127 
rial ridge, filled with commercial kerosene. A short section of 
copper tubing with a heavy wall is soldered to an opening in one 
pole of the globe, and the free end of the heavy tube receives a 
small copper tube with an external diameter of about 4 mm., a bore 
of one millimeter, and of any desired length. The tube is also 
filled with petroleum. The free end of the small tube is con- 
nected with a chamber consisting of a pair of corrugated brass 
disks 8 cm. in diameter with the edges soldered together. The 
chamber is seated on a metal block fastened to the base of a re- 
cording apparatus and the tube connects with the chamber 
through an opening in the metal block. An opening is made 
in the upper side of the first chamber and a second chamber of 
the same kind is soldered to it, the interior of the two chambers 
being thus connected (see Fig. 19, D). The pair of corrugated 
chambers are filled with petroleum as convenient during the 
course of construction, and care is taken to exclude all air from 
the bulb, tube and chambers. As the temperature in the bulb 
is made to rise it expands, and as both it and the small tube 
have fairly rigid walls, the total expansion of the liquid is made 
An upright post is fixed to the upper wall of the pair of cham- 
bers, and it may be lengthened or shortened in making the nec- 
essary adjustments. This post connects with a short arm 4 cm. 
in length at F, running to an axis held in bearings between 
two upright standards. A second arm 17 cm. long carrying 
double ruled paper and occupies a weele in a single revolution. 
The instrument is now adjusted so that the pen bears against the 
point on the paper indicative of the same temperature as that of 
the bulb as determined by a mercurial thermometer, and it is 
ready for use. At the end of a week the paper, bearing a con- 
tinuous tracing of the temperature for that time, is removed and 
another put in its place. 
The peculiar usefulness of this apparatus lies in the fact that 
the bulb may be buried in the soil at some distance from the re- 
