

73 



our organs of sight.' The disciples of Plato contrt. 

 buted not a little to the advancement of optics, by 

 the important discovery they made, that light emits it. 

 self in straight lines, and that the angle of incidence 

 is always equal to the angle of reflection. 



2. Plato also seems to have apprehended the New* 

 tonian system of colours : for he calls them the ef- 

 fect of light transmitted from bodies, the small par- 

 ticles of which were adapted to tfye ^rgans of sight. 

 Now is not this precisely the same with what Sir Isaac 

 teaches, " that the different sensations of each par- 

 ticular colour are excited in us by the difference of 

 size in those small particles of light which form the 

 several rays ; those small particles occasioning differ- 

 ent images of colour, as the vibration is more or less 

 lively with which they strike our sense ?" The same 

 philosopher hath gone further : he hath entered into 

 a detail of the composition of colours, and inquired 

 into the visible effects that must arise from a mixture 

 of the different rays of which light itself is .composed. 

 And what he advances a little farther on, that it \vas 

 not in the power of man exactly to determine what the 

 proportion of this mixture should be in certain co- 

 lours, sufficiently shews, that he had an idea of this 

 theory, though he judged it almost impossible to un- 

 fold it ; which makes him add, that should any one 

 arrive at the knowledge of this proportion, he ought 

 not to hazard I he discovery of it, since it would be 

 impossible to demonstrate it by clear and convincing 

 proofs : and yet lie thought certain rules might belaid 

 down respecting trua subject, if in following arid imi. 

 tating nature, we could arrive at the art of forming 

 a diversity ot colours, by the combined intermixture 

 of others,' And he afterwards adds, what may be re- 

 garded as the noblest euiogtum thai ever was made on 

 Si f Isaac Newton; u yea, should ever any one," exclaims 

 tiiat tine genius of antiquity, ' attempt by curious re- 

 searc.i to account for this admirable mechanism, he 

 will, in doing so, but mamiest how entirely ignorant 



TOI*. v. E 



