1854.] OF THE ROYAL INSTITUTION. 399 
given in some of the best popular treatises are seldom found satis- 
factory, following as they do the letter of Newton’s illustration and 
omitting the direct introduction of the principle of composition, 
which, if only from what has been here offered, is at once seen to 
be easily capable of the most elementary explanation. Indeed it 
was from this consideration forcing itself on the mind of the author, 
in several courses of popular lectures on Astronomy, that he was 
led to seek the means of experimental illustration above described ; 
and which would more palpably imitate the phenomena to the eye, 
if, instead of the rotating dar a terrestrial globe be substituted (as in 
Bonenberger’s instrument) —for better illustration made protuberant 
at the equator,— where the weight at the south pole acts the part of 
the sun’s and moon’s attraction, to pull down the protuberant matter 
of the spheroid at the equator if at rest, but when combined with 
the earth’s rotation results in a transference of the position of its 
axis, or slow revolution of its pole round the pole of the ecliptic in 
a direction opposite to its rotation, carrying with it the equinoxial 
points, and causing the signs of the zodiac to shift backwards from 
their respective constellations. 
It always affords a sort of intellectual surprise, to perceive for 
the first time the application of some simple and familiar mechanical 
principle to the grand phenomena of astronomy: to see that it is 
but one and the same set of laws which governs the motions of 
matter on the earth and in the most distant regions of the heavens ; 
to find the revolution of the apsides in a pendulum vibrating in 
ellipses, or the conservation of areas in a ball whirled round by a 
string suddenly shortened: or (as in the present case) to perceive a 
celestia] phenomenon, vast in its relations both to time and space 
and complex in its conditions, identified, as to its mechanical cause, 
with the rotatory movement of a little apparatus on the table before 
us,— or to discover the Precession of Equinoxes in the deviation of 
a rifle or a boomerang. And the simple experimental elucidation 
of such phenomena and their laws will not be useless, as it tends to 
confirm in the mind of the student the great characteristic of the 
modern physical philosophy first asserted by Galileo, the identity 
of the causes of the celestial and terrestrial motions, and to aid and 
elevate our conception of those grand and simple principles accord- 
ing to which the whole machinery of the universe is so profoundly 
adjusted. 
[Bi PA 
