Another beautiful grotto has green instead of blue refractions; the effect in both cases is due to the light entering by a small entrance.
Although establishing certain general relations between atomic and molecular refractions, the results were somewhat vitiated by the inadequacy of the empirical function which he employed, since it was by no means a constant which depended only on the actual composition of the substance and was independent of its physical condition.
Compounds having the same composition, have equal molecular refractions, and that equal differences in composition are associated with equal differences in refractive power.
Atomic refractions may be obtained either directly, by investigating the various elements, or indirectly, by considering differences in the molecular refractions of related compounds.
Hydroxylic oxygen is obtained by subtracting the molecular refractions of acetic acid and acetaldehyde.