The Philosophical Enquirer No. XXL 



212 



balance one aiiotliei, and though the 

 5um of the re-actions might not be so 

 great as though the planets were a 

 fixed mass, yet the results would pro- 

 duce an orbit nearly circular. 



We find, however, that upon the 

 earth, the fluids arc not equally dis- 

 tributed, and that there is a great pre- 

 ponderance in the southern hemisphere. 

 On examining a terrestrial globe, it will 

 be seen that when in the tropic of 

 Cancer the sun passes vertical in a 

 diurnal revolution over 200 degrees of 

 land ; but when in Capncorn, over not 

 more than 90 degrees. Hence the 

 earth's re-action is necessarily less at 

 the former time than at the latter; and 

 accordingly we find that it is then in 

 its Aphelion, and in the latter sign, 

 in its Perihelion. 



The continents of Asia, Africa, and 

 America present masses of uniform re- 

 action, when the sun is in Cancer, with 

 a diminished operation of their naiTow 

 seas ; whereas, when the sun is in Ca- 

 pricorn, the waters of the expanded 

 seas oscillate or re-act against the solar 

 impulses, the orbit is dimiuished, and 

 the oscillations combine to augment 

 the rotatory motion, which effects in- 

 crease till the declination diminishes, 

 when the re-actions of the narrower seas 

 lengthen the radii vectores, and the 

 earth ascends to its aphelion. On the 

 same principle, cricket-players, for cor- 

 rect play, require truly-formed and ex- 

 actly equipoised cricket-balls, and du- 

 ellists true spherical bullets. The very 

 deflections of motion, which irregular 

 form gives to those bodies, the irregu- 

 lar form of the earth gives to its mo- 

 tions in its orbit. Perhaps, in (he spe- 

 culations of human science on the 

 analogies of the small and the great, 

 a more exact analogy could not be ad- 

 duced in illustraticm of nature, on a 

 subject whose comparative vaslness 

 baflies ordinary illustration. 



Similar orbits in all the planets may 

 be produced by similar means. 



The Moon has, and can have, no 

 fluids; but her primary having them, 

 her orbit is varied by its ^ arious re-ac- 

 tions. 



If it^be objected that this is a vague 

 cause which can never be the subject 

 of symbolical rf-jiresentation, or mathe- 

 matical determination, it may be replied, 

 that residts alone are the objects of our 

 investigations, ruid that these are clear 

 and decided, however intricate or mul- 

 tiplied may be the details of the cause. 

 The rc-action is always equivalent to 



[April 1, 



the Projectile Force, and may be adopt- 

 ed for it in every part of the orbit; 

 while the Solar momentum, conveyed 

 through the medium of space to the 

 planet, is mechanically and mathemati- 

 cally analogous in its eflfect to the at- 

 tractive force. The })hilosophy and 

 the reasoning are different, but the ma- 

 thematical principles and demonstra- 

 tions remain nearly the same. 



It has been urged that the momenta 

 of the sun in circular impulses, would 

 impel or drive oft" the earth and planets 

 in tangents. This is partly false and 

 partly true. It is false if it be hence 

 inferred, that a solar impulse wafted 

 through the medium of space to a pla- 

 netary atmosphere, would drive it into 

 space to any considerable distance. The 

 gaseous medium of space, which is itself 

 the propagator of motion, won Id prevent 

 it ; and it is only by supposing an im- 

 pulse given in a vacuum, thata motion 

 in a tangent could be apprehended, and 

 there is no vacuum. At the same time 

 the position is true in a qualified sense, 

 and the ])henomcna correspond. The 

 planets are urged by the sun into tan- 

 gents. What is a curve but a series of 

 infinitely small tangents? If two con- 

 centric curves wei-e sub-divided by 

 ladii, into any equal number of tan- 

 gents (or in this case impulses) would 

 not the tangents in each be to the 

 other as the radii ? Thus if the sun 

 were supposed to mo're in its orbit, 

 through the infinitely small tangent 

 of an inch, it would move the earth 

 through, perhaps, a million of inches. 

 Is not this a species of tangent ? And 

 so for every inch the sim mo%'es in the 

 successive small chords or tangents of 

 its orbit, would the earth move a mil- 

 lion of inches ; and hence arises the 

 difference in the size and curvature 

 of their orbits. The earth, in like 

 manner, impels the moon in a larger 

 orbit, round their common fulcrum; 

 and, for every inch it moves, it impels 

 the moon in a species of tangent 64 

 inches ; the sum of which spaces of 

 inches, and 64 inches, makes up their 

 mutual orbits. But neither the earth 

 in regard to the sun, nor the moon in 

 iTgard to the earth, are driven to any 

 extra distance, for the impulse commu- 

 nicated by the medium of space, is 

 constantly corrected and resisted by 

 the same medium. 



There is a difficulty about the pro- 

 gression of the Line of Apsides, which 

 it may be worth while to consider. 

 How can the local action of tlie waters 

 produce 



