‘ftances drawn from the fhining of Diamonds will alfomake probable. 
- And here it will be eafily granted, 
MrcROGRAPHIA., 
not return,the Diamorid muft aftermany rubbings decay and be :wafted: 
but we have no reafon to. fufped the latter, efpecially: if wei confider 
amond, a Circular motion’ of the partsiistinuch more:imptobable, 
fince, if that were granted,and they be fetes’ d irregular and Angular 
parts, I fee not how. the parts of the Diamond fhould hold fo firmly to- 
gether, or remain in the fame fenfible dimenfions; which yet. they do, 
Next, if they be Globular, and mov'd only with:a turbznated motion, I 
know not.any caufe that can imprefs that motion upon the pelucid me- 
dium, which yet is done. Thirdly, any other: zrregular motion of the 
parts one.amongft another, muft neceflarily make the body of aa fluid 
confiftence, from which it is far enough. It muft therefore bea Vibra- 
dingmotion. 9) Ly 
And Thirdly, That it is a very hort vibrating motion, Ethink the in- 
For a Diamond being the hardeft body we yet know in the World, and 
confequently the Teal apt to yield or bend, muft confequently alfo have 
its vibrations exceeding fhort. = 
And thefe, I think, are the three principal proprieties of a motion, re- 
quifite to produce the effet call'd Light intheObjeQ. h 
The next thing we are toconfider, is the way or manner of the fraje- 
dion of this motion through the interpos’d pellucid body to the eye: 
Firft, That it muft be a body /afceptible and impartible of this motion 
that will deferve the name of a Tranfparent. And next, that the partsof — 
fuch a body muft be Homogexeous, or of the fame kind. Thirdly, that the 
conftitution and motion of the parts muft be fuch, that the appulfe of the 
luminous body may be communicated or propagated through it to the 
greateft imaginable diftance in the leaft imaginable time; though I fee — 
no reafon to affirm, that it muftbein an inftant : For I know not any one 
Experiment or obfervation that does proveit. And, whereasit may be — 
rizontal Eclypfes that may feem very much to favour this fuppofition of — 
the flower progreffion of Light then moft imagine. And the like may — 
be faid of the Eclypfes of the Sun, &c. But of this only by the by- — 
Fourthly, That the motion is propagated every way through anHomo- — 
geneous 
