. The Bell System technical journal . Vapor-Pressure,ReJative Humidity and Temperature of the Dew-Point from Readings of the Wetand Dry Bulb Thermometers, by C. S. Marvin. Proceedings of the Physical Society of London, Feb. 15, 1922. The Measurementof Atmospheric Humidity, by Sir Napier Shaw. 240 BELL SYSTEM TECHNICAL JOURNAL exposures, and a small exhaust blower was provided for circulatingthe air over the wet bulb. The whole apparatus was controlledelectrically by a clock and was arranged to record the wet and drybulb temperatures at any desired time interval. When the com-plete record roll
. The Bell System technical journal . Vapor-Pressure,ReJative Humidity and Temperature of the Dew-Point from Readings of the Wetand Dry Bulb Thermometers, by C. S. Marvin. Proceedings of the Physical Society of London, Feb. 15, 1922. The Measurementof Atmospheric Humidity, by Sir Napier Shaw. 240 BELL SYSTEM TECHNICAL JOURNAL exposures, and a small exhaust blower was provided for circulatingthe air over the wet bulb. The whole apparatus was controlledelectrically by a clock and was arranged to record the wet and drybulb temperatures at any desired time interval. When the com-plete record roll had been exposed it was removed and upon develop-ment showed the thermometer readings from which the correspondinghumidities could be found in the psychrometric tables. While thist\pe of recorder would no doubt have enabled accurate informa-tion to be obtained, it had two inherent objections. These were,first, the bulkiness of the complete equipment which had to be placedat the location where the conditions were to be determined WWvvWW WtT BULB D«y BULBTHUMOMtTtft TnCRMOMCTCR rig. 1—IJridge Circuit of Difference Recorder second, the thermometers could not be read because their stemswere within the camera box, and therefore, the humidities and tem-peratures measured could not bo ascertained initil the record hadbeen developed. t Accordingh, at this time, consideration was gi\en to a type ofmechanism which would produce a visible record upon a chart con-tinuously a\ailable for observation by the operator. It was foundthat the Leeds & Northrup automatic recorder had been in com-mercial use for some time for the measurement of furnace temperatures,by means of thermocouples in conjunction with an automaticallyadjusted potentiometer circuit. The same t\pe of recorder also had HUMIDITY RECOKl^lh^ 241 I <ii
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