Moonlight and Colour. 129 



suggest to the readers of the Intellectual Obseevee a series 

 of pleasing and instructive experiments, which may occupy 

 some happy hours during the glorious nights of the autumn 

 and winter moon. Moonlight differs chiefly from sunlight in 

 the matter of intensity, and also, to a variable and not easily 

 definable extent, in the matter of colour. Sir John Herschel 

 observes that if a ball of quicklime ignited in. the oxy-hydrogen 

 flame, and producing the most intense artificial light, be held 

 between the eye and the sun, and both viewed through a dark 

 glass, the f lime ball appears like a black spot on the face of our 

 great luminary, so great is the difference between the intensity 

 of the two lights. He adds that it would require 146 balls of 

 quicklime, each the size of the sun, to equal his illuminating 

 power. As a result of this intensity of solar light and of the 

 refractive power of the air, the colour, as well as the form, of 

 objects can be seen in ordinary day-time out of the direct line of 

 the sun's beams. When a coloured object is placed in full 

 sunlight it becomes brighter, but does not look changed unless 

 its surface is highly reflective and seen at a certain angle, and 

 then it may seem luhite, as the black wings of rooks occa- 

 sionally do when they occupy a particular position with reference 

 to the sun and the eye of the observer. 



On a sunshiny morning take two books or pieces of paper, 

 one bright blue and the other bright red, out in the open air, 

 and place them in the sun's beams. Both look very brilliant, 

 and the contrast between them is very striking. Next place 

 them close together so as to make a continuous surface, and 

 the discrepancy of colour becomes more striking. Then take 

 a narrow stick, and hold it an inch or two above the books, so 

 that one half its shadow falls on the red one and the other half 

 on the blue. The shadow will be sufficiently transparent to 

 enable the blue and red to be discerned through it, but for 

 want of light the colours will be so enfeebled that nothing that 

 can be called a contrast will be observed in the two portions 

 of the shadow line. 



In the next experiment place three books, bright blue, red, 

 and green, on the ground in full sunlight, stand upright and 

 hold a lono- ruler so as to throw its shadow across the three. 

 In this case the shadow will be much lighter than in the pre- 

 ceding, as more diffused light is able to get at the parts 

 excluded from the direct rays. Upon the red book the shadow 

 will appear of a purplish black hue, though not deep ; upon 

 the blue book it will look bluer from the transmission of blue 

 light through it ; and upon the green book it will look greener 

 from the same cause. A yellow book, under such circumstances, 

 behaves similar to a red one. Thus, diminishing the light by a 

 shadow has affected the bright red book more than the bright 



