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
${E \over P} = A + {B \over \sqrt{P}}$
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
${E \over P} \ {\rm and} \ {1 \over \sqrt{P}}$
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.