The Science of the Weather 779 



Robinson anemometer is also fitted for recording direction as well 

 as velocity. 



Rain Recording 



The rain that has fallen during any period is registered by 

 collecting the rain in a gauge, which is simply a funnel of circular 

 cross-section with deep edges. From this funnel the rain runs into 

 a collecting vessel, and is measured in a glass graduated to read 

 in hundredths of an inch or in tenths of a millimetre. The gauges 

 or funnels are usually of either 5 or 8 inches in diameter. A more 

 detailed record is obtained by the Hyetograph, or self-recording 

 rain-gauge, of which there are many patterns, most of them 

 registering by the action of the weight of the water collected from 

 the gauge-funnel into a floating vessel to which a pen is attached. 

 When this vessel becomes filled with rain the pen is at the bottom 

 of the chart, and an automatic syphon comes into action, emptying 

 the vessel and preparing it for further recording. 



Sunshine Recording 



The instrument for registering the duration of sunshine is the 

 Campbell-Stokes sunshine recorder. It consists of a metal frame 

 forming half of the central zone of a sphere. Within the arms of 

 this frame there is placed on a small pillar a sphere of glass which 

 acts as a universal lens, whose focus falls exactly on to the inner 

 surface of the frame. The frame is adjusted to the latitude of the 

 station so that the focused image of the sun's path is parallel to 

 the edges of the frame, and in the frame are cut three sets of 

 grooves to hold specially prepared cards that will char without 

 igniting. Owing to the changing altitude of the sun in the sky as 

 the seasons advance, separate types of cards are used for winter, 

 summer, and the equinoctial periods, and these cards are placed 

 in their respective sets of grooves. Whenever the sun shines, its 

 light and heat are focused exactly on to the surface of the card, 

 with the result that a charred trace is left to record the fact. 



