Text-book of medical and pharmaceutical chemistry . hide of carbon. Insome instruments there are several flint glass prisms so arrangedthat the light is made to pass through all of them, so as to securea wider dispersion of the rays than can be obtained with one beam of light, after traversing the prisms, is viewed with thetelescope (B). For purposes of comparison, an additional tube(C) is attached, by which another light may be thrown upon thesurface of the prism so as to be reflected through the telescope LIGHT. 35 by the side of the light from F.* Many instruments now madeare so a
Text-book of medical and pharmaceutical chemistry . hide of carbon. Insome instruments there are several flint glass prisms so arrangedthat the light is made to pass through all of them, so as to securea wider dispersion of the rays than can be obtained with one beam of light, after traversing the prisms, is viewed with thetelescope (B). For purposes of comparison, an additional tube(C) is attached, by which another light may be thrown upon thesurface of the prism so as to be reflected through the telescope LIGHT. 35 by the side of the light from F.* Many instruments now madeare so arranged that the ray of light in passing through the prismis not bent from its course, and these are called direct visionspectroscopes. 38. Bright Lines.—When we view mono-chromatic lightwith the spectroscope—that is, a light composed of but one color,we see only a vertical image of the slit in B, and its position willdepend upon the refrangibility of that color. If, on the otherhand, we illuminate the slit with a light containing several rays. of different degrees of refrangibility, we shall see one image foreach ray present; and they will be separated from one anotherby their differences of refrangibility. The same color alwaysappears in the same position with reference to the others. If welook at a solid body, heated till it emits a pure white light, therewill be so many images spread out on the field of vision that theone overlaps the other until there are no dark spaces betweenthem, and thus give a continuous spectrum, as it is we place a light before the slit which emits very little light of * For an explanation of the principle of lenses the student is referred toworks on Physics. 36 MEDICAL CHEMISTRY. its own, such as that given by a Bunsen burner, and then putinto this flame a little sodium, which gives a pure yellow light,we shall see but one image of the slit, and that in the positionoccupied by the yellow in the continuous spectrum, or the Dline in the
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