Many workers have used, and still use, the arbitrary scale of the butter refractometer instead of refractive indices to record their measurements. We have therefore had preparedthese tables, by means of which the butter refractometer readings can be readily converted into refractive indices.

They are derived by interpolation from Pulfrich's original equivalents. Although they have been independently arrived at, they prove to be identical with the similar table of Leach, and those of Fryer and Weston, with the exception of a very few differences of one unit in the fourth place of decimals.

Table For The Mutual Conversion Of N And B Readings