74 



THE PRISM. 



by letting the coloured rays, which have been separated by a ^ 



prism, fall upon a lens, which will converge them to a focus, ) 



and, being thus re-united, will appear white as they did before ] 



refraction. ] 



Prisms are commonly made of solid glass, but those who i 



do not possess one of this kind may easily make a substitute. -^ 



Take three pieces of plate glass, each four or six inches ; 



long, and two or three inches wide : procure a tin frame, i 



the two ends of which are in the exact shape of the three j 



pieces of glass placed in the form of a triangle, with a strip j 



of tin running from each angle of one end to the angles or | 



corners of the other. These strips are bent so as to receive | 



the two edges of the glass plates. The tin forming the ends | 



is turned up so as to receive tlie plates, and one of the ends \ 



is furnished with a little tube to pour in water. When the | 



frame and the glass plates are fastened together, and the ere- 1 



vices stopped, the prism is filled with clear water, and is \ 



ready for experiment. I 



When a spectrum is formed by the light which has pass- j 



ed through a prism upon a skreen, if a small hole be made \ 



through the skreen, and the rays of one colour only be per- J 



mitted to pass through it, then whatever is viewed in that \ 



light, will appear of that particular colour. Thus if red 1 



light only has passed through the hole, then blood, or grass, j 



or milk, viewed in tha* light behind the skreen, will appear • 



red ; excepting that the blood will appear of a stronger red .^ 



colour than the grass or milk. If the blue light only has| 



been transmitted through the hole, then the above men- | 



tioned substances will appear blue ; and the like must be j 



understood of the other colours. This proves that the \ 



colours, which seem to proceed from coloured bodies in ge- \ 



neral, do not belong to those bodies ; but they are the com- \ 



ponent parts of the white light, in which those bodies are ? 



viewed, and that certain bodies have the property of absorb- \ 



ing some of those coloured rays of the white light which ^ 



falls upon them, and of reflecting others. Thus, grass re- - 



fleets the green rays and absorbs the rest ; hence, the green J 



rays coming to our eyes, render the uppearaTice of grass , 



green ; thus blood absorbs every other coloured ray except- \ 



ing the red, and so forth. Black bodies absorb all the seven^^ 



coloured rays, and white bodies reflect them all. Providence ^ 



appears to have decorated nature with the enchanting di- , 



