1850. 



THE GENESEE FARMER. 



m il 



This capacity to hold immense quantities of water 

 imbibed from the orean, lakes, rivers, the foliage of 

 trees, and moist earth, in a volatile condition, to be 

 distributed over broad coritinents, is a wonderful pro- 

 vision of nature. But the filling of the air with 

 water, like a wet sponge, is less remarkable tlian the 

 contrivance for squeezing the sponge, so to speak, and 

 causing the diffused moisture to fall in gentle rains, 

 snows, and dews. The dr;/ing of the atmosphere, 

 after it is saturated with water, is a phenomenon 

 witliout which it would never rain ; nor could there 

 be any springs, rivers, land plants, or animals on the 

 globe. This precipitation of water is etTected by a 

 change of temperature, which change is the result 

 of llie revolution of the earth on its axis, and of solar 

 heat. Day and night, spring, summer, autumn, and 

 winter, with their ever-varying temperature, varying 

 winds, and clouds, and constantly changing humidity, 

 are all results of fixed laws, which invite the research 

 of every reasoning mind. 



Solar HeaT. — According to Professor Forbes, 

 the rays of heat coming from the sun and passing 

 througe tlie atmosphere in the shortest line, at the 

 latitude of Paris, lose 25 per cent, of their calorific 

 power by the lime they reach the earth. Rays that 

 strike tile atmosphere at an angle of only 25°, part 

 with half their intensity, or heat, by the time they 

 touch the ground. The molecules of air absorb and 

 radiate heat into space, the same as other ponderable 

 bodies. Hence, no matter how clear the atmosphere, 

 neither the rising nor the setting sun imparts so 

 much light or heat to those parts of the earth so 

 affected, as they receive when the sun is at the 

 meridian. The effect of solar rays on the earth is 

 still further diminished morning and evening, by the 

 fact that fewer fall on any given area, because they 

 impinge upon its surface obliquely. One can look 

 at the setting sun with impunity, not because it emits 

 less heat or light at that time, but because the rays 

 are mostly absorbed and radiated in passing through 

 many miles of atmosphere before they reach the eye 

 of the observer. 



Tlie facility with which solar heat penetrates and 

 warms the soil to the depth of six, twelve, eighteen, 

 and twenty-four inches, and the radiation of heat 

 from the earth, the leaves of plants, and all other 

 substances, deserve particular notice. 



A distinction must be made between the radiation 

 of heat from the surface of any body, and the trans- 

 mission of it through any substance, as iron, wood, 

 water, mold, or soil. All these hold different rela- 

 tions to this peculiar element. It is not intended to 

 take more than a popular view of this subject. At 

 the time of seeding in spring, a single day is suffi- 

 cient to warm to the depth of four inches, a mellow 

 soil recently plowed. Two days of sun will warm 

 the ground six inches, and six days twelve inches. 

 The fall of warm rain on a well-drained, mellow soil, 

 greatly hastens the heating of the earth. On the 

 contrary, the fall of a cold rain, or much cold water 

 in the ground, greatly retards the rise of temperature 

 in tilled land. Heat and water should be studied 

 together, if one would obtain a clear idea of their 

 joint influence on vegetation. When water evapo- 

 rates, it expands to 1,696 times its former volume, 

 and renders latent, or insensible, a considerable 

 amount of active heat. Hence, a wet piece of 

 ground, from the surface of wliich a good deal of 

 water evaporates, is always cooled by the constant 



loss of sensible heat which rises in vapor and departs 

 far into the atmosphere. 



The warmer the atmosplicre, the greater is its 

 capacity to hold water in the condition of a diffused, 

 invisible vapor. The lower strata of air are heated 

 much more by caloric radiated from the earth than 

 by the absorption of heat from the sun in its passage 

 to the planet. Air thus heated becomes expanded or 

 rarified, and specifically lighter than the colder air 

 above it. This causes the air within and near the 

 tropics to rise high above the surface of the earth, 

 and flow over botli north and south, toward either 

 pole, while colder and heavier air rushes in toward 

 the equator to fill the empty space. These aerial 

 currents are deflected in their courses by the diurnal 

 revolution of the earth, and by mountain ranges 

 whose summits are often covered with eternal snow : 

 and they are still further modified by the varying 

 temperature of the ocean and its peculiar streams. 



Heat and water are the fruitful parents of winds 

 and clouds. When aqueous vapor is precipitated in 

 rain or snow, heat that was latent becomes again 

 sensible, and by increasing the capacity of the air to 

 hold water in the form of vapor, prevents a disastrous 

 deluge of this abundant element in nature. The 

 laws which restrain the precipitation of water from 

 the clouds are no less curious than those which cause 

 it to rain at all. The atmosphere must approach 

 saturation before it can rain : and it usually happens 

 that the quanties which will fall on a given area, one 

 hundred feet above the ground, and on the earth, are 

 unequal. Large drops, in falling through many feet 

 of dry air, become smaller by constant evaporation, 

 and may he wliolly dissipated before they reach the 

 earth. On the other hand, quite small drops formed 

 in cold regions, higli in the air, constantly condense 

 more vapor in falling through a saturated atmosphere, 

 and will be many times larger when they reach the 

 ground than at their starting point. 



To illustrate the production of rain, let us suppose 

 that a current of air at 70^ temperature, saturated 

 with moisture, meets and mingles with another cur- 

 rent, also saturated, but having a heat of 50°. Now, 

 if the atmosphere at the mean temperature of 60° had 

 a capacity to hold water as an invisible vapor, equal 

 to the mean of 70° and 50°, it is obvious that no pre- 

 cipitation would take place. But such is not the fact. 

 The quantity of water held in air heated from 60° to 

 70° can not be contained in that heated from 50° to 

 60°. In other words, whatever cools air saturated 

 with moisture, causes a cloud, dew, mist, or rain. 



Early and late frosts are produced by the radiation 

 of heat, during clear nights, from the foliage of plants 

 and other terrestrial bodies. If the temperature of 

 the air is not very low at sundown, and is humid, 

 vegetation will so soon reach the deiv-poiiit, that the 

 latent heat, evolved by the formation of much dew, 

 will prevent a frost. If the atmosphere is dry, clear, 

 and still, the dew-point is lower, and all the circum- 

 stances are favorable to freeze the little vapor con- 

 densed on such substances as radiate heat with the 

 greatest facility. Any thing which checks the radi- 

 ation of heat, like a cloud, smoke-screen, or wind 

 which agitates the atmosphere, serves to prevent 

 frost. E\'ery farmer should have a thermometer and 

 rain-gauge, and know the degi'ee of heat most favor- 

 able to all his crops. The dew temperature and 

 moisture of the soil are as much elements of produc- 

 tion and profit, as good manure and skillful tillage. 

 The writer has studied the growth of corn in differ- 



