Manchester Memoirs, Vol. I. (1906), No. X 15 



volcano, which took years to fall. Many of us remember 

 the beautiful sunset glows of the years near 1884, which 

 were probably due to the existence of this dust high up 

 in our atmosphere, and Professor Stokes showed how the 

 observed rate of fall of these particles was just such as 

 might be inferred from observations of the way in which 

 they scattered light. But if I understand his formula 

 rightly, the rate of fall would be nearly uniform at all 

 heights. It would not at any rate diminish as the particles 

 approach the earth at a rate so marked as the cube of the 

 distance, which is the kind of change we require. We 

 must, of course, be cautious in arguing from our own 

 atmosphere to that of the sun, but in default of positive 

 knowledge to the contrary, I put this supposition aside as 

 not helpful for the illustration of our present problem. 

 [It seems, however, just possible that the resistance of the 

 gaseous atmosphere, combined with a resultant force out- 

 zvards, might satisfy the conditions. This consideration 

 occurred to me too late for full examination.] 



Let us, then, turn to some other supposition. Light 

 pressure or electrical repulsion must not overcome gravity, 

 but they may considerably reduce it. One result of this 

 reduction is that a much smaller velocity is necessary to 

 carry a particle to a given height from the sun. If gravity 

 were not so reduced, a velocity of 382 miles per second 

 would be necessary to eject a particle completely from 

 the sun so that it never returns, and a velocity not much 

 less is required to eject it to heights such as are repre- 

 sented in the corona. For instance, to reach a height of 

 one solar diameter the velocity must be 270 miles per 

 second. There is nothing impossible or even unlikely 

 in the existence of such velocities at the sun's surface 

 a priori, though presently we shall see some reason for 

 doubting their existence. But for the moment let us 



