Fifth book of lessons for the use of schools . or white. Sir Isaac Newton, to whom we are indebted for themost important discoveries respecting light and colours,was the first who divided a white ray of light, andfound it to consist of an assemblage of coloured rays,which formed an image upon the wall, such as is ex-hibited, in which are displayed the following series ofcolours—red, orange, yellow, green, blue, indigo, andviolet. Now a prism separates these coloured rays byrefraction. It appears that the coloured rays havedifferent degrees of refrangibility; in passing throughthe prism, theref
Fifth book of lessons for the use of schools . or white. Sir Isaac Newton, to whom we are indebted for themost important discoveries respecting light and colours,was the first who divided a white ray of light, andfound it to consist of an assemblage of coloured rays,which formed an image upon the wall, such as is ex-hibited, in which are displayed the following series ofcolours—red, orange, yellow, green, blue, indigo, andviolet. Now a prism separates these coloured rays byrefraction. It appears that the coloured rays havedifferent degrees of refrangibility; in passing throughthe prism, therefore, they take different directions,according to their susceptibility of refraction. Theviolet rays deviate most from their original course;they appear at one end of the spectrum, A B. Con-tiguous to the violet are the indigo rays, being thosewhich have somewhat less refrangibility; then follow, in * This will at oDce appear, as in the case of the lens, by drawingperpendiculars to the surface of the« prism where the ray entersand quite 344 FIFTH BOOK. succession, the blue, green, yellow, orange, and lastly,the red, which are the least refrangible of the colouredrays. The union of these colours, in the proportions inwhich they appear in the spectrum, produces in us theidea of whiteness. If a card be painted in compart-ments with these seven colours, and whirled rapidly ona pin, it will appear white. But a more decisive proofof the composition of a white ray is afforded by re-uniting these coloured rays, and forming with them aray of white light. This can be done by letting thecoloured rays, which have been separated by a prism,fall upon a lens, which will make them converge to afocus; and when thus re-united, they will appear white,as they did before refraction. The prism, p, separatesa ray of white lightinto seven colouredrays; and the lens, ll,brings them to a focusat F, where they againappear white. Thus by means of a prism and a lens, we can take a ray of whitelight
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