OF METEOKOLOGICAL INSTKUMENTS. 



21 



FIG. 49. 



FIG. 59. 



FIG. 58. 



Although Mason's Hygrometer has for some time been in general use, yet Eegnault's 

 is still much employed for taking direct observations of the dew-point. It consists chiefly of 

 two sensitive thermometers, one exposed to the action of the atmosphere and the other to 

 the influence of a current of air passing through ether. An important part of this instrument 

 is the small polished silver bottle into which, through a stopper, one of the thermometers is 

 inserted. On one side, within the bottle a small silver tube descends nearly to the bottom ; 

 the other end passing outwards is connected with a small flexible aspirating tube. Supporting 

 the bottle is a hollow bent neck connecting it with a telescopic stand that is also hollow, by 

 which the air freely escapes at the base. 



Directions for Using Regnault's Hygrometer. Pour just as much ether into the silver 

 cup as will cover the thermometer bulb, and insert the thermometer as shown in the drawing. 

 On causing the air to bubble slowly through the ether, by breathing through the tube, the 

 immersed thermometer will show a decline in the temperature ; and when a film of moisture 

 forms on the larger part or shoulder of the silver bottle, the temperature at that instant 

 indicates the dew-point. The observer should stand so as not to allow the breath or heat of 

 the person to affect the instrument. 



60. Atmidometer (Dr. BABINGTON'S), for measuring the evaporation from water, 

 ice, or snow; exhibited at the meeting of the Eoyal Society, by Dr. Ba- 

 bington, F.B.S., and explained to the Society in his paper on "The 

 Spontaneous Evaporation from Various Fluids," November 24, 1859. 



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