144 Mayow 



a certain new motion, by which the medium of vision 

 is struck with an impulse distinct from the action of 

 light. For we notice that the rays of light do not, 

 like igneous particles, spread their image in all directions 

 around. For when the rays of light pass through the 

 aforesaid chamber, they are seen only by an eye which 

 directly faces them but not, as we showed above, by 

 an eye situated at the side. Whence we may infer 

 that nitro-aerial particles in a burning body are some- 

 how driven round in a circle, and in their circular 

 motion strike the medium of vision all round, but that 

 the luminous particles move only in straight lines, so 

 that, whether by very frequent blows or by a kind of 

 pressure, they impel the visible medium directly 

 forward only, but not^ to the side. And indeed the 

 action of light tends to move straight forward, pre- 

 cisely as if it were projected in a straight line ; for the 

 rays of light, when they strike upon a plane, are re- 

 flected like a solid body at an angle of reflection equal 

 to the angle of incidence. But when luminous par- 

 ticles impinge on an illuminated body they probably 

 acquire a new tremulous motion and are moved with 

 very short and frequent vibrations, precisely as happens 

 to a dart when it is thrown and one end of it strikes 

 a solid body. Hence it is that the medium of vision is 

 struck by the vibration of luminous particles even on 

 the sides and in all directions. But since this sort of 

 vibration of the luminous corpuscles varies according to 

 the diversity in the surface of the illuminated bodies, and 

 since, in fine, the medium of vision is differently impelled 

 by it, hence it is that the diverse perceptions of colours 

 and of images are produced and propagated all round. 

 With respect to the glittering white colour which 

 a brightly shining lamp shows, it seems to depend on 

 this, that the particles of the shining body, agitated 



