METEOROLOGY OF 1 897. 
5 
SOIL THERMOMETER. 
§23. Soil temperatures have been taken at dif- 
ferent depths by thermometers with stems extending 
from the surface to the depth whose temperature 
is wanted. The thermometers, of the type shown in 
Figure lo, are of the pattern made by H. J. Green, 
Brooklyn, N. Y., protected by a wooden covering, 
which partly prevents the action of the temperature 
of the intermediate soil. 
SUNSHINE RECORDER. 
§24. The amount of sunshine is recorded by the 
Pickering sunshine recorder. This consists of two 
semi-cylinders— -one for afternoons, and one for fore- 
noons. They are essentially pin-hole cameras. 
The hole is in the flat surface and the image of the 
sun is cast on the curved side of the cylinder oppo- 
site, which is covered with a sheet of photographic 
paper sensitive to the light. We have added wires 
whose shadow indicates the noon hour. The face of 
the cylinder is moved a notch daily, bringing the 
trace of the sun’s rays on a fresh surface of the 
paper. As long as the sun shines it makes a line, 
in which there is a break whenever clouds obscure 
the sun. Hence the record, after being fixed by a 
bath so as to be no longer acted on by light, consists 
of a series of broken lines, one line across the paper 
for each day, the extent of sunshine being shown by 
the lines, the amount of cloudiness by the breaks. 
Fig. 10. The lines can then be measured and converted 
into hours and minutes, bhe sunshine near sunset and sun- 
rise does not record for about half an hour, this is counted 
in our figures according to the character of the day. 
EXPLANATION OF THE TABLES. 
§25. A dry bulb temperature is that of the ordinary 
thermometer. This observation is made at 7 a. m. and 7 p. 
m. The instrument is placed in an instrumental shelter to 
shield it from wind and from radiation from the ground 
and outside objects. The wet bulb reading is that of a 
thermometer with the bulb covered with fine muslin and wet in 
water. The cooling caused by evaporation lowers the 
temperature of this thermometer below that of the similar 
dry bulb. This reading is sometimes spoken of as the 
