l^Q THEORY OF EMISSION DIFFICULTIES. 



of the sun, botli expressed in feet. If wc put v = 192,700 miles, (reduced to 

 feet,) and make m indeterminate, we shall find that the mass must be increased 

 860,000,000,000 fold to be capable of creating, and therefore of destroying, a 

 velocity equal to that of light. This sujiposes the bulk of the sun to be un- 

 altered. But if iilie mass is increased without altering the density we shall 

 have — 



V2mgra 



in which x is the radius of the sun under its supposed enlargement; whence — 



_ vR!^ 

 rv 'ling 



Replacing the symbols by their values, we find that the sun nuist be enlarged 

 to nearly five liundred times his p'csent diameter in order to possess tiie power 

 of entirely arresting the progress of light, considered as material, at any distance. 

 The surface of such a sun would extend more than seventy millions of miles 

 beyond the orbit of Mars. That there may be bodies in the universe so large 

 as this is possible, but we may esteem it hardly probable. If there are, and if 

 light is material, they may be invisible to us. 



A final objection to the material theory of light is found in the phenomena of 

 refraction and reflection. This, though it seems to have been overlooked, is 

 really the most serious of all. Wc have seen that the eftect of the immense 

 power of solar gravitalsou is insufficient to produce more than an inappreciable 

 variation in the velocity of light, during the nearly eight minutes and a quarter 

 which is occupied in its passage over the space between us and the sun; and 

 yet, ii' the hypothesis we are considering be true, there is a force residing in tlie 

 superficial stratum of transparent bodies — a stratum so thin that no attempt has 

 ever been made, or can be made, to measure it— which is capable of instantane- 

 ously doubling and, in some instances, almost tripling this velocity. Thus 

 light which has passed the surface of glass of antimony or chromate of lead 

 must, if this theory is true, have its velocity raised, in the instant of passing, 

 from 192,700 miles to 674,000 miles per second. In common glass the velocity 

 becomes 289,000 rhiles. In ordinary reflection, also, the reflecting force has 

 first to destroy the original velocity, and then to impart an equal velocity in 

 the opposite direction. This is more easily conceivable than the acceleration 

 produced by refraction, as it corresponds with the ordinary phenomena of elas- 

 ticity. But refraction, on the theory we are considering, is only explicable om 

 the hypothesis of attraction ; and the immensity of an attracting force which is 

 capable of accomplishing in so short a time what graxaty is totally unequal to 

 in a time greater beyond measure, is totally inconceivable. 



But, if objections of this weighty description to the material theory of light 

 did not exist, the impossibility of finding in it any satisfactory explanation of 

 the remarkable phenomena which have presented themselves in the later pro- 

 gi'ess of optical discovery, would be conclusive against it ; while the opposing 

 theory finds in these very phenomena its strongest recommendation to accept- 

 ance. It is to that theory, therefore, that attention will be confined in the fol- 

 lowing attempt to connect the fiicts which have been detailed with their proba- 

 ble causes. To repeat the imperfect explanations which have been founded on 

 a hypothesis which is now generally abandoned, would be an luiprofitable waste 

 of time and space. 



