1,38 Mayow 



ing with greater ease through such bodies as are ex- 

 tremely rigid and crammed with nitro-aerial particles- 

 — glass, for instance, and similar substances, but above 

 all, aerial particles whose rigidity is due to nitro-aerial 

 particles densely infixed in them, as I previously 

 endeavoured to show. 



Here too we can appeal to an experiment re- 

 ferred to by the Hon. Robert Boyle ; to wit, when 

 air is suddenly pumped from a glass vessel, the glass 

 soon becomes dark inside and seems to be filled with 

 nebulous fumes, and besides light, or rather a certain 

 momentary whiteness, is sometimes produced in it. 

 This I think is to be accounted for by the immediate 

 expansion of the residuary particles of air, when the 

 greater part of the air \s pumped from the glass ; not 

 otherwise than as steel springs which have been bent 

 round coil upon coil, open out in a moment as soon 

 as the force by which they were bent is with-^ 

 drawn. But when aerial particles extend themelves in 

 this way, their structure changes at each successive 

 moment in which the movement of recoil takes place,, 

 (as is evident from what has been said on the subject 

 of elasticity) ; whence it is that the rays of light are 

 somewhat interrupted, for, namely, the nitro-aerial 

 particles infixed in the aerial particles, by whose im- 

 pulse moreover light is transmitted, move with a 

 motion different from that by which the action of light 

 is propagated ; so that the aerial particles cannot now 

 transmit the impulse of light as they would otherwise 

 do, but reflect it in the manner of a mirror. But as- 

 soon as the aerial particles cease from their motion of 

 recoil, the glass becomes again pellucid. 



OF COLOURS 

 But with a view to a clearer understanding of the 



