24- 
PROFESSOR POWELL ON THE DISPERSION OF LIGHT. 
Since in this analysis we know nothing of the values of the coefficients of this series, 
but proceed solely by the elimination of them, it is still possible that in the neglected 
terms we may find the means of explaining the observed discrepancy. In a word, it 
remains an important subject for future research whether a further prosecution of 
the analysis, either by this method or by that which M. Cauchy has himself recently 
pointed out, or that of Mr. Kelland, may not lead to more successful results. 
For the present I will only remark, by way of recapitulation, that upon the whole 
I conceive the formula, as already deduced from the undulatory theory, applies suffi- 
ciently well to the case of media whose dispersion is as high as that of oil of anise 
seed. It also represents, with a certain general approximation to the truth, the in- 
dices of some more highly dispersive bodies. It is therefore extremely probable that 
the essential principle of the theory has some real foundation in nature. While, 
looking at the regularity of the deviation, it seems likely that the formula only re- 
quires to receive some further development 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. 
October 10, 1836. 
