The spectroscope and its work / [Richard A. Proctor].

  • Proctor, Richard A. (Richard Anthony), 1837-1888.
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: The spectroscope and its work / [Richard A. Proctor]. Source: Wellcome Collection.

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    structure or density, has the direction of its path more or less altered. Rays of different colour being differ- ently affected when thus deflected, or refracted, as it is called, can be separated from each other by submitting them to suitable processes of refraction. What, then, we have first to do, rightly to understand the work of the spectroscope, is to examine the nature and laws of the refraction of light, and to distinguish refraction from other processes which light may undergo. When light falls on an opaque polished surface, the rays are reflected according to a simple law. Thus, if the ray R I (fig. 1) fall on the polished surface AB at I, it will be reflected on the course I S, such that the angle R I Q, be- tween I R and the perpendicular I Q, is equal to the angle S I Q between IS and the same per- pendicular. So that if A S R B be a semicircle, having I as centre, the arc A S is equal to the arc B R. A fraction of the light falling on A B, however, illuminates this surface and makes it visible, some of the rays being irregularly reflected from the various particles composing the surface. The less polished the surface the greater will be the proportion of rays thus scattered to those regularly reflected. A portion of the light is also absorbed by the sur- face, the proportion of the rays thus absorbed depend- ing on the nature of the surface. The surface also may absorb more rays of some colours than of others, and thus the rays by which it is seen will not be pro- portioned in the same way, as to colour, as those falling Fig. 1.—Illustrating the law of the reflection of light.