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. 
tis formed of two concentric rings revolving on axes at right angles 
toeach 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 immer 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 
‘op, 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 
'otake place. This end is most important in whatever concerns the 
Principles of mechanics. It is what constitutes the great beauty of 
‘twood’s experiments, that the action of gravity is made to coincide 
principle, with its actual operation when unrestrained ; while at 
€ same time the bodies submitted to its action move with velocities 
Which can be readily followed by the eye. 
li. Numerous facts in Geology strongly indicate that at some re~= 
Mote periods of duration, the position of the earth’s axis with regard 
‘othe 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. 
