Electron Temperatures Derived from Observations of Low-Density H II Regions and Planetary Nebulae

New observations of the X 4363 and N1 lines of [0 iii] in two low-density diffuse nebulae and three low-density planetary nebulae are reported. The results are used to derive accurate electron temperatures. It is shown that the role of collisional cooling does become increasingly important in lowMensity gaseous nebulae. The comparison of observed and predicted electron temperatures for H ii regions generally supports the models of Hjellming and the smaller collision strengths calculated by Osterbrock for levels giving rise to infrared cooling.