The dazzling light emitted from lime intensely heated, known as the Drummond light, gives the colors of the prism almost as bright as the solar spectrum.
If we expose a prepared Daguerreotype plate or sensitive paper to the solar spectrum, it will be observed that the luminous power (the yellow) occupies but a small space compared with the influence of heat and chemical power.

R.Hunt, in his Researches on Light, has presented the following remarks upon the accompanying illustration: [Illustration: Fig.

3 (amdg_3.gif)] "If the linear measure, or the diameter of a circle which shall include the luminous rays, is 25, that of the calorific spectrum will be 42.10, and of the chemical spectrum 55.10.Such a series of circles may well be used to represent a beam from the sun, which may be regarded as an atom of Light, surrounded with an invisible atmosphere of Heat, and another still more extended, which possesses the remarkable property of producing chemical and molecular change.
A ray of light, in passing obliquely through any medium of uniform density, does not change its course; but if it should pass into a denser body, it would turn from a straight line, pursue a less oblique direction, and in a line nearer to a perpendicular to the surface of that body.

Water exerts a stronger refracting power than air; and if a ray of light fall upon a body of this fluid its course is changed, as may be seen by reference to Fig.

4.
[Illustration: Fig.