Hesults of Some Experiments upon the Bate of Evaporation. 45 



under given climatic conditions a restricted capillarity reduced the 

 rate of evaporation by 22 per cent. 



Without claiming that capillarity is responsible for all the increase 

 of evaporation shown by an unpainted, as compared with a painted 

 gauge, it seems likely that some of the high numbers indicated by 

 the small gauges at Strathlield Turgiss were due, in great part, to 

 this source of error. 



At Camden Square, London, Symons tried three gauges : — 



I. A cylinder (material not stated), 5 inches in diameter and 5^ 

 inches long, resting on the neck of a stone bottle, part of the body 

 of which was sunk in the ground so that the rim of the evaporator 

 was a foot above the surface of the ground. It is described as " an 

 excellent arrangement for enabling the sun to heat the water as 

 much as possible." 



II. A black japanned tin cylinder, 5 inches in diameter, 1 foot 

 long, buried 9 inches in the earth. "The cheapest possible evapo- 

 rator, partly protected against heating, but too small and unduly 

 affected by the sides, which must be high to prevent out-splashing 

 ^nd overflow." 



III. A glass vessel, 5 inches in diameter and 9 inches deep, 

 placed inside a tub of water — 15 inches in diameter and also 9 

 inches deep — so that that inside the cylinder was always surrounded 

 by water up to the same level. The rim of the tub was just above, 

 and the surface of the water approximately flush with, the ground 

 line. "A repetition of Major Phillips's, insplashing and outsplash- 

 ing nearly balance, but it breaks at the first frost." 



From July 22 to November 19, 1869, the results were : — 



Gauge. 



Water Evaporated. 



Ratio Evaporated. 



I. 



II. 



III. 



15*75 inches 

 13-57 „ 

 0-72 „ 



162 

 140 

 100 



From July 22nd to August 12th the results were 



Gauge. 



Water Evaporated. 



Ratio Evapo- 

 rated. 



Average Excess of 



Temperature 



above 65°. 



Temperature 

 Ratio. 



I. 



II. 



III. 



2-46 inches 

 3-13 „ 

 4-37 „ 



178 

 127 

 100 



15-7° 



10-8 



8-8 



178 

 123 

 100 



