Figure 26. Six- inch plastic rain gage. 



h. Sling Psychrometer . A sling psychrometer is used to measure relative 

 humidity and to determine the dew point (Fig. 27). The psychrometer has two 

 thermometers mounted in a frame which can be rotated rapidly. A moistened mus- 

 lin wick is attached to the bulb of one of the thermometers and the device is 

 whirled to ventilate both thermometers. The temperature is read from both the 

 "wet" and the "dry" bulb thermometers and a set of tables is used to obtain the 

 relative humidity and dew point values from the different temperatures. The 

 dew point is recorded daily along with the other meteorological observations. 

 Additional details on the sling psychrometer can be provided by the Basic 

 Observations Branch, NWS. 



i. Mechanical Pyranograph . This device, located on top of the weather 

 instrument shelter and made by the Weather Measure Corporation, Sacramento, 

 California, provides a continuous record of the intensity of the sun and sky 

 radiation (Fig. 28). Two black and two white bimetallic strips are coupled to- 

 gether with the black strips attached through a linkage to the recording pen. 

 As the radiation heats the black strips, the pen deflects. The white strips 

 provide compensation for ambient temperature changes. The area under the curve 

 on the chart record is a measure of the total radiation. The chart records are 

 collected and stored without analysis. 



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