A study of direct-current corona in various gases

1. The critical corona intensities have been determined for helium, hydrogen, oxygen, nitrogen, air, and carbon dioxide for pressures ranging from 2 to 760 mm. 2. In each case the relation was found to hold approximately for pressures above 4 cm. 3. The values found for air agree well with those found by Whitehead and Isshiki from their investigation of alternating-current corona. 4. No simple relation could be found giving the correction between over the whole range of pressure. 5. The influence of temperature on critical corona intensity was investigated for hydrogen, and found to consist merely of a change in 0, as was expected. 6. It is shown that the data obtained do not permit the explanation of corona as a process of ionization by collision, unless we make further assumptions. The nature of the assumptions necessary is not evident.