The decomposition of white light by prismatic refraction, as effected by Sir Isaac Newton, has, for more than a hundred and fifty years, been received as a demonstrated truth by the most distinguished philosophers of all nations. Various attempts indeed have been made, both in his day and in ours, to overturn this beautiful generalization, but they have been made by persons not only ignorant of the subject, but unacquainted with the first principles of physical research.

The analysis of light by the prism is perfect, in so far as it goes, and was demonstrated by Newton in the case of spectra produced by the single refracting medium which he employed. It was left, indeed, to his successors to discover the different dispersive powers of bodies, and the irrationality of the coloured spaces, and thus to establish the principles of the Achromatic and the Aplanatic Telescopes. These discoveries presented no points of objection to the views of Newton. They were entirely of a supplementary character, and were calculated to establish more firmly his general doctrine respecting the composition of light.