Page:A Voyage in Space (1913).djvu/236

From Wikisource
Jump to navigation Jump to search
This page has been validated.



of the Sun, where we see great red flames shooting up to enormous heights. Perhaps we ought not to call them flames, because in our earthly fire-grates a flame means that something is being burnt, generally the gas from the coal which is being burnt up in the air. The solar flames do not represent anything burning; they glow like the filament of an electric lamp, but we have no better word to describe them than "flames."

We cannot see these flames in the ordinary way; but because they are of a special red colour we can see them by means of a trick. You remember our experiments with colours two lectures ago: we found that a red ribbon would show bright in the red, but in green light it appeared black; and do you remember how we lighted the room with the yellow light made by burning common salt, and then only yellow things showed bright? All other colours in a picture we were looking at—the reds and blues and violets—all disappeared. If we had taken a photograph in this yellow light, the yellow parts of the picture would have shown up, while the others would have been quite faint or altogether absent. And I then told you that this trick was used to take photographs, with an instrument called the spectro-heliograph, and with this instrument we can photograph the red flames round the Sun's edge; of course we use red light in order to show them up. The general plan is simply this: if we pass the Sun's light through a glass prism we have seen that it is spread out into all the different colours. Now let us block out all the other colours except the special red we want; for