90 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, E.G. 



FIG. 103. 



FIG. 104. 



of doors, freely exposed to the action of the atmosphere ; after exposure, the 

 water is again measured, and the difference between the first and second 

 measurement shows the amount of evaporation that has taken place. If rain 

 has fallen during the exposure of the evaporating dish, the quantity collected 

 by a rain gauge must be deducted from the amount of the measured contents 

 of the evaporating dish when the observation is made. The wire cage round 

 the gauge is to prevent animals, birds, &c., from drinking the water. 



Price, with Graduated Measure . . : 136 



127. Atmidometer* (Dr. Babington's), fig. 104 for measuring the evapo- 

 ration from water, ice or snow. Consists of an oblong hollow bulb of glass or 

 copper, beneath which, and communicating with it by a contracted neck, is a 

 second globular bulb, duly weighted with mercury or shot. The upper bulb is 

 surmounted by a small glass or metal stem, having a scale graduated to grains 

 and half-grains ; on the top of which is fixed horizontally a shallow metal pan- 

 The bulbs are immersed in a vessel of water having a circular hole in the cover 

 through which the stem rises. Distilled water is then gradually poured into 

 the pan above, until the zero of the stem sinks to a level with the cover of the 

 vessel. Thus adjusted, as the water in the pan evaporates, the stem ascends, 

 and the amount of evaporation is indicated in grains. This instrument affords 



* M r. Scott suggests that Leslie's term Atmidometer is more classically correct, but that Atmometer 

 has the advantage of being shorter, without being absolutely incorrect, 



