TWO YEARS LATER. 31 



yet we cannot see the prominences. Sir George 

 Airy tried the experiment long since. He placed a 

 card, out of which a circular aperture had been cut, in 

 such a way that the image of the sun, formed by a 

 powerful telescope, would have been visible in the 

 place whence the card-circle had been removed the 

 image just filling that space. Under the actual 

 arrangement, however, the light passed through the 

 aperture, and was received into a black bag, where it 

 was quenched. Now, it might have been supposed 

 thatr by this ingenious method the image of the 

 prominences would have been rendered visible all 

 round the circular aperture. But the glare from the 

 illuminated air was much more than sufficient to 

 obliterate all traces of them. And so it might seem 

 that no means we could adopt would render the 

 prominences visible. But it occurred to Janssen that 

 since the spectroscope turns the solar light into a long 

 streak which can be made as dim as we please by 

 increasing its length while the same instrument 

 turns the prominence-light into a few bright lines 

 which are unchangeable in brightness it might be 

 possible to see these lines after sufficiently reducing 

 the light of the rainbow-tinted solar streak. He tried 

 this the day after the eclipse, and found that it was 

 so : he could distinctly see the prominences-lines even 

 when the sun was shining with full splendour. 



Janssen sent news of this discovery to Europe, and 

 on a certain day, nearly two months after the eclipse, 

 the letter announcing the discovery was placed in the 



