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192 



THE POMOLOGIST AND GARDENER. 



1871 



Iiocal Temperatures — Bearing on Fmlt Cul- 

 ture. 



Bt F. Hawk, Leavenworth, Kan. 



Ed. Pomoloqist and Gardener : Heat or va- 

 ried temperature, and its different effects on diflFer- 

 ent substances, with their varied powers of receiv- 

 ing and transmitting it, affords not only of them- 

 selves vast numbers of curious phenomena, but are 

 the immediate forces in the economy of animated 

 nature itself Leaving the different theories of the 

 chemical nature of caloric to the scientist, we will 

 pass to some of its relations, combinations and 

 practical effects on the affairs of life. 



Among the many sources of latent lieat, the most 

 essential amount and quality necessary to a healthy 

 growth of vegetation, is evidently absorbed directly 

 from the sun. The force or intensity from this 

 source is mainly proportional to the verticity of 

 that planet, modified by a given surface. Of 8,000 

 of the sun's rays that fall perpendicularly, and reach 

 the earth, 7,000 only reach the surface, when they 

 are at an angle of 50 degrees, and when at 40 degrees 

 frost may occur. 



Altitude plays a notable part in the modification 

 of teuiperature.s. Elevation above the level of the 

 ocean or the general level of the country makes a 

 regular variation in temperature ; the first 300 feet 

 makes a difference of a degree, almost as truly as 

 though the height had been measured. This arises 

 from the diminution of reflected heat from sur- 

 rounding objects. After ascending 300 feet the 

 thermometor falls a degree in 295 feet, then at 277, 

 252, 223, and 192 feet ; so that at au elevation of 

 1539 feet the thermometer will fall six degrees. 



While such principles apply in a general way, 

 different results are produced at local situations. 

 For instance : It is known that the destruction of 

 fruit in the germ occurs from frost in our climate 

 wore often on the low grounds and in the valleys 

 than on the uplands. Three causes lead to such re- 

 sults, viz : a limited distribution of the sun's rays; 

 radiation of heat from the surface without refrac- 

 tion, and evaporation. The position of much of 

 the surface of valleys relative to the sun is such as 

 to receive his rays at a small angle, with a conse- 

 quent decrease of the raj's and force. The ground 

 under such conditions is not warmed up to the same 

 degree as that of a comparatively level .surface, such 

 as the uplands that receive the rays more direct. 



At night when this warming process ceases, the sur- 

 face parts with tliis limited heat very readily by ra- 

 diation. Sheltered as it is from the action of the 

 winds, this heat ascends aloft until it reaches the 

 uplands, when it is refracted by the passing breeze, 

 and is thus kept near the surface ; while the cold 

 and heavier air presses down to the lowlands and 

 into the valleys. This produces compound results; 



as while the temperature of the uplands is increased, 

 that of the low grounds and valleys is decreased. 



Evaporation is a force in its results much like that 

 of radiation. Every drop of water or diffused mois- 

 ture that is evaporated from the surface carries with 

 it an equal degree of heat that would be required 

 to convert a drop of water into vapor by artificial 

 means. This invisible vapor is continually arising, 

 and with its heat carried to the uplands. Some- 

 times however it is condensed into fogs that remain 

 in the valleys and lowlands until they are attenua- 

 ted by rarifaction, when they ascend and are dissi- 

 pated. In the spring of the year, when these forces 

 are very active, a sharp line between the tempera- 

 ture of valleys and uplands is often rendered per- 

 ceptible to the senses. 



No general rule can be established that will elu- 

 cidate and apply to these different phenomena in 

 all localities. There are too many contingencies 

 embracing such as the extent and depth of the val- 

 leys, their trend and moisture, slopes, nature of the 

 soil, etc. There may be situations and conditions 

 where the temperature of a portion of a valley may 

 have a higher thermal range at some period of the 

 twenty-four hours, in some seasons of the year. 

 Such localities are peculiarly objectionable; for the 

 great diurnal range that necessarily follows is det- 

 rimental to the health of plants as well as the hu- 

 man system. 



Hence we find that some portions of a valley may 

 be comparatively salubrious, and others are the re- 

 verse. Among the vine clad valleys of Europe, 

 vineyards have become celebrated for the excellence 

 of their wines, while ethers in the same neighbor- 

 hood with different exposures, are of but indiffer- 

 ent quality; the varieties of grapes being the same 

 and no material analytical difference in their soils. 

 The one has perfect climatic conditions, the others 

 not. 



Jf Transpiration of liCavea. 



Von Pettenkofer, in the course of recent research 

 es upon the amount of evaporation which takes 

 place from the foliage of plants, ascertained in the 

 case of an oak tree that this increased gradually 

 from May to July, and then decreased till October. 

 The number of leaves on the tree were estimated at 

 751,600, and the total amount of evaporation in the 

 year at 539 ruble centimeters of water for the whole 

 area of the leaves. As the average rain-fall for the 

 same period was only 65 centimeters, the amount 

 of evaporation is thus eight and a half times greater 

 than that of llic rainfall. This excess must, of 

 course, be drawn up by the roots from a great 

 depth. The inference is derived from the above, 

 that the trees prevent the gradual drying of a cli- 

 mate by restoring to the air the moisture which 

 would otherwise be carried oft' by drainage. 



