Extremes and means of soil temperatures for 1889, etc.--Continued. Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec. 3-inch depth: Maximum. Minimum 6-inch depth: Maximum. Minimum 24-inch depth: Maximum. Minimum 48-inch depth: Maximum Minimum 35.5 61.0 76.5 68.5 79.5 89.0 92.0 98.0 92.5 92.5 82.5 68.5 65.0 70.5 57.5 48.0 37.0 37.5 52.5 57.0 58.5 67.0 76.5 80.0 86.0 77.0 82.0 89.5 74.0 65.5 60.0 62.5 52.0 50.0 53.5 53.0 56.5 63.0 71.5 75.0 79.5 79.0 84.5 74.5 69.0 60.5 67.0 58.0 56.5 59.5 56.5 56.0 60.5 62.5 69.0 73.0 73.5 76.5 74.5 70.0 65.0 62.0 60.5 67.0 69.0 80.5 92.5 95.0 101.0 96.0 96.0 84.5 71.5 69.5 34.0 58.5 65.0 66.5 79.5 88.0 91.0 97.5 93.0 92.0 82.0 69.0 SOIL TEMPERATURES OBSERVED AT PENDLETON, OREG. Among the United States experiment stations for which soil temperatures have been published, I quote the following observations made by Mr. P. Zahner, voluntary observer at Pendleton, Oreg., (lat. 45°.7 N.; long. 112°.2 W.; altitude, 1,122 feet), because it represents a climate so different from that found in the same latitude east of the Rocky Mountains. A number of observations of diurnal periodicity are given by Zahner, and a shorter series is at hand for Corvallis, Oreg. (lat. 44°.5 N.; altitude, 150 feet). The comparison between these shows that the Pendleton air and soil are appreciably warmer than the Corvallis in July, August, and September, but colder in November and probably also in December. In general the maximum soil temperature at Pendleton at all depths follows that of the daily maximum air temperature. Rainfall lowers the temperature of the soil, as on March 18, 1890, at 8 inches depth by 2° F., but at 24 inches depth by 0.5° F. At 12 inches depth the soil was not frozen throughout the year, but at 8 inches it was frozen up to the 7th of March. The soil temperatures were read daily at 3 p. m.; the soil was naturally dry and light, and was covered with a thin grass. The thermometers were maximums and minimums, apparently read from above ground without being disturbed in their positions. Observations at Pendleton, Oreg., in 1890. [From the Monthly Reports of the Oregon State Weather Bureau.] Precipitation. Total monthly rainfall.. Soil temperature. 4-inch depth: al. 19 a1.52 a2.04 0.17 a1.51 a1.80 a0.08 0.07 a0.27 a0.63 0.01 SOIL TEMPERATURES OBSERVED AT MONTREAL, CANADA. As illustrating temperatures of the ground in a very cold locality, I quote the work of Messrs. C. H. McLeod and D. P. Penhallow, of McGill College Observatory, Montreal, who have maintained a series of observations of the temperature of the earth by Becquerel's method, in which the temperature of a coil of wire in the laboratory is brought to equality with the temperature of a similar coil buried in the earth. The following table gives the mean temperature for the tenday periods ending on the dates given in column 1 and at a depth of 1 foot below the surface of the ground. Temperatures are given by them for other depths, as also for the air; the total rain and snow is also given. An investigation of the connection between earth temperature and the development of vegetation is being carried on by them, but as no results have as yet been published I give merely their soil temperatures at a depth of 1 foot, which usually agree, within a degree centigrade, with the average temperature of the air for ten days. Mean temperature of the soil at a depth of 1 foot for periods of ten days at Montreal, Canada. This series seems to show the powerful influence of a snow covering to keep the ground from cooling to very low temperatures during the winter. The minimum temperatures at 1 foot depth were --0.5° F. during the twenty days March 22 to April 10, 1889, and +0.4° F. during the ten days March 17 to 26, 1890. METHODS OF MEASURING SOIL TEMPERATURE. As it is very important that there should be numerous observations of soil temperature available for agricultural study, and as many persons are deterred by the expensiveness of the deep-earth thermometers, I would call attention to the fact that agriculture does not need to consider temperatures at depths below 4 feet. Several methods of measuring deep-earth temperatures have been most thoroughly studied in the memoirs of Wild and Leyst of St. Petersburg, a summary of which I have prepared and will submit at another time. For accuracy and convenience nothing can exceed the thermophone devised by Henry E. Warren and George C. Whipple, of the Massachusetts Institute of Technology. The soil thermometers constructed in accordance with suggestions made by Milton Whitney, of the