190 TENTH ANNUAL REPORT, ETC. 



space with a velocity which it is fearful to contemplate. ^ Huge as are 

 these masses of matter, and terrific as are their velocities, they are 

 perfectlv controlled by their Omnipotent Lord, v/ho subjects them to 

 those few and simple laws with which we all have to do in the actions 

 of every-day life. 



[Since the delivery, in January last, of this ingenious and interest- 

 ing lecture, the motions of the rotascope or gyrascope, as it is now 

 caUed, has unexpectedly become a subject of general popular interest, 

 and thousands of copies of a simple form of the instrument are now 

 manufactured to gratify the public curiosity. The explanation of the 

 principles of compound rotary motion is as old as the day of Newton, 

 and the experimental illustrations given in this lecture have been 

 annually exhibited by Professor Snell to his class in Amherst College 

 for upwards of twenty years. 



The following remarks may, perhaps, serve to make the brief ex- 

 planation of Professor Snell of the horizontal rotation a little more 

 easily understood. Suppose the horizontal axes (fig. 10) placed 

 north and south, and the wheel revolving towards the east, then the 

 particle A will tend to move eastward by the rotation and northward 

 by the action of gravity ; the resultant will therefore fall between 

 these two directions, but much nearer the former, on account of the 

 greater force. The tendency will therefore be to turn the plane_ of 

 the disk outward, which, on account of the fixed position of the point 

 B, must carry the point D backwards. The same statement may be 

 made with regard to the motion of the lower point of the disk, which 

 conspires with the upper to produce a motion of the system in the 

 same direction. 



An interesting application of the principle of compound rotation 

 has lately been made to the explanation of the lateral deviation of a 

 ball from a rifle-bore cannon. The deviation is always in the same 

 direction, and is the result of the same kind of action which produces 

 the horizontal rotation of the system exhibited in the experiment 

 (fig. 10) of the lecture. J. H.] 



