Researches towards establishing a theory of the dispersion of light
The author here prosecutes the inquiry on the dispersion of light which was the subject of his former papers published in the Philosophical Transactions for 1835 and 1830, extending it to media of higher dispersive powers, which alford a severer test of the accuracy of M. Cauchy’s theory. He explains his methods of calculation and the formulae on which his computations are founded, and which are different from those employed in his former investigations: and then states the results in a tabular form. On the whole he concludes that the formula, as already deduced from the undulatory theory, applies sufficiently well to the case of media whose dispersion Is as high as that of oil of anise-seed: or below it, such as nitric, muriatic, and sulphuric acids, and the essential oils ofangelica, cinnamon, and sassafras, balsam of Peru, and kreosote. It also represents, with a certain general approximation to the truth, the indices of some more highly dispersive bodies. The author therefore considers it as extremely probable that the essential principle of the theory has some real foundation in nature. From the regularity which he finds in the deviation of observation from theory, he thinks it likely that the formula only requires to receive some further developement, or extension, in order to make it apply accurately to the higher cases, while it shall still include the simpler form which so well accords with the lower.