Abstract
For the purpose of direct indication or recording of humidity, it is reasonable and convenient to use the selenium hygrosensitive elements, formerly developed by the present authers, Saito and Serizawa, inserted in A. C. circuits. In this case, requirements on the characteristics of the elements must be somewhat different from those used in D. C. circuits.
In this paper, manufacturing methods and properties of such purposive hygrometer elements are reported in the first place. Then two different types of electrical instruments directly indicating humidity are introduced. One is A. C. resistancemeter type and the other is automatic balancing A. C. bridge type. They are selectively applicable for the purpose of humidity measurement.
