[en] A device for detecting ionising radiation and measuring its intensity is claimed. It comprises a sealed vessel enclosing dry air or other gas. Two conducting surfaces, one fixed, the other pivoted, are suspended in the gas. They are supported in such a manner that a static charge can be transferred to them from a charged body without but the same charge cannot return except through the enclosed gas. The electrical conductivity of the gas is affected by the presence of ionising radiation in proportion to its strength