THE FARMER'S MAGAZINE. 



99 



We see, then, that even the rain-drops were weighed 

 by their Divine Author, their gravity adapted to 

 the powers and good of His creatures, and the bed 

 of earth on which they were to descend and fer- 

 tihze. The mean annual fall of rain on the entire 

 surface of the earth is estimated at about five feet 

 (Maury, Phy. Geo. Sea, 207) ; but the amount 

 of the average annual fall of rain varies, however, 

 widely in different countries, from the districts of 

 the Andes, where the ram rarely ceases, to those 

 not a hundred miles distant, around Lima where 

 rain is almost unknown. 



In our quarter of the globe, the annual rainfall 

 varies with different countries, altitudes, and ex- 

 posures to moist westerly currents. At Madrid, 

 which is placed on an elevated plateau, the annual 

 rainfall is only about 10 inches. At Coimbra, in 

 Portugal, a fall of more than 200 inches has been 

 recorded. Extraordinary rainfalls have occurred 

 occasionally in the South of Europe. On October 

 25, 1825, 32 inches fell at Genoa, and October 9, 

 1827, at Joyeuse, in the south of France, 31 inches 

 fell. In the East Indies 13.06 inches fell at Maha- 

 buleshwur, September 2, 1833 ; but 11 or 12 inches 

 is not rare. In July, 1840, 134.42 inches fell at 

 that station. At Bombay, July 1, 1844, 7.44 inches 

 fell in twenty-four hours, 2 inches falling in seventy 

 minutes {ibid, p. 366). In England our rainfalls 

 do not nearly approach amounts like these. Mr. 

 E. J. Lowe has recorded the most rainy months 

 and days at Beeston, near Nottingham, from 1843 

 to 1857 :— 



MOST RAINY MONTHS. 



In our country, the smallest rainfall is in Essex, 

 which hardly averages 20 inches. The largest is 

 in the westerly counties, where it ranges from 35 to 

 46 inches. On some of the mountains in West- 

 moreland 108 to 148 inches have been recorded in 

 one year. 



ITS ORIGIN AS VAPOUR. 



Having noted the fall of rain — seen it descend 

 from the clouds — the next portion of our inquiry is. 

 How did that rain water get into the atmosphere ? 

 We need hardly be reminded that it was by the 



evaporation of water from the earth's surface. "To 

 evaporate," observes Maury, in his valuable work 

 on the Physical Geography of the Sea, " water 

 enough annually from the ocean to cover the earth 

 to a depth of rive feet with rain-water, to transport 

 it from one zone to another, and to precipitate it 

 in the right places at suitable times and in due 

 proportions, is one of the grand offices of the 

 atmosphere." This water is evaporated chiefly 

 from the torrid zone. Supposing it all to come 

 thence, to raise as high as the clouds, and to lower 

 down again, all the waters in a lake sixteen feet 

 deep, three thousand miles broad and twenty-four 

 thousand long, is the annual business of this in- 

 visible machinery. Well may we exclaim. What a 

 powerful engine is the atmosphere ! And how 

 nicely adjusted must be all its cogs, and wheels, 

 and springs, and compensations, that it never 

 wears out, or fails to do its work at the right time 

 and in the right way 1 "According to Laidly," 

 adds Maury, " the evaporation at Calcutta is about 

 15 feet annually; between the Cape of Good Hope 

 and Calcutta it averages, in October and Novem- 

 ber, nearly three-quarters of an inch daily ; be- 

 tween 10 and 20 degrees in the Bay of Bengal it 

 was found to exceed an inch daily. The South 

 Seas then should supply the atmosphere with 

 watery vapour, while the northern hemisphere con- 

 denses it. We should therefore have more rain in 

 the northern hemisphere. The rivers tell us that 

 we have, for the great water courses of tire globe, 

 and half the fresh-water in the world, are found on 

 our side of the equator. The rain gauge also tells 

 us the same story. The average fall of rain in 

 the north temperate zone, according to Johnstone, 

 is 37 inches : he gives but 26 inches in the south 

 temperate. The observations of mariners corro- 

 borate this conclusion. Rains, fogs, thunder, 

 calms, and storms, all occur much more frequently, 

 and more irregularly on this side, than they do on 

 the other side of the equator. 



Let us begin our examination by finding out the 

 ordinary amount of vapour present in the air, and 

 with what gases it is mixed. The composition of 

 the atmosphere, at a mean temperature and pres- 

 sure, is as follows : — 



By measure. By weight. 

 Nitrogen gas .... 77.5 .... 75.5-5 



Oxygen gas .... 21.0 23.32 



Aqueous vapour ., 1.42 .... 1.03 

 Carbonic aod gas.. 0.08 .... 0.10 



Whoever wishes to see that aqueous portion of 

 the atmosphere made apparent to his senses, need 

 only introduce a glass of very cold-water into a 

 warm well-tenanted room — the vapour of its at- 

 mosphere is immediately condensed on the glass. 

 It is not, as is commonly said, the heat of the air, 

 but its warm aqueous vapour, that strikes, that is 

 condenses upon the glass. 



The state in which water exists in the atmos- 

 phere seems now pretty well determined. It was 

 formerly supposed, by the majority of philosophers, 

 that it was in a state of chemical combination with 

 the atmospheric gases ; but later researches seem to 

 show that it is in the state of steam. Saussure long 



H 2 



