mere 

 rigidity of the cord has gradually destroyed all the momentum due 

 to the first descent. I had frequently observed, when performing 

 experiments with this apparatus, both in vacuo and in air, that by 

 swinging the wheel while ascending or descending, there was a de- 

 cided tendency to a particular arrangement in respect to the position 

 pf its axis, compared with that of the direction of oscillation. 



5. A carriage is often overset in turning a corner, or describing 

 a curve of short radius. Here the effect is produced sometimes with 

 astonishing suddenness ; at other times the inner wheel, or that which 

 according to the direction of the turn, is describing the smaller cir^ 

 cle, rises from the ground and revolves for a second or two on its 

 axle without touching the surface ; and, if the motion be not too 

 rapid, may possibly return and allow the vehicle to recover its posi- 

 tion, and pursue its course. But if the wheel which is revolving in 

 sir have any considerable velocity, the body of the carriage will ap- 

 pear to be overset by a force greatly superior to that which is due to 

 the mere centrifugal motion of the carriage from its curve. 



6. A disk of metal or other heavy substance, when projected into 

 the air by the hand, receiving at the same time a rapid rotary motion, 

 will sometimes be observed to perform singular evolutions in certain 

 parts of its track. 



7. The accurate experiments of Mr. Hutton and others, on gun- 

 nery, have proved that a very great deflection of a cannon shot, from 

 the direction of the piece, often takeS place, amounting in some in- 

 stances to an angle of about 15°. 



