On the Elliptical Motions of the Planets. 



182].] 



In truth, a common force located in 

 one part of space coukl not produce a 

 regular ineqnaiiiy in the distances of 

 many planets, uor even in any one ; 

 nor could it produce diilereut direclions 

 of the lines of Apsides iu eacli. The 

 supposition is to the last degree absurd, 

 and is a proof that facts are required 

 by Philosophers to yield to their sys- 

 tems. 



Yet it is true that the planets do re- 

 volve in elliptical orbits, that the sun 

 is in one of tlie foci of each, that they 

 do describe equal areas iu equal times, 

 and that there is such a balance of the 

 operating forces as readers the sluipe of 

 tlic orbit dependant ou those forces. 



All this is true, yet the vulgar theory 

 about the Sun's attraction, the plane- 

 tary projectile force, the vacuum iu 

 space, and the suu"s necessary position 

 in one of the foci of an ellipse, is not 

 true, aud has no i-ealiEy but in tiic fer- 

 tility of man's imagination. 



On the contrary it may be laid down 

 as an universal proposition, that every 

 uniform irregularity of single bodies 

 moved with a system of bodies by a 

 common central force, or moved iu 

 any manner by common impulse or 

 percussion, must arise within each body 

 cither from its different density, form or 

 structure, or from variations among its 

 own parts. 



Thus the ceatral wheel, or power in 

 any machinery, may produce various 

 effects at the termination of its motions, 

 as spinning, winding, &c. &c, yet all 

 these variations are produced by the 

 variable structure of the subordinate 

 wheels ; and these produce a variable 

 local result, only in consequence of 

 such local variation iu t!ie construction 

 of the parts. It would be puerile to 

 refer the variable results, to different 

 ju'opcrties of tlie central wheel iuregaid 

 to each, oi- to its owu peculiar relations 

 to each. Nothiijg,ou theothcrhand,can 

 be moi'e ceriain than that each valuation 

 in tha results is an effect of variation 

 in the proximate parts, tiiougli the 

 common origin of force is nevertiieless 

 in the central wheel. 



Wliat then is the particular arrange- 

 ment in each planet wliich forces it to 

 perform a regular elliptical orbit, and 

 have a regular progressive motion of 

 the line of Apsides ? 



It IS agreed on all hands, that a sys- 

 U:\n of action and re-action pervades 

 all the i^odies in the universe. Whe- 

 ther tiio moving powers be Attraction, 

 or whcliier it lie iMotion transferred 

 from body to body, the law of (sjual 



211 



action and re-action is universally and 

 justly admitted. By the old school 

 bodies are said mutually to attract one 

 another in proportion to their quanti- 

 ties of matter, and inversely as the 

 squares of tlieir distances : aud by the 

 new one they are considered as moving 

 one another thri)Ugh the gaseous me- 

 dium of space, by the very same laws. 



It is obvious, therefore, that as the 

 equal action of the sun produces in the 

 planets, orbits, whose parts vary their 

 distance, that the difference or varia- 

 tion is to be found or must exist in the 

 re-actions of the bodies which are 

 patients of such eqxial actions ; for if 

 the re-actions are different, the effect 

 of the motions in intensity and tlirection 

 will proportionally vary. In the varied 

 re-actions, tlien, of the several planets 

 are to be found the tnie mecliauical 

 cause of their elliptical orbits. For the 

 relative lengths of levers, or the sizes or 

 radii of orbits, are inversely as the re- 

 actions of the bodies concerned. 



Nor does it signify whether the proxi- 

 mate cause of this varied re-action be, or 

 be not, determined — for if unknown, it 

 would, iu a mechanical and philosopbi- 

 cal sense, be to be preferred toNewton's 

 Projectile Force; while, independent 

 of the whimsicality, and undetermined 

 direction of such force, the action and 

 re-action, confer on the sun and on the 

 planets, much the same projectile force, 

 each having, in degree, a simultaneous 

 tendency to go oft' in a tangent. 



But in truth there seems little diffi- 

 cultj'' in determining the variable force 

 which converts circular info elliptical 

 orbits. It might be difficult, if, while 

 the same phenomena existed, we 

 found a planet consisting entirely 

 of homogeneous solid matter. All 

 its re-actions would then be uniform 

 if acted upon by an imiform force, and 

 a circular orbit would be the necessary 

 result. The ear.Mi, one of the planets, 

 and that from which we must reason 

 in regard to the rest, is ou the contrary 

 knovvu to be neither tixed nor homoge- 

 neous. It consists for the greater part, 

 at Ipast on its operative circumference, 

 of moving and moveable fluids. These 

 with reference to the fixed parts have, 

 as fluids, the power of accommodating 

 themselves to external forces, by flow- 

 ing towards any side unequally acted 

 upon, and in this varied centrifugal 

 power exists an unequal means and 

 cause of re-action iu the planets. 



But if these moveable fluids were 



equally distributed through or on a 



planet, still the varied re-actions would 



balance 



