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from them. It remains now to speak of the cause of droughts, and the means of guarding against them.
There can be no doubt, as already intimated, that the de. struction of our forests has much increased the severity of our summer droughts, and this effect may have been produced without any actual change in our mean annual temperature. All. growing vegetables, and dense forests in particular, have a tendency to lower the temperature of the earth, by the large amount of evaporation which constantly takes place from their leaves, and by protecting the ground against the burning rays of the summer sun. It is a fact well known to every farmer, that deep snows lie much longer in thick forests than in the adjoining open plains. It is also well established by direct experiment, that the temperature of the soil, at the depth of twelve inches, in a forest, in the summer, is no less than ten de. grees lower than at the same depth in an open field adjoining.
The forests, moreover, play a much more prominent part in producing rains than most persons, at first sight, would suppose. This is particularly the case when they stand on hills and elevated ground; in such situations their influence frequently extends to a considerable distance. The sources of rivers are found in them; they also determine the direction of the prevailing winds, and consequently the rains; hence the importance of protecting the forests which stand on land higher than the surrounding country.
These are, it is true, but general considerations; but as they explain, to some extent at least, the increase in the frequency and severity of droughts, which must be apparent from the sketch before given, I shall venture to extend them so far as to give place to the remarks of a late eminent French writer, whose statements show that the same causes have operated in the south of France, which is subject to droughts somewhat like our own. The land,” says he, “in most parts of France, stripped of the forests which once covered it, now presents a bare surface, which the clouds sweep over without finding any obstacles to arrest their progress and resolve them into rain. The soil, exposed to the rays of a scorching sun, is penetrated to a great depth, the sources of streams have dried up, and the rivers scarcely fill a third of their
channels during the summer. Moreover, the winds, having no longer to blow over those immense forests, under the shade of which they were refreshed, and where they were impregnated during the dry weather with a warm moisture which they spread over the country, no longer bear with them freshness and life; forced, on the other hand, to blow over large extents of country parched by the sun, they become hot, and bear with them heat and sterility. Consider what North America was on the arrival of the Europeans. The soil, covered with dense forests throughout nearly its whole extent, offered to its occupants only frosts and snows for half the year; but the Europeans changed this state of things; the draining of stagnant waters, and, still more, the clearing of woods, which they effected soon after their settlement, were not long in diminishing the abundance of rains, and consequently drying the soil and rendering it warmer. Now, the Americans enjoy the advantages of their labor and industry; but let them take care not to pass the line of demarcation, which indicates the quantity of wood to be preserved, in order to have always the quantity of water necessary to the fertility of the soil; let them take care, especially, not to touch those grand forests, which, by their position, are in the way to arrest the clouds."
The grand old forests of Massachusetts have, unfortunately, long since been “ touched;" and if they had not, the arm of the government even could hardly protect them from the hands of individual proprietors at the present prices of wood. The remedy for this evil would be, as the writer just quoted suggests, to form new plantations of wood in elevated places from which it has been cut, and to increase it in others where there seems not to be enough of it to produce the effect desired. In some locations, it would be a source of profit to the individual and the public to plant a large part of the poor soil with forest trees. It is, however, a well-established fact, that the forests of this State are at the present moment actually increasing in extent, though most of them are of a young growth. *
Professor Espy, whose Philosophy of Storms has given him * A reference to my last Annual Report will show the manner of forming plantations of pines.
a wide reputation as a meteorologist, suggests that droughts may be caused by the irregular burning of fallows or large tracts of wood or prairie land in summer, and that man, by his ignorance, may be the cause of them. “ The summer rains at present are local, and of very limited extent; and though they travel towards the east, like winter storms, they are not extensive enough to cover the whole country in their progress; hence, portions of the country are liable to be parched with drought and hot weather. May it not be possible that this irregularity is in part produced by the irregular burning of fallows and prairies, thus producing partial and irregular rains, interrupting the wide-extended and general rains which would otherwise take place as they do in winter ?"
It is well known that the clouds which produce rain are com. posed of vapor, created by an evaporation from the surface of the earth, and from water, which takes place while the sun shines by day, and is, for the most part, suspended when the dew falls by night.