South Carolina Experiment Station have been used by him at several stations and he has published a description of this new self-registering soil thermometer as follows (see Agr. Sci., Vol. I, p. 253; Vol. III, p. 261): This is a modification of Six's form of thermometer in which the maximum and minimum temperatures are registered in one and the same instrument. The essential features of the thermometers are as follows: A cylindrical bulb 6 inches long, filled with alcohol. The bulb is protected by a somewhat larger cylindrical metal tube, containing numerous holes, and is to be placed 3 inches below the surface of the soil-i. e., so that the bulb will extend vertically between the depths 3 and 9 inches, respectively, in the soil. The tube carrying the alcohol extends some 6 or 8 inches above the surface of the ground, when it bends twice at right angles and descends again to the surface, bends at right angles twice, crossing the main stem, and is carried up about 6 or 8 inches again, where it terminates in a bulb partially filled with alcohol. The lower bend in this stem carries a column of mercury which is drawn back toward the bulb when the alcohol contracts, and pushes a steel index up to the minimum temperature on a scale which reads downward. This index is held supported in the alcohol by a little spring when the alcohol expands and the mercury leaves it, while another index is pushed up to the maximum temperature by the other end of the column of mercury. The indices are set by the help of a magnet. The advantages claimed for this instrument are that it gives at once, without any calculation, the mean temperature of a definite depth of soil, for which we now use at least three thermometers, while it gives in addition the maximum and minimum temperatures, and need only be read once a day instead of three times, as at present. * * * Thermometers can be made, of course, with bulbs longer or shorter than the one described. We adopted the length of 6 inches placed 3 inches below the surface, as in our experience that represents a layer of soil in which most of the roots of the cotton plants are contained. We expect to distribute a number of these instruments through the * * * State [South Carolina] and have records kept for us near signal-service stations in our typical soils- -a method which could hardly have been arranged with the old form. The great trouble about the instrument is the danger in transportation of having the index get down in the mercury column. For this reason it has to be transported in a box on gimbals to swing freely within a larger box, so that it will always remain upright. We had such a box made, capable of carrying eight or ten instruments. From experiments at Houghton Farm (Agr. Sci., Vol. II, p. 50) F. E. Emory finds that the thermoelectric couple and galvanometer, as used by Becquerel, consumed much time and was frequently useless owing to atmospheric electricity and ground currents. Short-stem graduated thermometers, with bulbs immersed in oil and fastened at the lower end of a light wooden rod, gave good results when the temperature at the thermometer was not warmer than that of the overlying soil or the atmosphere; otherwise a circulation of air takes place. He finds that the telethermometer, giving a continuous record, answers his needs, but we know nothing of its accuracy. T. C. Mendenhall (1885) describes a modified form of thermometer for observing the temperature of the soil at any depth, which he calls the “differential resistance thermometer." Experiments with this instrument at Washington, D. C., have shown him that it is much less troublesome than Becquerel's electric method, but still too troublesome to be recommended to any but persons accustomed to electric measurements. Mendenhall's arrangement consists essentially in utilizing the varying resistance of a platinum wire which extends from the upper end of an ordinary mercurial thermometer down into its bulb. The total resistance diminishes as the temperature rises and allows the current to flow through less platinum but more mercury. The changes in the resistance are measured by the galvanometer, but he hopes to substitute for this the telephone, which will make the apparatus more convenient for general use. [It is desirable that Mendenhall's method, or Becquerel's, or the thermophone be provided in connection with the ordinary buried longstem thermometers in order that by an annual or more frequent set of comparative observations the changes in the zero point of ordinary thermometers may be detected.—C. A.] |