1 87 1.] The Fuel of the Sun. 445 



My present business, however, is to show how these 

 vortices and eruptions — this down-rush in one part of the 

 solar atmosphere and up-rush in another — contribute to the 

 permanent maintenance of the solar light and heat. It 

 must be understood that these outbursts are only visible to 

 us as luminous prominences during the period of their ex- 

 plosive outburst, and while still subject to great expansive 

 tension. Long after they have ceased to be visible to us 

 their expansion must continue, until they finally and fully 

 mingle with the medium into which they are flung, and 

 attain a corresponding degree of rarefaction. This must 

 occur at thousands or tens of thousands of miles above the 

 photosphere, according to the magnitude of the ejection. 

 The spectroscopic researches of Frankland and Lockyer 

 have shown that the atmospheric pressure at about the 

 outer surface of the photosphere does not exceed that of our 

 atmosphere, and as we consider that at 100 miles above this 

 we reach the ethereal regions, I may safely regard all the 

 upper portion of these solar ejections as having left the 

 solar atmosphere proper, and become commingled with the 

 general interstellar medium. 



If the sun were stationary, or merely rotating, in the 

 midst of this universal atmosphere, the same material that 

 is ejected to-day would in the course of time return, and be 

 whirled into the great sun-spot eddies ; but such is not the 

 case ; the sun is driving through the ether with a velocity of 

 about 450,000 miles per twenty-four hours. 



What must be the consequence of this motion ? The sun 

 will carry its own special atmospheric matter with it; but it 

 cannot thus carry the whole of the interstellar medium. 

 There must be a limit, graduated no doubt, but still a 

 practical limit, at which its own atmosphere will leave 

 behind, or pass through, the general atmospheric matter. 

 There must be a heaping or condensation of this matter 

 in the front, a rarefaction or wake in the rear, and a 

 continuous flow of newly encountered atmosphere around 

 the boundaries in the opposite direction to that of the 

 sun's motion. The result of this must be that a great 

 portion of the ejected atmospheric matter of the prominences 

 will be swept permanently to the rear, and its place supplied 

 by the material occupying the space into which the sun is 

 advancing. We are thus presented with a mighty ma- 

 chinery of solar respiration ; some of this newly arriving 

 atmospheric matter must be stirred into the vortices, its 

 quantity being exactly equivalent to that of the old material 

 expired by the explosive eruptions, and left in the rear. 



