The absolute fluorescence quantum yield of quinine bisulphate in aqueous 1N H2S04 with excitation at 366nm has been measured calorimetrically. A value of 0.561 is reported with an error conservatively estimated at 7 %.

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It is shown how the formula ordinarily used to compute the quantum yield of luminescence relative to that of a ’’standard’’ substance should be changed in order to take account of polarization effects in the excitation monochrometer and emission spectrometer, as well as nonzero emission anistropy of the emitting systems. A simplification results in a ’’correction factor,’’ and the magnitude of this factor, calculated for systems with varying degrees of emission anistropy, is seen to be outside of experimental error for highly viscous systems.