NATURAL PHILOSOPHY. 1 *"> 



method adopted by Mr. Airy, of applying directly the theorem of the 

 composition of rotary motion ; as doubtless Newton would have done, had 

 it been known to him. But here, as in so many other instances, the first 

 explanation presented itself mixed up with more complex considerations ; 

 and, as has been well observed, "simplicity is not always a fruit of the 

 first orowth." To those not versed in the mathematical theory, of all 

 points in Physical Astronomy, the modus operandi of the Precession, 

 perhans, usually seems the most paradoxical, and the explanations given 

 in some of the best popular treatises are seldom found satisfactory, fol- 

 io win " 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 bar, a terrestrial globe be substituted, 

 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 transferrence 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 equinoc- 

 tial 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 celestial 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 a,nd 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 

 according to which, the whole machinery of the universe is so profoundly 

 adjusted. 



