The use of mercury in the stem of the thermometer not only admits of the use of the index for registering the maximum temperature, but possesses the additional advantage of reducing the error due to uncertain temperature of the stem to about one-sixth what it would be if alcohol were used. Moreover, if necessary, as in the case with thermometers for greater depths than that figured, the ungraduated portion of the stem can be made of very much finer bore than the graduated portion, the effect of which is to diminish the objectionable error to a comparatively unimportant quantity. The chief objection to thermometers of this construction is the liability of alcohol getting from the bulb into the stem during the processes of construction, graduation and subsequent handling, and the difficulty of safely shipping them. When once set up, however, there seems to be little or no possibility of derangement and the error common to mercurial thermometers due to rise of the freezing point with age does not apply owing to the high coefficient of expansion of the alcohol used in the bulb. APPLICATIONS OF SOIL THERMOMETRY. =116. Estimation of the Absorption of Heat by Soils.=—A cubical zinc box, six centimeters square, is filled with the sifted air dried soil. The box, one side of which is left open, is encased snugly in a wooden cover, exposing only the open end, and placed for a few hours in the direct rays of the sun. The temperature is then taken at a given depth. The box may be provided with thermometers at different depths, the bulbs thereof extending to the center. In this case the box should be covered with thick felt instead of wood. The temperature of the layers of soils of different depths can thus be read off directly. The air temperature directly above the box should be accurately noted while the experiment continues. Any other kind of box well protected against all heat save the direct sunlight on the open surface of the soil will answer as well as the one described. To determine the action of moist earth in similar conditions the soil may be previously moistened; the per cent of moisture being determined in a separate portion of the soil or the amount of water added to the air-dried soil being noted. =117. Estimation of the Conductivity of Soils for Heat.=—The bulb of a thermometer is placed in the middle of a mass of fine earth which is then exposed, best in a metallic box painted with lamp black, in a warm place. The time required for the thermometer to reach a certain degree is noted. By reversing the experiment and placing the mass of earth heated to a given degree in a cool place the conductivity can be determined by the time required for the mercury in the thermometer to fall to any given point.