Abstract

Recorder Mechanism.—A mechanism is described capable of automatically balancing any network of impedances where the balance point is attained by the motion of one or more sliders along slide wires, and where the balance point is determined by the absence of current in the recorder galvanometer.

Relative Humidity Curves.—From the formula for relative humidity in terms of the wet and dry bulb temperatures, it is shown that for constant humidity the relation between wet and dry bulb temperatures is very nearly a linear one, and that the value of the humidity is uniquely defined by the ratio (wet bulb temp.—A)/(dry bulb temp.—B) where B is a constant and A is a function of the relative humidity but changes only slightly with it.

Recorder Circuit.—By using a nickel resistance thermometer in a network which is essentially a split circuit potentiometer, it is possible to secure a potential difference across the ends of a slide wire which is directly proportional to (dry bulb temp.—B). In another very similar circuit a potential difference is gotten which is proportional to (wet bulb temp-A). This latter potential difference is automatically balanced against a portion of the former by the recorder mechanism mentioned above, and the position of balance is indicative of the ratio (wet bulb temp.—A)/(dry bulb temp.—B) so that the instrument reads directly in relative humidity.

The results of a check on the finished instrument are given from which it appears that the approximations made in the design and any inaccuracies introduced in the actual construction are of no greater magnitude than the uncertainties in the humidity formula itself.

Maintenance of Wet Bulb.—Two forms of wet bulb are described which are capable of continuous operation. In one the customary wick is replaced by a spray, and in the other a long wick is provided so that a clean portion can be substituted for the soiled part merely by turning a roller to wind the wick from one holder on to another.

© 1926 Optical Society of America

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