Photoelectric measurements are given of the fluxes in H and in the [0 iii] Ni and N2 lines fwm eleven planetary nebulae with small angular diameters. The observations were made with a scanning spectrograph on a 36-inch reflector, and the calibration into energy units was provided by of stars with previously measured continuous spectra. Measurements of the fluxes in H and Ni from fourteen planetary nebulae with larger diameters are also given. These observations were made with interference filters and a photoelectric photometer on a 12-inch reflector, and the calibration was provided by observations of small planetaries with previously measured fluxes. All published photoelectrically measured fluxes from planetary nebulae are collected, and approximate corrections for interstellar reddening are applied. There is a good correlation between the corrected average surface brightness of a planetary in H and its average electron density as estimated from the [0 iij 3729/X 3726 intensity ratio This correlation has the form expected from the hypothesis that all planetaries have essentiafly the same mass but differ in stage of expansion.