COLOURS OF FLOWERS. 
51 
purpose is a triangular prism of pure, transparent glass; but it is 
effected by many natural substances, as, for example, by the rain¬ 
drops, which decompose the light, and thus paint the rainbow in 
the heavens ; or the early dew-drops upon the grass, which prank 
the lawn with every tint and every radiance which fancy can 
picture to itself. Different transparent substances decompose light 
in different degrees of perfection ; the colours arising frorn decom¬ 
position by glass being more distinct than those from the same 
process by water, and diamond giving a still more perfect decom¬ 
position. If the light decomposed is a cylindrical beam, admitted 
into a darkened apartment through a circular hole in the window- 
shutter, and the spectrum, as the decomposed light is called, is 
received upon a wall, or screen, at right angles to its centre, and 
parallel to the axis of the decomposing prism, the spectrum is 
extended in the cross direction about five times as much as its 
breadth in the direction of the axis ; and it consists of seven distinct 
colours,—each most intense in the middle, but which so melt 
into each other on their confines, that the entire spectrum contains 
almost every imaginable tint of colour, though seven only are dis¬ 
tinctly apparent. 
These are obviously produced by the different refrangibilities 
of different parts of the beam, the least refrangible lying nearest 
to what would have been the direction had the beam not been 
refracted, and the most refrangible at the opposite extremity of 
the spectrum. Red is the least refrangible, and violet the most 
so ; and from red to violet there are orange, yellow, green, blue, 
and indigo, which, with the red at the commencement and the 
violet at the close, make up the seven. If we suppose the entire 
length of the spectrum to be divided into 360 equal parts, the 
colours occupy the following portions :—red, 45 parts ; orange, 
27 ; yellow, 48 ; green, 60 ; blue, 60 ; indigo, 40 ; and violet, 80. 
On comparing the portions occupied by these colours, it will be 
perceived that the blue edge of the green is exactly in the middle 
of the length ; but as the colours at the violet end are less intense 
than those at the red end, the medium colour is within the space 
occupied by the green, though a little nearer to the blue than 
to the yellow. This medium colour is the one which is best 
adapted to all states of the eye ; and it is worthy of remark that 
this is the general colour of vegetable nature, and the one which 
sets off all the others, and refreshes the eye when it is fatigued 
