Theory of effect of potential gradient on measurements with the Ebert ion-counter.—In a former paper, the theory of the action of the negative charge induced on the ion-counter by the normal atmospheric potential gradient in causing error in the measurements of the negative ion-density was worked out for the case where the induced charge is insufficient to prevent the entry of ions at any point. The theory led to a linear relation between the reduction in measured negative ionic density and the potential-gradient. The simple theory is now extended, to take account of the action of the induced charge in not only changing the speed of the ions but in reducing the area of the surface through which negative ions can enter the instrument. Assuming a simple ring distribution of the induced charge, an expression for the variation of percentage error or reduction in the measured negative ionic density with potential-gradient, is derived, and shows a non-linear law, in general agreement with the observations of Mackell. In measurements of positive ion-density, the extended theory, like the simple one, indicates that no error is to be expected, for a potential-gradient of normal sign, a conclusion confirmed by recent results of Mackell and of Norinder.

Close

PrevNext

View figure in article