Amount evaporated, in inches and hundredths, from the soil. First Day. Second Day. Third Day. Fourth Day. Fifth Day. Sixth Day. Seventh Day.

The amount of evaporation from water, at the same time, was, First Day. Second Day. Third Day. Fourth Day. Fifth Day. Sixth Day. Seventh Day. .59 .53 .47 .43

.45

.46

.37

This shows how rapidly evaporation takes place from the surface after a rain, more than a fourth of the whole amount of moisture in the soil being raised the first day. As soon as the earth becomes dry, the evaporation is scarcely appreciable. At the end of the second day, at the temperature given above, the earth will generally have become dry to the depth of from .07 to .11 in.; and after eight days, plants which do not penetrate the soil more than four inches will begin to suffer from drought, and require watering. In the higher temperatures which we frequently have, evaporation is more rapid. But if a light rain falls on a hard surface, it cannot penetrate to any great depth; while, on a light and porous soil, it is absorbed at once, and will not evaporate so rapidly, since it is in some measure protected by the earth. So with dews. We have seen that on a hard surface there is no dew, or but little; and even if there were much, it would very soon evaporate; while on a mellow, porous surface, much more is deposited, for the reason intimated above, and it must remain longer in the soil. It is a curious fact, also, that the most thoroughly drained land stands the drought best. This is explained by the consideration that the roots of plants can shoot down to a greater depth in such land without finding substances injurious to them.

Now, our summer rains ordinarily come at considerable intervals, and are immediately followed by scorching suns or drying winds. Still more frequently they come in showers, followed by an atmosphere as clear and unclouded as any in the world. If the rain has penetrated through a light, porous soil, it may evaporate sooner than the same amount of moisture distributed through the same depth of a hard and impermeable surface; but we have seen that the same amount of rain does not penetrate the hard surface, or, if at all, only to a partial extent,

10

and its evaporation consequently is as rapid as that from the porous surface, or even more so.

There can be no greater mistake than to fear to injure the crops by the evaporation gained by mellowing the soil. Plants never suffer so much as when the surface becomes a little hard and forms a thin crust, which cuts off all communication with the air. But when this crust is broken, and the earth is loosened, the dews reach the roots of plants, and are often sufficient to support vegetation a long time without rain. Let any one who doubts try the experiment, and he will be convinced of the advantage of deep ploughing and frequent loosening of the soil. I am the more anxious to recommend this practice of frequently stirring the surface of cultivated lands, because by means of the cultivator for the larger crops, like Indian corn and potatoes, and the onion weeder, that indispensable labor-saving machine for root crops, it may be done by every farmer with very little expense.

The question has frequently been raised, whether our climate has undergone any perceptible change within the last two hundred years, or since the settlement of the country. The subject was so well treated in a communication to the Board of Agriculture by the Hon. John C. Gray, and published in the Report of last year, that I shall only briefly allude to the present state of the question. Statistics give no good evidence of any material change; but nothing is more common than to hear the remark, that our winters are not so severe, or that we never have such severe storms, as formerly, while our summers every year become more oppressive; or, in other words, that the climate is warmer than it was. We can hardly believe that an impression which prevails so generally can be entirely without foundation. Besides this, we know that causes have long been in operation which tend to produce the effect in question. These causes have incidentally been alluded to above, and need not be dwelt upon here any further than to say, what has already been intimated, that dense forests must prevent the snow from melting and the moisture from evaporating within their limits, and thus lower the temperature of the atmosphere within them, making, as it were, a reservoir of cold air, from which a constant current will be poured upon the surrounding country. In

the same way, they must protect the sources of our springs and running streams, so that their destruction must increase the liability to drought in the whole adjacent region. The last effect has probably been produced in the manner indicated, whatever may be our conclusion on the general question of climate; and I think most men can call to mind streams which are much smaller now than formerly, rivers that have dwindled almost to brooks, brooks that have become little rills, and rills that no longer exist. The same process is going on upon the continent of Europe, and many of the large rivers there have become perceptibly smaller, and probably from the same causes, since it is pretty conclusively shown that the amount of rain, so far from having diminished, has slightly increased since the year 1689, when the positive data as to the quantity of rain at Paris begin. The same slight increase has also probably taken place at Milan. Accurate observations were made on the Oder from 1778 to 1835, and on the Elbe from 1728 to 1836, which establish a very considerable progressive diminution of water, and from which it appears that, if the diminution continues in the same ratio as since 1781, it will be necessary, after 1860, to change the form of vessels used on the Elbe, and to construct those of less draught. The decrease there is ascribed to the causes specified above, and chiefly to the clearing up of forests, the draining of ponds and marshes, and the reclaiming of swamps.

We have seen that no accurate records were kept in the early history of the colony, indeed, that there were no means of keeping any till the middle of the last century. The diaries, both manuscript and published, which have been consulted, give some information on this subject, though it is more general and less to the point than could be desired. We learn from them that there were many winters when it was common to pass with men and teams to and from the islands in Boston Harbor, Shirley Point, and across the river to Charlestown. We find, too, that not unfrequently the snows were very deep and the roads impassable. But all deductions from such vague accounts as those are unreliable, when compared with those drawn from careful registers of the weather.

On the other hand, we may infer that our climate has not

greatly changed within the last hundred years, from an examination of the following table of the mean temperature of the summer months at Cambridge, near Boston, during the period from 1742 to 1774, and that of the same months, from 1793 to 1812, and from 1841 to 1852, inclusive :

These figures show a most striking resemblance between the periods in question, and certainly give no color to the idea that our summers have become any warmer.

It is proper, in this connection, to notice very briefly the difference between the climate of England and our own. This subject also was so ably treated in the paper above referred to that it will not be necessary to dwell upon it at any length here. I desire only to show how little we can rely upon the results of experiments made in England, and how unsafe it would be for us to follow implicitly, in every case, the precepts of British agriculturists.

The climate of England is proverbially damp, with almost constant cloudiness and rain; hence the greenness and verdure of its fields, which are never parched up like our own. The soil of any country, of course, will be moist or dry according as its atmosphere is moist or dry. As the summer advances, and the heat increases, both will gradually lose their moisture; and the degree of dryness will be in some proportion to the intensity and long continuance of the heat. Hence, as the temperature never rises so high in England as with us, and never continues at its highest point there as here, the English farmer will never suffer from the droughts which oppress us.

The average number of days on which it rains in England during the year is no less than 178.1, giving a monthly aver age of nearly fifteen days. In other words, it rains in England, on an average, almost every other day. The following tables give the average number of days on which it rains near Lon

don for each of the several months during the ten years, 1807-1816, and during the period between 1817 and 1823:—

But the average number of days per month on which some rain or snow fell at Salem, near Boston, during the same years, (1807-1823,) was as follows, including even the slightest

Or, to take a longer term of years, and, therefore, a more accurate standard of comparison, we have the average number of days on which some rain or snow fell at Salem, from 1786 to 1828, as follows: