RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 37 
in determining the character and influence of surface temperatures, 
the telethermoscope offers great possibilities. 
The soil thermograph is desirable for continuous records of soil 
temperature which can hardly be obtained with any other instru- 
ment, and particularly for measuring the extremes, which it is almost 
impossible to obtain with registering thermometers. These can be 
had only after careful adjustment of the range of the pen, or by fre- 
quent checking against a thermometer, at high and low temperatures, 
after the instrument is installed. This instrument should at least 
be employed wherever new stations are being established, and until 
the daily curve has been worked out for each season. The securing 
of a record with this instrument is very similar in its routine fea- 
tures to the work with air thermographs. There is. however, one 
feature of the soil thermograph which deserves special consideration. 
This is the tendency, whenever the instrument is moved and the con- 
necting tube suffers more or less deformation, for the whole appa- 
ratus to go through a gradual readjustment. One frequently finds 
the pen steadily ascending or descending for a week after any chang r e. 
For this reason it does not appear practicable to calibrate or adjust 
the recording apparatus to agree with an accurate thermometer be- 
fore placing the instrument and its bulb in their final positions. The 
Ecological Society, in outlining methods for a systematic soil tem- 
perature survey, however, recommended calibrating soil termographs 
by placing the bulb in a pan of water with the thermometer, and after 
placing the bulb in its final position in the soil trusting completely 
to the accuracy of the thermograph. 
It is believed, in view of what has been said, to be absolutely 
necessary to have a thermometer so placed in a wooden or porcelain 
tube that its bulb is at the same level and practically in contact with 
the bulb of the themograph, and to obtain frequent comparisons of 
the thermograph and thermometer. 
Special Suggestions ox Surface Measurements. 
It has been stated that the extremely high temperatures attained at 
the surface of a well-insolated soil seem to have an important bear- 
ing on the initiation of plants, and that technical difficulties make the 
actual measurement of this surface temperature almost impossible. 
Doubtless this could be accomplished from time to time with \ super- 
sentive plate such as constitutes a part of the leaf-temperature appa- 
ratus, but the problem of recording the maximum attained in a day 
or a season would still be unsolved. 
It should be admitted, therefore, that a record of the maximum 
temperature at the soil's surface can only be approximated with 
present equipment, for the very simple reason that the object which 
