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1910] BRIEFER ARTICLES 217 
of the whole system consisting of A and its attached parts. In the initial 
position, as shown in the figures, the center of gravity is not only higher 
than F, but also at some distance to the left of a perpendicular through 
F. A considerable amount of mercury must therefore pass into 0’ 
before the center of gravity will have shifted to the right of the perpen- 
dicular sufficiently to tilt the beam. The tilting of the beam carries 
the center of gravity yet farther to the right, and the beam therefore 
rests in the new position until the reverse movement of the mercury has 
carried the center of gravity to its former position in the beam. It is 
evident that if the center of gravity be raised yet higher above F, it will 
also be farther to the left when in the first position, and a larger volume 
—— =ji=— |) 
FIG. 3 
of water will have to be displaced from 6’ by mercury before the beam 
will tilt. Each record, therefore, will indicate a larger amount of water. 
Advantage is taken of the relation between the center of gravity and 
the center of suspension to calibrate the instrument. A weight is placed 
upon the bar £, and by sliding it up or down the bar or exchanging it for 
another, the center of gravity is adjusted at will. The point of suspen- 
sion may also be moved. 
The atmograph, set up as shown in the photograph (fig. 4), recorded 
the passage of to cc. units. By lowering the weight, the quantity could 
be reduced by half, or set at any intervening amount. Experience 
indicates that under ordinary conditions ro cc. will be a convenient unit 
for field work with Lrvincston atmometers. 
Standard copper pipe and fittings are used throughout, no rubber 
being employed excepting for the flexible connection c’. Electrical con- 
nections are made from one of the binding posts shown in the photo- 
Staph to the pipe e, and from the other to the flange f. The circuit is 
closed through the stopcock while f is in contact with the handle. A 
single dry cell is employed as the source of current. 
