250 DISCOURSE ON THE STUDY 



produce an impression of the objects. Vague and 

 clumsy as this hypothesis obviously is, it assigns to 

 the object a power, and to light a diffusive propa- 

 gation in all directions, which are, the one and the 

 other, independent of our eyes, and therefore goes 

 to separate the phenomena of light from those of 

 vision. 



(274.) The hypothesis of Newton is a refinement 

 and improvement on this idea. Instead of spectra or 

 resemblances, he supposes luminous objects actually 

 to dart out from them in all directions, particles, of 

 inconceivable minuteness (as indeed they must be, 

 having such an enormous velocity (see 17.), not to 

 dash in pieces every thing they strike upon). These 

 particles he supposes to be acted upon by attractive 

 and repulsive forces, residing in all material bodies, 

 the latter extending to some very small distance 

 beyond their surfaces ; and by the action of these 

 forces to be turned aside from their natural straight- 

 lined course, without ever coming in actual contact 

 with the particles themselves of the bodies on which 

 they fall, but either being turned back and reflected 

 by the repulsive forces before they reach them, or 

 penetrating between their intervals, as a bird may 

 be supposed to fly through the branches of a forest, 

 and undergoing all their actions, to take at quitting 

 them a direction finally determined by the position 

 of the surface at which they emerge with respect 

 to their course. 



(275.) This hypothesis, which was discussed and 

 reasoned upon by Newton in a manner worthy of 

 himself, affords, by the application of the same 

 dynamical laws which he had applied with so much 







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