APPENDIX F: NEWTON 421 



chiefly conversant in the moving of bodies, it comes to pass that 

 geometry is commonly referred to their magnitudes, and mechanics 

 to their motion. In this sense rational mechanics will be the science 

 of motions resulting from any forces whatsoever, and of the forces 

 required to produce any motion, accurately proposed and demon- 

 strated. This part of mechanics was cultivated by the ancients in 

 the five powers which relate to manual arts, who considered gravity 

 (it not being a manual power) no otherwise than as it moved weights 

 by those powers. Our design, not respecting arts, but philosophy, 

 and our subject, not manual, but natural, powers, we consider chiefly 

 those things which relate to gravity, levity, elastic force, the resistance 

 of fluids, and the like forces, whether attractive or impulsive; and 

 therefore we offer this work as mathematical principles of philosophy ; 

 for all the difficulty of philosophy seems to consist in this from the 

 phenomena of motions to investigate the forces of nature, and then 

 from these forces to demonstrate the other phenomena ; and to this 

 end the general propositions in the first and second book are directed. 

 In the third book we give an example of this in the explication of the 

 system of the World ; for by the propositions mathematically demon- 

 strated in the first book, we there derive from the celestial phenomena 

 the forces of gravity with which bodies tend to the sun and the several 

 planets. Then, from these forces, by other propositions which are 

 also mathematical, we deduce the motions of the planets, the comets, 

 the moon, and the sea. I wish we could derive the rest of the phe- 

 nomena of nature by the same kind of reasoning from mechanical 

 principles ; for I am induced by many reasons to suspect that they 

 may all depend upon certain forces by which the particles of bodies, 

 by some causes hitherto unknown, are either mutually impelled 

 towards each other, and cohere in regular figures, or are repelled and 

 recede from each other; which forces being unknown, philosophers 

 have hitherto attempted the search of nature in vain; but I hope 

 the principles here laid down will afford some light either to that or 

 some truer method of philosophy. 



In the publication of this work, the most acute and universally 

 learned Mr. Edmund Halley not only assisted me with his pains in 

 correcting the press and taking care of the schemes, but it was to his 

 solicitations that its becoming public is owing ; for when he had ob- 

 tained of me my demonstrations of the figures of the celestial orbits, 

 he continually pressed me to communicate the same to the Royal 



