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COMPARATIVE METEOROLOGICAL OBSERVATIONS. 



A, in tbo accompanying figure. This vessel is filled with earth taken from near the 

 place where the observations are to be made. The depth from the surface to the 



Lysimeter. 



Lamout'a Atmometer. 



false bottom is that at which the observation is pro- 

 posed to be made. The lower bottom is funuel- 

 ehaped, and is connected with a leaden pipe, through 

 ■which the water flows into a receiving vessel (D.), 

 for measuring, from time to time. To accomplish 

 this, a pit is dug, 10 feet long, 6 feet wide, and 5 

 feet deep, and into this the discharge-pipes from the 

 instruments, at several depths, are brought. Such 

 an instrument is called a Lysimeter. If the surfaces 

 of some of these are covered with moss, leaves, humus, 

 turf, &c., while others are left with bare earth, the 

 influence of these coverings upon the percolation of 

 water may be determined. This instrument should 

 at first have the surface of the earth within it a little 

 higher than the ground, so as to allow settling, and. 

 it should be left some months undisturbed before 

 beginning observations, so as to allow the contents 

 to get compacted, as occurs naturally in the soil. 

 From this we get data for learning the amount of 

 water that penetrates the soil and reaches springs. 

 If we deduct the amount collected from the rain- 

 fall, we get the amount evaporated, lost, or absorbed 

 by vegetation. 



4. The evaporation meter (atmometer) determines the daily and yearly amount 

 of water returned to the air by evaporation. Comparisons of the amount of evapora- 

 tion and of rain-fall will show, in certain 

 localities, that more water is evaporated 

 than falls in rain, &c. The instruments 

 should be freely exposed to the winds, 

 but should be sheltered from rains, 

 snows, and the direct rays of the sun. 

 Lament's atmometer, shown in the an- 

 nexed engraving, consists of three prin- 

 cipal parts, a water-reservoir, a, h, c, d, 

 an evaporating-bowl,/, g, h, and a con- 

 necting tube. It R. A piston, passing 

 through an air-tight packing, is so 

 arranged that it may be pressed down 

 into the reservoir or raised by the 

 screw S, and an index, ii, attached to 

 this, points to the degrees on a gradu- 

 ated scale, s 8. This scale may be raised 

 or lowered, so that its zero point is oppo- 

 site the index point n, when the instru- 

 ment is set at the beginning of an observ- 

 ation. The mode of operation and of 

 reading are as follows: The piston is 

 drawn up, and rain-water is poured in 

 at the bowl till it stands at the point 

 A. The reservoir being full of water, 

 the scale is set so that the index points 

 to zero, and the i^iston is then pressed 

 down, so that the water in the bowl is 

 forced up so as to stand level with a line 

 M. N. marked on the inner side just 

 below the rim. When an observation is 

 made, some time after, the piston is 

 raised and all the water in the bowl is 



drawn in until it stands just level with the opening A. If there had been no loss, the 

 index would then point at zero ; but, as more or less evaporation has taken place, the 

 ditference is at once shown by the index on the scale. More water is added, if neces- 

 sary, the scale is again set, and the water pressed up to the mark near the rim of the 

 bowl, as before, and left till next observation. The bowl having a much greater sec- 

 tional area than the reservoir, the graduation of the scale is enlarged in corresponding 

 degree, as compared with the depth actually evaporated if measured in the bowl 

 itself. The scales used were graduated to tenths of Paris lines, and the reading by 

 estimation could be had for smaller distances. 



The instrument is placed upon a stand about 5^ feet above the ground, freely exposed 



