EXPERIMENT ON VELOCITY. 243 



jeet to universal attraction ; it would with difficulty be 

 darted out from an incandescent body, because the attrac- 

 tion of that body will tend to carry it back again ; hence 

 a gradual diminution of its original velocity must un- 

 doubtedly take place ; it is only necessaiy to inquire 

 whether observation can enable us to discover it. It 

 would be a simple question of calculation how, in mak- 

 ing some suppositions with respect, to the physical con- 

 stitution of certain fixed stars in respect to their size and 

 density, which do not appear extravagant, we find that 

 they may, by their attractive force, annihilate altogether 

 the velocity of emission of luminous molecules ; that 

 after having j^roceeded to a given distance, these mole- 

 cules, which had so far separated themselves from the 

 body, must return thither by a retrograde movement. 

 Thus, certain stars might be as luminous as the sun, to 

 the distance of 40,000,000 leagues, for example, and 

 beyond that be altogether dark ; that distance being the 

 exact limit beyond which none of their rays could pass. 

 If we change considerably the volumes and densities 

 which give these results ; if we assume for stars of the 

 first magnitude such dimensions as no astronomer would 

 refuse to consider as probable, they will no longer pre- 

 sent such strange phenomena, they will no longer be 

 dazzling at this distance, and completely dark at a little 

 farther distance ; but the velocity of their light will 

 change with the distance ; and if two such stars are at 

 very difierent distances from the earth, their rays will 

 arrive at our eyes with dissimilar velocities. Is it not 

 then a formidable objection against the theory of emis- 

 sion, that there should be this perfect equality of velocity 

 in all cases, which all observations testify ? 



There exist very simple means for altering to a nota- 



