THE FARMERS' REGISTER. 



523 



fully must be considered in a very special way, i Mr. J)aniell (ells us that the " moisture of the air 

 and in such detail as can only be expected in a llovvin«,' from any point between n. e. and s. e. 



An idea of the inclusive, is, to that o( the air from the other 



separate work upon the subject 

 difference between the atmospherical moisture ot 

 London and that of other parts of the world may, 

 however, be collected from the fbllowingltat)le, 

 showing the amount of rain that jails in a lew 

 different countries : 



Inches per annum 



London 



St. Petersburg 



Algiers 



Fattehpur (E. Indies) 



Madeira 



Sagar (E. Indies) 



Bahamas 



Calcutta 



Ceylon 



Macao 



Equator 



Coast of Malabar 



Grenada 



Leogane, St. Domingo 



24.01 average of 10 years. 



16. 



27. 



35.94 average of 4 years. 



31. 

 from 31.15 to 64.76 



54.99 

 from 59.83 to SI. 



84 3 

 from 4S.8 to 107.3 



96. 



123.50 average of 14 years. 



126. 



150. 



Bengal, 20 to 22 inches in a single month. 



Bombay, 32 inches in 12 days. 

 Tavoy, 203.5 inches in six months ; as much as 

 8.5 in a day (July 31, 1S31.)* 



We possess, to a certain extent, the power of 

 modifying the moisture of the air even in the open 

 air, and have almost complete control over that of 

 glazed houses. 



li is found by experience that the effect of wind 

 is to increase the dryness of the air, and, conse- 

 quently, the perspiration of vegetable surfaces. 

 " Evaporation," says Mr. Daniell, " increases in 

 a prodigiously rapid ratio with the velocity of the 

 wind ; and any thing which retards the motion of 

 the latter is very efficacious in diminishing the 

 amount of the former. The same surface which, 

 in a calm state of the air, would exhale 100 parts 

 of moisture, would yield 125 in a moderate breeze, 

 and 150 in a high wind." Hence the great im- 

 portance, in gardens, of walls and screens, which 

 break the wind, and keep the air in repose in 

 their vicinity. The difference between the effect 

 of a given amount of cold upon the blossoms of 

 exposed fruit trees, and those of the same species 

 trained upon walls, is well known ; and appears to 

 be owing to this circumstance much more than to 

 any difference of temperature in the two situa- 

 tions.! 



It is to be remarked that the easterly winds are, 

 in this country, both the coldest and the driest. 



quarters ol the compass, in the proportion of .814 

 to .907, upon an average of the whole year ;" and 

 Mr. Thompson has (bund the hygrometer to indi- 

 cate not uncommonly from 20"^ to 30° of dryness, 

 during the long prevalence of the north-easterly 

 winds in spring. At the same time, the air is 

 very cold, the effect of which is to cause the sap- 

 vessels of the stem to contract, and refuse to con- 

 vey their fluid ; so that the blossoms of fruit trees 

 in a north-east wind, while they are robbed of 

 their fluid contents by evaporation, can get no as- 

 sistance from the roots through the stem, and 

 [necessarily perish. I find, however, from Mr. 

 Thopmson's observations, that the greatest dryness 

 we experience in this climate is not when the 

 wind is in the east, but when it is in the south. 

 For example : in nine years, between 1826 and 

 1834, the four driest days were, in the year 1834, 

 in June, when it was 33^ on the 1st, 35® on the 

 2d, and 31° on the 21st ; on the 1st of June, 1833, 

 it was 30°, and always with a south wind ; and, 

 during the whole of those nine years, there was 

 but one other day on which the dryness was 

 found as high as 30°, namely, on the 10th of 

 April, 1834, with a north-east wind. The dura- 

 tion of dryness with a south wind was, however, 

 very short, not exceeding one or at most two days, 

 and was invariably accompanied with great heat 

 and followed by heavy rain ; while the north- 

 easters last for weeks, without rain and with a 

 comparatively low temperature. The following 

 statement by Mr. Thompson puts this in a clear 

 light. There occurred between 1826 and 1834 

 inclusive, — 



Wind North . . 7 days above 20° of dryness. 



N. East . C 39 do. do. 



East 114 ^48 do. do. 



S. East . ( 27 do. do. 



South . 35 do. do. 



S. West . SO do. do. 



West . 35 do. do. 



N. West . 22 do. do. 



* [The average fall of rain ('and snow) in the 

 state of New York, for 14 years (1826— 1S39 inclu- 

 sive, (as deduced from observations made under the 

 direction of the regents of the University, and col- 

 lected in their Report, presented March, 1840, is 

 34.40 inches. The highest average (from 54 stations) 

 for any single year is 44.40 (A. D. 1827) ; the lowest 

 (-for 1839) 32.10 inches. A. G.] 



t This has been illustrated by Mr. Howard, in the 

 results of some interesting experiments made by him 

 on the annual amount of evaporation. During three 

 years, in which the evaporating gauge was placed for- 

 ty-three feet from the ground, the annual average re- 

 sult was 37.85 inches ; during other three years when 

 the instrument was lower and less exposed, the average 

 was 33.37 inches ; and when the gauge was upon or 

 near the ground, the annual average was only 20.28 

 inches, or little more than half the amount evaporared 

 in a free and elevated exposure. 



These facts sufficiently explain the fatal effects 

 of certain winds upon vegetation, the small com- 

 parative value in this country of walls with north 

 and east aspects, and the general want of success 

 that attends late spring planting. Here, also we 

 in part discover an explanation of the utility of 

 shades interposed between the sun and planta 

 newly committed to the earth ; they not only 

 cut off' the solar rays, but also intercept currents 

 of air, and thus diminish the amount of perspira- 

 tion by two opposite methods. 



As to temperature in the open air, unconnected 

 with atmospherical humidity, there seems to be 

 no means ol regulating or modifying it to any 

 considerable extent. In some respects, however, 

 we have even this powerlul agent under our con- 

 trol ; but, in order to exercise such control, it ia 

 necessary to understand correctly the theory of 

 what is called radiation, which cannot be better 

 explained than in the words of Mr. Daniell. 

 "The power of emitting heat in straight lines 

 in every direction, independently of contact, may 

 be regarded as a property common to all matter; 

 but differing in degree in different kinds of matter. 

 Co-existing with it, in the same degrees, may 



