Page:Gods Glory in the Heavens.djvu/151

Rh of results, but no doubt exists as to the incalculable value of the new analysis.

When a ray of white light is passed through a prism, it is separated into the various colours of the spectrum, viz., red, orange, yellow, green, blue, indigo, and violet. It is thus shewn, that the white ray is compound—and that the prism decomposes this ray into the variously-coloured constituent rays. If we compare the white ray to a closed fan, the opening of the fan will represent the effect of the prism, in spreading out and representing separately the constituent rays. We shall suppose the fan to consist of seven ribs or sectors, representing the seven primitive colours; when the fan is shut, these colours are not visible, but when it is opened it represents the spectrum of white light. A ray of white light may, also, be compared to a rope, made up of strands of the various colours of the spectrum, and the prism serves, by refraction, to open up the rope and present the strands separately. Perhaps a still better illustration is to compare the white ray to a quantity of sand, composed of seven differently-coloured kinds. In this case, the prism separates the different kinds of sand, and assorts them in distinct coloured layers—there being always a regular gradation from the red to the violet. The position of the various colours in the spectrum is perfectly fixed. The fan may be opened more or less, but the relative positions of the ribs are, always the same. In the case of other colours