Moonlight and Colour. 131 



thrown upon its surface, and if the experiment is made by 

 holding a small piece of coloured glass in the hand, leaving 

 white light to fall upon adjacent portions of the paper, the 

 contrast between the two parts is very distinct. Do the same 

 thing in diffused moonlight, and so little colour is obtained that 

 the chief contrast is that of light and shadow, not of white light 

 and colour, and great surprise is usually felt the first time the 

 operation is performed. 



Unless the piece of coloured glass in the last experiment 

 is held very near the paper, its power of imparting colour to 

 the moonlight is scarcely noticeable, and for anything ap- 

 proaching to the effect described by Keats and Scott, or 

 depicted by Millais, a much brighter moonlight would be 

 required than ordinary mortals ever had the chance to see ; un- 

 less all diffused white light were excluded, so that a general 

 darkness contrasted with limited patches of coloured light. 



When the solar spectrum is viewed by means of a prism, 

 the eye instantly detects a great diversity in brightness as well 

 as in colour ; the yellow and green portions being very brilliant, 

 and the purple deepening into shade. With a spectroscope 

 admitting the light by means of a slit that can be opened or 

 shut at pleasure, it is easy to let in so little light as only just 

 to make the most luminous part of the spectrum visible, while 

 the rest remains unseen. The feeble intensity of moonlight as 

 compared with sunlight will be most felt with regard to the 

 violet rays and next with regard to the indigo rays. These 

 may be lessened in intensity, so as to make their action un- 

 noticeable under certain conditions, while the red, orange, 

 yellow, and green light may be sufficient to give considerable 

 power to objects of the same or similar colours. 



Poets speak of the "pale moon/'' the "wan moon," the 

 " silver light of the moon," and so forth ; but optically moon- 

 light is generally called yellow. When the moon is seen in 

 broad daylight, it looks like a whiteish cloud upon the sky, 

 and without a decided yellow tint. As evening approaches, 

 and the moon competes in brilliance with the strong but de- 

 clining twilight of summer, she looks yellower, though pale, 

 and a telescope with a low eye-piece, which enables more of 

 her light to reach the eye, makes the yellowness more decided, 

 and a little fog deepens it to a copper red. As twilight fades, 

 and solar light is thus removed from competition and contrast, 

 the moon looks whiter or bluer in fine weather, and many 

 artists make prominent use of blueish grey tints to paint their 

 moonlight scenes. Coleridge speaks of the "yellow moon-lit 

 sea" in one of his poems ; but he probably alluded to a local 

 colour, and did not impute to our satellite the power of throw- 

 ing a yellow tinge over sea of any kind. 



