id PHILOSOPHICAL TRANSACTIONS i [aNNO I672. 



the corporeity of light; but I do it without any absolute positiveness, as the 

 word perhaps intimates; and make it at most but a very plausible consequence 

 of the doctrine, and not a fundamental supposition, nor so much as any part of 

 it; which was wholly comprehended in the precedent propositions, ^nd I some- 

 what wonder how the objector could imagine, that when I had asserted the 

 theory with the greatest rigour, I should be so forgetful as afterwards to assert 

 the fundamental supposition itself with no more than a perhaps. Had I intended 

 any such hypothesis I should somewhere have explained it. But I knew that 

 the properties which I declared of light, were in some measure capable of being 

 explicated, not only by that, but by many other mechanical hypotheses. And 

 therefore I chose to decline them 'all, and to speak of light in general terms, 

 considering it abstractly, as something or other propagated every way in straight 

 lines from luminous bodies, without determining what that thing is; whether a 

 confused mixture of difForm qualities, or modes of bodies, or of bodies them- 

 selves, or of any virtues, powers, or beings whatsoever. And for the same rea- 

 son I chose to speak of colours according to the information of our senses, as if 

 they were qualities of light without us. Whereas by that hypothesis I must 

 have considered them rather as modes of sensation, excited in the mind by 

 various motions, figures, or sizes of the corpuscles of light, making various me- 

 chanical impressions on the organ of sense; as I expressed it in that place, 

 where I spake of the corporeity of light. 



But supposing I had propounded that hypothesis, I understand not, why the 

 objector should so much endeavour to oppose it. For certainly it has a much 

 greater affinity with his own hypothesis, than he seems to be aware of; the 

 vibrations of the asther being as useful and necessary in this as in his. For assum- 

 ing the rays of light to be small bodies, emitted every way from shining sub- 

 stances, those', when they impinge on any refracting or reflecting superficies, 

 must as necessarily excite vibrations in the asther, as stones do in water when 

 thrown into it. And supposing these vibrations to be of several depths or 

 thicknesses, accordingly as they are excited by the said corpuscular rays of 

 various sizes and velocities; of what use they will be for explicating the manner 

 of reflection and refraction, the production of heat by the sun beams, the 

 emission of light from burning, putrifying, or other substances whose parts are 

 vehemently agitated, the phaenomena of thin transparent plates and bubbles, and 

 of all natural bodies, the manner of vision, and the difference of colours, as 

 also their harmony and discord; I shall leave to their consideration, who may 

 think it worth their endeavour to apply this hypothesis to the solution of phae- 

 nomena. 



In the second place, I told you that the objector's hypothesis, as to the funda- 



