10 Life and Letters of Francis Galton
representation of these appearances, in the case of small black snow-laden clouds sailing before the sun. When the clouds are in any way transparent, though some indications of these brushes
may be observed, their effect is proportionately feeble, and if the sun be masked by an object at no great distance, the effect does not occur at all. The common artist representations of the sun about to rise over a distant hill, show that these appearances are generally recognised. Now I can hardly understand what I have described, on•any other supposition than that of sun-beams being reflected from off the back of the cloud at a very acute angle athwart the line of sight. They would illuminate the haze of the atmosphere through which they passed, and being seen exceedingly foreshortened, would be the more apparent. But here I stop. I do not comprehend why the wisps of light should be projected from the cusps of the uncovering sun, and therefore have an apparent movement of revolution. Still less can I understand why the moon, which is presumed to have no atmosphere of any description', capable of being illumined by passing rays, should exhibit this appearance so beautifully. When I shall have seen wisps of light, as in Figs. 3 or 4, coming from a cloud, but shaped in any way like those of Fig. 1-convergent and not divergent, curved and not straight-whether owing to irregular distribution of the adjacent haze or other intelligible reason, I shall hardly resist feeling satisfied that the Corona is mainly due to the same description of cause that produces them, whatever that cause may really be. There may, in addition, be some luminous effect produced by an enveloping atmosphere of light round the sun, seen beyond the edges of the eclipsing moon
As to my colours : after a good deal of trouble, I find I can reproduce the exact effect that I witnessed, by placing them in a closed box having a dark ceiling, and admitting a faint white light at a low angle. I then view the colours also at a low angle through a piece of dull yellow glass. All these details seem essential to effect: they are in some sort, the equivalents to a yellow sky near the horizon, and gloom above head." (V.T. 1860, pp. 440-4.)
We have given this long extract from Galton's paper because it shows not only the working of Galton's mind at the time, but is very characteristic of the general manner in which he approached problems. He thought and reasoned about things for himself even when they might lead him astray. His curved corona rays have been confirmed. He alone noted that cusp rays were still visible when the crescent was masked by the hand. Galton's observations (but not his inferences from them) will be found in Ranyard's "Observations made during Total Solar Eclipses" (Memoirs of R. Astron. Soc. Vol. XLT, 1879), where his sketches are reproduced (pp. 563-4) in more finished form.
' The brushes according to Galton's sketch extended to three times the moon's diameter.