Part 29 (1/2)
[149] _Memoria sui Boschi di Lombardia_, p. 45.
[150] _economie Rurale_, i, p. 22.
[151] ROSSMa.s.sLER, _Der Wald_, p. 158.
[152] Ibid., p. 160.
[153] The low temperature of air and soil at which, in the frigid zone, as well as in warmer lat.i.tudes under special circ.u.mstances, the processes of vegetation go on, seems to necessitate the supposition that all the manifestations of vegetable life are attended with an evolution of heat. In the United States, it is common to protect ice, in icehouses, by a covering of straw, which naturally sometimes contains kernels of grain. These often sprout, and even throw out roots and leaves to a considerable length, in a temperature very little above the freezing point. Three or four years since, I saw a lump of very clear and apparently solid ice, about eight inches long by six thick, on which a kernel of grain had sprouted in an icehouse, and sent half a dozen or more very slender roots into the pores of the ice and through the whole length of the lump. The young plant must have thrown out a considerable quant.i.ty of heat; for though the ice was, as I have said, otherwise solid, the pores through which the roots pa.s.sed were enlarged to perhaps double the diameter of the fibres, but still not so much as to prevent the retention of water in them by capillary attraction. See _App._ 24.
[154] BECQUEREL, _Des Climats, etc._, pp. 139-141.
[155] Dr. Williams made some observations on this subject in 1789, and in 1791, but they generally belonged to the warmer months, and I do not know that any extensive series of comparisons between the temperature of the ground in the woods and the fields has been attempted in America.
Dr. Williams's thermometer was sunk to the depth of ten inches, and gave the following results:
+-------------+--------------+--------------+-------------+
Temperature
Temperature
TIME.
of ground in
of ground in
Difference.
pasture.
woods.
+-------------+--------------+--------------+-------------+
May 23
52
46
6
” 28
57
48
9
June 15
64
51
13
” 27
62
51
11
July 16
62
51
11
” 30
65
55
10
Aug. 15
68
58
10
” 31
59
55
4
Sept. 15
59
55
4
Oct. 1
59
55
4
” 15
49
49
0
Nov. 1
43
43
0
” 16
43
43
0
+-------------+--------------+--------------+-------------+
On the 14th of January, 1791, in a winter remarkable for its extreme severity, he found the ground, on a plain open field where the snow had been blown away, frozen to the depth of three feet and five inches; in the woods where the snow was three feet deep, and where the soil had frozen to the depth of six inches before the snow fell, the thermometer, at six inches below the surface of the ground, stood at 39. In consequence of the covering of the snow, therefore, the previously frozen ground had been thawed and raised to seven degrees above the freezing point.--WILLIAMS'S _Vermont_, i, p. 74.
Bodies of fresh water, so large as not to be sensibly affected by local influences of narrow reach or short duration, would afford climatic indications well worthy of special observation. Lake Champlain, which forms the boundary between the States of New York and Vermont, presents very favorable conditions for this purpose. This lake, which drains a basin of about 6,000 square miles, covers an area, excluding its islands, of about 500 square miles. It extends from lat. 43 30' to 45 20', in very nearly a meridian line, has a mean width of four and a half miles, with an extreme breadth, excluding bays almost land-locked, of thirteen miles. Its mean depth is not well known. It is, however, 400 feet deep in some places, and from 100 to 200 in many, and has few shoals or flats. The climate is of such severity that it rarely fails to freeze completely over, and to be safely crossed upon the ice, with heavy teams, for several weeks every winter. THOMPSON (_Vermont_, p. 14, and Appendix, p. 9) gives the following table of the times of the complete closing and opening of the ice, opposite Burlington, about the centre of the lake, and where it is ten miles wide.
+------+-------------+------------+-------+
Year.
Closing.
Opening.
Days
closed.
+------+-------------+------------+-------+
1816
February 9
1817
January 29
April 16
78
1818
February 2
April 15
72
1819
March 4
April 17
44
1820
{February 3
February
} 4
{March 8
March 12
}
1821
January 15
April 21
95
1822
January 24
March 30
75
1823
February 7
April 5
57
1824
January 22
February 11
20
1825
February 9
1826
February 1
March 24
51
1827
January 21
March 31
68
1828
not closed
1829