OF COMMON MATTER. 157 



are endowed, it must, nevertheless, be admit- 

 ted, that the velocity with which it moves, and 

 the extreme subtilty and exility of which its 

 particles are constituted, are equally deserving 

 our admiration and astonishment. Although 

 these attributes, from the very nature of them, 

 might be expected to evade the researches of the 

 most learned : the attentive observation of the 

 ingenious have, nevertheless, in some measure, 

 succeeded in ascertaining the degrees of the 

 one, as well as of the other. Among the most 

 illustrious of these, may be mentioned Dr. 

 BRADLEY, REAUMUR, and CASSINI ; the data 

 on which they proceeded, with respect to the 

 motion of light, were founded on the eclipses, 

 which the satellites or moons of the planet 

 Jupiter, undergo. By observation, they found 

 that the eclipses of these satellites appeared, in 

 fact, sooner than they ought, by hypothesis, to do, 

 when Jupiter was nearer to the earth ; and later, 

 When that planet was on the farthest side of her 

 orbit; or, in other words, that the time when 

 these eclipses appeared, was always influenced 

 by the degree of distance. By observations, such 

 as these, they were enabled to show, that 

 although the motion of the solar rays, is not 

 instantaneous, but progressive it, nevertheless, 

 flows with the astonishing velocity of 200,000 

 miles in every second of time; so that, admit- 

 ting the sun to be 95,513,794 English miles 



