372 CELESTIAL CHEMISTRY. 



calcium vapour, so vast, and so overheated that they more than 

 compensate for the absorption of hght caused by the cooler 

 metallic vapours, and in the middle of what we may call the dark 

 shadow line of calcium, the bright calcium line reappears. If 

 we call the black line across the spectrum a reversal of the 

 light, we may call this a double reversal, and so we become 

 aware of the fact that some of the prominences consist largely 

 of intensely glowing calcium vapour. Some idea of the 

 appearance of these huge tongues of flame may be gathered 

 from observations made in 1870 by Respighi. They flicker to 

 and fro apparently with as great ease as the flames that arise 

 from a burning block of buildings, but the incomprehensible 

 velocity of those flaming tongues of hydrogen may be faintly 

 gathered from two drawings of a solar storm made by Sir 

 Xorman Lockyer on the 14th March, 1869. The flames on this 

 occasion were nearly 30.000 miles high, and how swiftly they 

 moved is implied in the fact that they changed from a nearly 

 vertical position to almost a semicircle in the short space of ten 

 minutes. In June. 189 1 Professor Fenyi observed a mass of 

 flame shoot vertically upwards to a height of over 100,000 miles 

 with a velocity of 18,000 miles per second. These are of course 

 velocities across the line of vision. By the displacement of the 

 Fraunhofer lines to right or left we ar,e furnished with a means 

 of gauging velocities along the line of sight and from these 

 two components actual velocities may be calculated, but into 

 that phase I cannot enter now. 



Vaster in extent even than the chromosphere with its 

 protuberances, is the solar corona. Its appearance is that of a 

 halo of greenish or pearly light stretching away into space on 

 either side from the sun's denser body. So faintly luminous 

 is this corona that even during eclipses there have been but 

 few opportunities of examining in at length. It stretches, how- 

 ever, over a distance, from extremity to extremity of about six 

 times the sun's diameter, that is to say, nearly 5,000,000 miles 

 in all. Even the spectroscope has told' us very little about the 

 corona; it gives a bright line spectrum, which occasionally 

 shows hydrogen, but also exhibits a green line not given by any 

 known element. This is obviously a repetition of Sir Xorman 

 Lockver's experience with regard to helium, and to this new 

 element in the sun's corona the name coronium has been 

 assigned. Before helium had been discovered on earth it had 

 been predicted that both helium as well as coronium. to judge 

 from their positions in the sun's atmosphere, would, when 

 found, probably prove to approximate in lightness to hydrogen, 

 the lightest substance hitherto known. It was, in fact suggested 

 that they would perhaps be found far lighter even than 

 hvdrogen. To a certain extent this prediction was verilied when 

 Sir William Ramsay discovered helium on earth. It turns out 

 to be — not indeed lighter than hydrogen — but next to hydrogen 

 it is now the lightest gas known. As for coronium, it has not 

 yet come within handling distance, but it is not at all 

 improbable that wdien we find it, and are able to estimate its 

 weight, it will prove to be even lighter and more subtle than 

 -either helium or hvdrogen. 



