New York Agricultural Experiment Station. 
Ill 
Iii order that such an instrument may be corrected 
to a standard, the amount of surface exposed by the 
terra-cotta must be delicately adjustable. This is 
accomplished by means of the slender brass rod A B, 
which has threads cut upon its upper end, upon 
which work the thumb screws shown at D. The rod 
passes through the cylinder of terra-cotta C, which 
is attached to it by a small brass washer soldered to 
the rod at each end of the cylinder. By turning the 
thumb screws at D, the cylinder is raised or lowered 
at will, and may be fastened securely at any desired 
point. 
As illustrated in the last report, the tube E made 
a return bend at the bottom and the cylinder of terra- 
cotta was inserted directly into the open end. This 
introduced an error, as the expansion and contraction 
of the air in the upper end of the tube due to changes 
in temperature or atmospheric pressure, caused a 
considerable fluctuation in the height of the water in 
the short arm, and consequently the cylinder of terra-cotta was 
unequally supplied with water at different times. In order to avoid 
this error as far as possible, the shallow closed cup E has been sub- 
stituted for the bend in the tube. The diameter of the cup is three 
inches, while that of the tube is but half an inch; hence the slight 
variations in altitude of the water in the tube due to meteorological 
changes exert scarcely a perceptible influence upon the depth of water 
in the cup. A third change consists in the addition of the slender 
tube G, which forms a connection between the air above the water in 
the cup, and the external air, thus insuring access of the latter at all 
times to the cup. This access might become wholly or in part 
obstructed by the soil, if the only communication between the cup and 
the external air were by the orifice through which the terra-cotta 
passes into the cup. 
This instrument is designed to be placed in the soil in autumn, in 
order that the earth may become compact about it in a natural man- 
ner; or it may perhaps be inserted at any other time by making the 
hole just large enough to receive it, and then partially filling this hole 
with puddled earth in order to secure complete contact of the soil 
with the terra-cotta. 
It is proposed to adjust the instrument to a standard in the air, as it 
would be difficult or impossible to do this in the soil. 
