CHROMOSPHERE AND SOLAR PROMINENCES. 389 



the sun rose unobscured, and, as soon as he had completed the neces- 

 sary adjustments, and directed his instrument to the portion of the 

 sun's limb where the day before the most brilliant prominence ap- 

 peared, the same lines came out again, clear and bright ; and now, 

 of course, there was no difficulty in determining at leisure, and with 

 almost absolute accuracy, their position in the spectrum. He immedi- 

 ately confirmed his first conclusion, that hydrogen is the most con- 

 spicuous component of the prominences, but found that the yellow line 

 must be referred to some different element than sodium, being some- 

 what more refrangible then the D lines. 



He found also that, by slightly moving his telescope and causing 

 the image of the sun's limb to take different positions with reference 

 to the slit of his spectroscope, he could even trace out the form and 

 measure the dimensions of the prominences ; and he remained at his 

 station for several days, engaged in these novel and exceedingly 

 interesting observations. 



Of course, he immediately sent home a report of his eclipse-work, 

 and of his new discovery, but, as his station at Guntoor, in Eastern 

 India, was farther from mail communication with Europe than those 

 upon the western coast of the peninsula, his letter did not reach 

 France until some week or two after the accounts of the other ob- 

 servers; when it did arrive, it came to Paris, in company with a 

 communication from Mr. Lockyer, announcing the same discovery, 

 made independently, and even more creditably, since with Mr. Lock- 

 yer it was not suggested by any thing he had seen, but was thought 

 out from fundamental principles. 



Nearly two years previously the idea had occurred to him (and, in- 

 deed, to others also, though he was the first to publish it), that if the 

 protuberances are gaseous, so as to give a spectrum of bright lines, 

 those lines ought to be visible in a spectroscope of sufficient power, 

 even in broad daylight. The principle is simply this : 



Under ordinary circumstances the protuberances are invisible, for 

 the same reason as the stars, in the daytime : they are hidden by the 

 intense light reflected from the particles of our own atmosphere near 

 the sun's place in the sky, and, if we could only sufficiently weaken 

 this atrial illumination, without at the same time weakening their light, 

 the end would be gained. And the spectroscope accomplishes precisely 

 this very thing. Since the air-light is reflected sunshine, it of course pre- 

 sents the same spectrum as sunlight, a continuous band of color crossed 

 by dark lines. Now, this sort of spectrum is greatly weakened by 

 every increase of dispersive power, because the light is spread out into 

 a longer ribbon and made to cover a more extended area. On the 

 other hand, a spectrum of bright lines undergoes no such weakening 

 by an increase in the dispersive power of the spectroscope. The 

 bright lines are only more widely separated — not in the least diffused 

 or shorn of their brightness. If, then, the image of the sun, formed by 



