EXTRACTS FROM " MICROGRAPHIA." 1 83 



must after many rubbings decay and be wasted ; but we 

 have no reason to suspect the latter, especially if we 

 consider the exceeding difficulty that is found in cutting 

 or wearing away a Diamond. And a circular motion of 

 the parts is much more improbable, since, if that were 

 granted, and they be suppos'd irregular and angular parts, 

 I see not how the parts of the Diamond should hold so 

 firmly together, or remain in the same sensible dimensions 

 which yet they do. 



" Next, if they be Globular, and mov'd only with a 

 turbinated motion, I know not any cause that can impress 

 that motion upon the pellucid medium, which yet is done. 

 Thirdly, any other irregidar motion of the parts one 

 amongst another, must necessarily make the body of a 

 fluid consistence, from which it is far enough. It must 

 therefore be a vibrating motion. 



"And thirdly, that it is a very short vibrating motion, 

 I think the instances drawn from the shining of Diamonds 

 will also make probable. For a Diamond being the hardest 

 body we yet know in the world, and consequently the 

 least apt to yield or bend, must consequently also have its 

 vibrations exceeding short, and these, I think, are the three 

 principal proprieties of a motion requisite to produce the 

 effect called light in the object. 



" The next thing we are to consider is the way or 

 manner of the trajection of this motion through the inter- 

 pos'd pellucid body to the eye. And here it will be easily 

 granted, 



" First, That it must be a body susceptible and impartible 

 of this motion that will deserve the name of a Transparent. 

 And next, that the parts of such a body must be Homo- 

 geneous, or of the same kind. Thirdly, that the constitution 