This vapor remains in the air until it is condensed into water by a low temperature of the atmosphere, and then ordinarily falls in rain. After it has thus fallen, the whole process of evaporation or creation of vapor, formation of clouds, and condensation of the vapor into water, must be again gone through with before there can be more rain. This, in summer, generally requires some time; hence, immediately after a rain in any given place, the air in that region is not likely to be in such a state as is favorable to the production of rain.
The winds greatly hasten the process of evaporation, while the clouds and the absence of the sun hinder or stop it altogether. An increase of temperature, also, usually causes a great increase of evaporation from the surface of the earth. In the proverbially moist climate of England, where the amount of evaporation must be far less than in our own, it is sometimes equal to six inches a month; that is, to an amount of vapor which, if condensed into water, would make six inches. In our climate, of course, it must be much greater.'
If, now, from some local cause, there is a shower of rain, the moisture of the atmosphere, being collected and condensed, moves on in the form of clouds till these clouds no longer find
sufficient vapor in the air to support them. If, just after this local rain, a general storm begins, or one which might, under other circumstances, have been general, it moves on till it arrives at the place of the former rain. But this previous rain has already exhausted the surplus of moisture which the air at that place contained, and the second storm must come to an end; whereas, if there had been no local rain in this first place, there would have been sufficient moisture to enable the general storm to continue on its course. On the other hand, if a general rain occurs, extending over a large space of country, and moving, as it does, from west to east, local rains cannot ordinarily take place within the same space for six or seven days, on account of the scarcity of vapor in the air.
Now, on these general laws, Professor Espy has founded a curious and ingenious theory for the production of artificial rains, which shall be general, extending all over the country in times of drought. These, of course, would render the practi. cable precautions which I shall have the honor to suggest of comparatively little importance. I will give his theory in his own words :
“Now, if masses of timber, to the amount of forty acres for every twenty miles, were prepared and fired simultaneously every seven days in the summer, on the west of the United States, in a line of six or seven hundred miles long from north to south, then it appears highly probable from the theory, though not certain until the experiments are made, that a rain of great length, north and south, would commence on or near the line of fires; that this rain would travel towards the east, side foremost; that it would not break up until it reaches far into the Atlantic Ocean; that it would rain over the whole country east of the place of beginning; that it would rain only a few hours at any one place; that it would not rain again until the lower air becomes charged with vapor, and the upper air has radiated off the heat which it received during the rain, from the evolution of the latent caloric of the vapor, condensed in the formation of cloud, which effects could hardly be produced in less than a week; that it would rain enough, and not too much, in any one place; that it would not be attended with violent wind, either on land or on the Atlantic Ocean; that there would be no hail nor tornado at the time of the rain, nor intermediate; that there would be no destructive floods nor injuriously low waters; that there would be no oppressively hot nor injuriously cold weather; that the farmers and mariners would always know, in advance, when the rains would commence, or nearly so, and when they would terminate; that all epidemic diseases originating from floods and droughts would cease; that the proceeds of agriculture would be greatly increased, and the health and happiness of the citizens much promoted.”
As it is not probable that an appropriation will be made sufficient to secure the success of the experiment, or that the inhabitants of Berkshire will burn over their mountains for the sake of watering the eastern parts of the State in dry weather, it will be necessary to confine our attention to somewhat more practicable methods of guarding against the effects of droughts. The importance of adopting them will be apparent to all.
The first and simplest is, to reclaim and cultivate low lands. The amount of swamp lands reclaimed every year in this State is sufficient evidence that both the practicability and the profit of this means are well appreciated. Eminent success has attended every experiment of the kind which has come under my observation; and the statements made to agricultural societies abundantly show that these lands, when properly treated, pay a large percentage of profit, larger, indeed, than any other part of the farm. No encouragement is needed to induce the intelligent farmer to engage in this enterprise. It tells its own story in redoubled crops. The methods of reclaiming are so well stated in the returns made to the Board every year that it would be unnecessary to dwell upon them here, even if it came within the range of this report. It is enough to say that some methods specdily repay all advances made on them, while others require a considerable expenditure, and make no return, or comparatively little, for two or three years. The compound interest which such improvements often pay at the end of that time should, perhaps, satisfy any reasonable expectation; but most men prefer to invest where they can get a speedy dividend.