THE FARMER'S MAGAZINE. 



101 



1842. 1843. 



Depth of rain in inches 26.11 24.9 



Evaporation 21.56 2G.11 



Filtration 4.55 4.2S 



It is noticeable from these trials how much 

 greater is the evaporation from the hmestone than 

 from the chalk ; and how much less the drainage. 

 The winds produce afar more considerable amount 

 of evaporation than the mere heat of the sun. The 

 marine-salfc makers, wlio expose sea-water, in very 

 shallow ponds, to the action of the atmosphere, 

 are well aware how much faster the Summer 

 breezes evaporate the water than the sun on a still 

 day ; every washerwoman is aware of the same 

 fact, Mr. Charnock experimentalized upon this 

 question ; he found that — 



1842. 



1843. 



33.61 



The annual evaporation from ■\ 



water to both the sun (^ 



and the wind was, in i 



inches / 



From water exposed to the "^ 



wind, but shaded from the > 22.48 



sun , J 



From a drained soil 21.56 20.11 



From a soil saturated with 



water 



30.02 



34.17 



22.72 



31,19 



But it is not only the surface of the earth and its 

 waters from whence the insensible moisture of the 

 atmosphere is derived. Plants contribute, and 

 copiously too, to the supply. It is certain that 

 plants of all kinds exhale moisture in large propor- 

 tions. Mr. G. Phillips {Jour. R. A. S., vol. vh., 

 p. 306) found that a polyanthus, placed in a pot of 

 earth, between the 28th of February and the 14th 

 of April, 1845, evaporated 2.01 grains of water 

 daily for every sqare inch of the surface of its 

 leaves, and the mould 10.8 grains for every inch 

 of surface : he found that a fine day, with sun and 

 wind, always promoted evaporation, while a dull 

 cold day always retarded, or stopped it. The evapo- 

 ration from the leaves of a potato, under similar 

 circumstances, was much less, being at the rate 

 of only 1.4 grains per day for each square inch of 

 surface. The transpiration of moisture from plants 

 increases progressively from March to August, 

 after which period it declines. It is the most 

 copious from sunrise till noon, after which hour it 

 lessens. Other plants emit moisture at a much 

 greater rate than the polyanthus or the potato. 

 Hales found that the sunflower transpired, in July 

 and August, 15 grains of water from every square 

 inch of its surface ; a cabbage, under favourable 

 circumstances, has been found to emit, daily, water 

 equal to its own weight. 



Need we attempt to calculate the enormous 

 amount of aqueous vapours which the vegetable 

 world thus contributes to our atmosphere ? the 

 whole covering of our Emerald Isles pouring in an 

 incessant stream of moisture ; the vegetation of all 

 lands contributing their portion. The dense 

 steaming forests of the equatorial regions adding 

 perhaps the largest amount in a given space; enor- 

 mous, though insensible streams, rivalling in their 



weight of water those of the Amazon and the Mis- 

 sissippi. From the vegetation of the whole world 

 in every clime, in every soil, and at every altitude, 

 from the level of the sea up to the lines of eternal 

 snow, by day andby night, is this outpouring going 

 on ; no winds prevent its continuance, by no 

 change of temperature is this invisible stream of 

 watery vapour entirely stayed. 



But the emission of vapour into the air by the 

 surface of the earth, its waters, and its vegetation, 

 are not the only sources of the supply of atmo- 

 spheric moisture. All animals contribute a consi- 

 derable share. As I have elsewhere had occasion 

 to remark, the evaporation from the surface and 

 from the lungs of animals is very considerable : it 

 varies, however, in different species and individuals. 

 Cruickshank calculated it, from his experiments, 

 to average about 7 pints, in a man, during the 24 

 hours; Lavoisier and Seguin made it amount to 

 only 3] pints, the maximum bemg 5lbs., the mi- 

 nimum ijibs. They calculated that, in every 18 

 parts of water thus evaporated, 7 parts were from 

 the lungs, and 11 from the skin. Its amount is 

 increased by drink, but not by solid food. Its 

 minimum amount is immediately after a meal, and 

 in close, foggy weather : it attains its maximum 

 during digestion. It is, as might be expected, the 

 most considerable in warm and breezy weather, in 

 hot climates, and after great exercise. This is in- 

 dicated by the enormous quantity of hquid con- 

 sumed by those who labour under such circum- 

 stances; the daily 14 pints of beer, the 24 pints 

 of cider, allowed to the reapers {Jour. Roy. Ag. 

 Soc, vol. xiv., p. 445) ; and by the 30 pints of 

 porter swallowed by the London coalwhippers — an 

 amount which is often unequal to the loss they 

 sustain by transpiration. The evaporation from a 

 labourer, in certain situations, is, in fact, enormous. 

 Dr. Southwood Smith made some observations 

 upon the men employed in emptying and filling 

 th« retorts at the Phoenix Gas Works. These men 

 are thus engaged for one hour twice a day. On a 

 foggy day in November, when the temperature of 

 the external air was 39 deg., the greatest loss of 

 weight by these men, in an hour and a quarter, 

 was 2lbs. 15 oz. ; and the average of eight men 

 was 2lbs. 1 oz. On a bright day in the same 

 month, when the temperature of the surrounding 

 air was 60 deg., the greatest loss of weight was 

 41bs. 3 oz., the average loss being 3lbs. 6 oz. On 

 a bright, clear day in June, the greatest loss sus- 

 tained in the hour, by a man who had worked in a 

 very hot place, was 5lbs, 2 oz. ; the average of all, 

 2 lbs. 80Z. 



Such are the chief sources of the vast fountains 

 of vapour which replenish the atmosphere with the 

 water, that we shall presently trace becoming 

 visible to our senses, in clouds, in dew, and in the 

 rain-drop. The atmosjihere in which we are en- 

 veloped, and in which, and by which, we live, is, 

 indeed, full of marvels abounding with evidences 

 of design, and the benevolence of its Creator. It 

 is such testimonies that our readers may profitably 

 study, not only in their fields, but by their study- 

 fire ; and as an able American author, whom I 

 have before quoted, remarks, in one portion of his 

 excellent work, "to him vkho studies the physical 



