Lesson xxv.l LIGHT AND COLOCRS. 157 



on the subject will be agreeable thereto ; though it 

 must be allowed that some rather formidable ob- 

 jections have been advanced against it. 



The Newtonians maintain, that Light consists of 

 a great number of exceedingly small particles, 

 thrown off from the luminous body by a repulsive 

 power with an immense velocity, and in all direc- 

 tions ; hence, Light is produced from motion : but 

 then as all motion will not produce Light, there- 

 fore much manifestly depends on the quality of 

 certain bodies which are of themselves luminous, 

 and have the constant and invariable property of 

 emitting or sending forth these very minute parti- 

 cles : such is the property of the sun, a star, a can- 

 dle alighted, and all sorts of flame, &c. The velo- 

 city of the particles of Light is truly astonishing, 

 amounting to near two hundred thousand miles in 

 a second of time, which is almost a million times 

 greater than the velocity of a cannon-ball. This 

 may be easily proved by observations on the 

 eclipses of Jupiter's satellites ; for when the earth 

 is between the sun and this planet those eclipses 

 will happen about 81 minutes sooner, than accord- 

 ing to the tables ; but when tke earth is in the con- 

 trary position, the eclipses happen about 8J mi- 

 nutes later than they are predicted by the tables. 

 Hence, therefore, light takes up about 8\ minutes 

 in passing from the sun to the earth, a distance of 

 95 millions of miles : whence what was mentioned 

 just above may be deduced. 



Since Light diffuses itself every way with such 

 incredible velocity, it is evident that if its particles 



were 



