126 
tion, and by the aid of additional funds given by the New York 
Botanical Garden an effort was made to devise an instrument that 
would make such a record. The investigation was intrusted to 
the author, and he was so fortunate as to enlist the interest and 
secure the coéperation of Dr. Wm. Hallock, professor of physics 
in Columbia University, who undertook to devise a thermograph 
that would make a continuous record of the ae ee of the 
soil at any depth desired. A paper by Prof. W. H. Bristol, 
“A new Recording Thermometer for closed sae read before 
the Association at the Brooklyn meeting in 1894, furnished the 
Hallock thermograph. A, bulb containing kerosene. B, hea tube, 
at £, on expansion chamber and fastened to short lever arm at FG, lever extend- 
A, t er in making corrections, and calibrations. 
cylinder driven by internal clockwork which makes one revolution per week. The 
ylinder carries paper ruled horizontally to degrees centigrade e rate.of move- 
ment carries aper pa: at h hours is taken to pass over 
the interval between two curved lines. Z, upright rod on hinged base to remove pen 
from contact with paper. AZ, base of cast iron 
principle upon which the new instrument, which will be desig- 
nated as the Hallock thermograph, was constructed. 
The essential features of the Hallock thermograph are as 
follows: The thermal element of the instrument consists of a cop- 
per bulb or globe 11 cm. in diameter with a strengthening equato- 
