Description of the Rotascope. 269 



8. The use of a fly-wheel to regulate the motion of machinery 

 in a steam boat was formerly very common, and some of our boats 

 still retain it. In describing a curve with the boat, as in rounding to, 

 near a wharf, or in tacking rather shortly, a close inspection of the 

 wheel will show that a powerful effort is made by it to depress one, 

 and elevate the other of its gudgeons ; and that a correspondent effect 

 in racking the boat, or causing it to careen, is produced. 



9. A small apparatus said to have been devised by the celebrated 

 La Place to illustrate the precession of the equinoxes, has been made 

 in France, and imitated by an ingenious mechanic of Philadelphia. 

 It is formed of two concentric rings revolving on axes at right angles 

 to each other. Within the inner ring is a small sphere loaded at one 

 of its poles in such a manner as to produce a rotation in the axis of 

 the inner ring, when the sphere is caused to revolve with rapidity. 

 The chief parts of the rotascope had been devised and constructed 

 before I had an opportunity of seeing the above described apparatus. 



10. Several ingenious experiments were some time ago contrived 

 and executed by Mr. R. Tyler, a skillful mechanician of Philadel- 

 phia, with an apparatus resembling, in some respects, the common 

 top, included in a ring, and placed on a whirling table. 



In that arrangement, his experiments coincided, to a certain extent, 

 with some of those which are presented with the rotascope on the 

 orbit-rod. — There was wanting however the means of developing 

 and exhibiting the causes which produce the changes, actually seen 

 to take place. This end is most important in whatever concerns the 

 principles of mechanics. It is what constitutes the great beauty of 

 Atwood's experiments, that the action of gravity is made to coincide 

 in principle, with its actual operation when unrestrained ; while at 

 the same time the bodies submitted to its action move with velocities 

 which can be readily followed by the eye. 



1 1 . Numerous facts in Geology strongly indicate that at some re- 

 mote periods of duration, the position of the earth's axis with regard 

 to the plane of its orbit was different from what it is at present, and 

 that successive periods of change have at length brought it to its 

 present angle of inclination. 



12. It has been observed by Biot and other astronomers as " one 

 of the most remarkable phenomena of our system," that the motions 

 of rotation of all the planets are directed from west to east, like their 

 progressive motions ; and this agreement they have generally attribu- 

 ted to the first cause which determined the planetary motions. 



