Treatise on heat / By the Rev. Dionysius Lardner.

  • Lardner, Dionysius, 1793-1859.
Date:
1833
Catalogue details

Licence: Public Domain Mark

Credit: Treatise on heat / By the Rev. Dionysius Lardner. Source: Wellcome Collection.

    308/446 (page 296)
    SS, as it would do, if it did not encounter the glass, it is deflected upwards in another direction, forming an Fig. 33. angle with its original course. Now it is found that the ray thus bent upwards does not continue to form one line of white light as before, but it spreads or diverges, and, if received on the screen, instead of illuminating a single spot, as it would do if it were not intercepted by the prism, it covers an extended line on the screen from V' to R; and tlie lengtli of tliis line increases if tlie screen be moved from tlie jirism, and decreases if the screen be moved towards the prism, a necessary consequence of tlie divergence of the rays issuing from the prism. It is also observed, that this line of light, thus produced on the screen, is not a uniform white light like the sjiot which would be produced on a screen held between A R C! and the window shutter. (Jn the other hand, an appearance is produced of a regular succession of brilliant colours, the highest colour, \’, being violet, the next below this indiyo, which is succeeded by blue, green, yellow, orange, and finally red, in regular succession, each colour occupying a certain space in the line of light. This effect is commonly called the prinniatic spectrum, and it de- pends on two facts which are ascertained in optics, namely, — first, that the ray of light SS is compounded of several distinct rays, which differ from each other in