2 Marvels of the Universe 



As the " flames " were only seen during eclipses, when the moon was exactly before the sun, 

 it was disputed for some time to which of these bodies they belonged — an important question for 

 decision ; for, as the sun is four hundred times more distant than the moon, the prominences, if 

 solar, must be on four hundred times the scale that they would be if lunar. The eclipses of 1842 and 

 1 85 1 proved that they were really parts of the sun, but not solid parts ; for one prominence was 

 bent over like a boomerang, and another floated free like a cloud. It was evident, therefore, that 

 they were something of the nature of vapour, gas, or flame. 



In t'ue eclipse of 1868 the spectroscope was brought to bear upon these objects, and revealed 

 that they consisted of intensely heated gases — " flames," therefore, in no mere metaphorical sense — 

 hydrogen being the first gas to be recognized in them. 



But the spectroscope enabled the prominences to be seen without an eclipse. The hindrance 

 to their being seen in ordinary daylight lies in the overpowering glare from the sky in the immediate 

 neighbourhood of the sun ; but with a spectroscope of high dispersion this glare can be greath' 

 weakened without much reducing the brightness of the prominence, as it is seen in one or other 

 of the four bright lines of the spectrum of hydrogen. When the slit of the spectroscope can be 



These are two views of the same solar eruption, the second one being taken twenty-five minutes after the first. 



opened comparatively wide, the observer looks out through it, as it were, to see the flames which 

 appear on the spectrum somewhat as shown in the diagram. 



A quarter of a century later an ingenious arrangement was devised bv several astronomers 

 independently, amongst them by Professor Hale, then Director of the Kenwood Observatory, U.S..-V., 

 by which one of the bright prominence lines could be isolated from the rest of the spectrum, and a 

 photograph in its light could be taken of the entire surface of the sun, together with its immediate 

 surroundings. The wonderful achievements of this new instrument, the " Spectroheliograph," 

 will form the subject of a later paper. Two of Professor Hale's earliest prominence photographs 

 are, however, reproduced here. 



\\'hen the spectroscopic method of observing the " flames " was established in 1868, it was seen, 

 on e-xamining the circumference of the sun, that it is everywhere surrounded by a layer of bright 

 hydrogen, some five thousand miles in depth, the upper surface of which is notched hke a saw, and 

 hence is sometimes called the " sierra," but more generally the " chromosphere." It suggests the 

 turbulent surface of a sea of flames, from whose jagged flickering points there rise irregularly jets 

 and streamers of the same material in the most fantastic forms and of every variety of size. Some- 

 times they resemble groves of trees, or quiet hedgerows ; sometimes the delicate lace-work of cirrus, 

 or the rounded masses of cumulus clouds ; sometimes thev are jets of fire, rushing forth under 

 tremendous pressure, or torn and driven as by some terrible explosion. Thus they readily fall 

 into two great classes — the quiet and eruptive proininences. 



The quiet prominences are chiefly composed of hydrogen, and change their shape slowly. They 



