ATOMS AND SUNBEAMS. 131 



gaseous in tlieir character, or, at all events, come sufrtciently near to 

 matter in tlie gaseous state to i)ermit the api)lication of tlie line of 

 argument with which we have hitherto been engaged. In consequence 

 of the vast mass of the sun the gravitation with which it draws all 

 bodies towards it is very much greater than the gravitation on the 

 surface of the earth. On our globe we know that the effetit of gravita- 

 tion is to impart to any body near the surface velocity directed towards 

 the earth's center at the rate of 32 feet per second. The sun is more 

 than three hundred thousand times as massive as the earth; we can 

 not however assert that the gravitation is increased in the same pro- 

 portion, because, on account of the vast size of the sun, a particle at 

 its surface is more than a hundred times farther away from tlie solar 

 center than a body on the surface of the earth is from the terrestrial 

 center. It can however be shown, that taking these various matters 

 into account, the actual intensity of gravitation at the solar surface is 

 sufficient to tend to impart to all objects an increase of velocity towards 

 the sun's center at the rate of 457 feet per second. This would apply 

 not only to a meteorite, or other considerable mass, which is falling 

 into the sun; it would be equally true of an object as small as a mole- 

 cule. Every one of the myriads of gaseous molecules in the outer 

 regions of the solar atmosphere must be constantly acted upon by this 

 attractive force, which tends in the course of each second to add to 

 them a downward velocity at that rate per second which has already 

 been stated. It is quite true that to a great extent the effect of this 

 attraction is masked by counteracting tendencies. In particular we 

 may mention that inasmuch as the density of the solar atmosphere 

 increases as the sun's center is ajiproached, the Hying molecule gener- 

 erally fiuds itself more obstructed by encounters with other molecules 

 when it is descending than whenic is ascending. 



We may here contrast the condition of the atmosphere on the earth 

 with the condition of the solar atmosphere. Each molecule in our air, 

 being acted upon by terrestrial gravitation, has thereby a tendency to 

 fall downward with a velocity continually increasing at the rate of 32 

 feet per second. As however the terrestrial atmosphere has long since 

 reached a stable condition, in which it undergoes no further contrac- 

 tion, the effect of gravitation in adding velocity to the molecules is so 

 completely masked by the counteracting tendencies, that on the whole, 

 there is no continual increase of molecular velocities downward due to 

 gravitation. Were such an increase at present going on, we should 

 necessarily find that the terrestrial atmosphere was decreasing in vol- 

 ume, and ever becoming more condensed in its lower strata. It is 

 however well known that no such changes as are here implied are 

 taking place. The essential difference between the earth and the sun, 

 (so far as the matter now before us is concerned,) is to be found in the 

 fact that as the sun has not yet passed into the form of a rigid body, 

 it is still contracting at a rate very much gi eater than that at which a 



