EXTRACTS FROM " MICROGRAPHIA." 185 



swifter) as the waves or rings on the surface of the water 

 do swell into bigger and bigger circles about a point of it 

 where, by the sinking of a stone, the motion was begun ; 

 whence it necessarily follows that all the parts of these 

 .spheres undulated through an Homogeneous medium cut 

 the rays in right angles. 



" But because all transparent mediums are not Homo- 

 geneous to one another, therefore we will next examine, 

 how this pulse or motion will be propagated through 

 differingly transparent mediums. And here, according to 

 the most acute and excellent Philosopher Des Cartes, 1 

 suppose the sign of the angle of inclination in the first 

 medium to be the sign of refraction in the second, as the 

 density of the first to the density of the second. By density 

 I mean not the density in respect of gravity (with which 

 the refractions or transparency of mediums hold no pro- 

 portion) but in respect only to the trajection of the Rays of 

 light, in which respect they only differ in this, that the one 

 propagates the pulse more easily and weakly, the other 

 more slowly, but more strongly." 



Extract from " Traite Elementaire de Chimie" Lavoisier, 

 p. 4.. :— 



" On en peut dire autant de tous les corps de la Nature • 

 ils sont ou solides, ou liquides, ou dans l'etat elastique et 

 aeriforme, suivant le rapport qui existe entre la force 

 attractive de leur molecules et la force repulsive de la chaleur, 

 ou, ce qui revient au meme suivant le degre de chaleur 

 auquel ils sont exposes. 



"II est diflficile de concevoir ces phenomenes sans 

 admettre qu'ils sont 1'erTet d'une substance reelle et materielle, 

 d'un fluide tres-subtil qui s'insinue a travers les molecules de 



