A NEW THEORY OF DEW. 629 
that the dew is the result of condensation by the air of warm vapor as it rises 
from the soil. The course of experiments from which this novel scentific theory- 
was deduced is as follows ; 
The basis of the theory is the discovery that in summer the average temper- 
ature of the earth at night is greater than that of the atmosphere. The tempera- 
ture of the earth in an inclosed space on a level with the surrounding soil, and 
the temperature of the air were taken at the warmest time of day and the coldest 
time of night for several months, and the average temperature of the air for the 
season was found to be 72.94°, and that of the soil 72.061°; but the average 
temperature of the air at night was 49.664°, and that of the soil 56.37°, the 
earth thus averaging at night over 6° warmer than the atmosphere. The tem- 
perature of the soil and air at night was also taken at various points within ten 
miles of the college, on all kinds of grass land and bare soil, and in the forest, 
and the same facts were obtained, the soil being at all times warmer at night than 
the air. 
These results led to experiments on dew-fall. Two boxes, each of a cubic 
foot capacity were filled with soil without disarranging its strata, one receiving 
absorbent, retentive loam, and the other peat. These boxes were placed in a 
trench in an open field level with the surrounding ground and exposed to the 
weather. Through the month of June they were weighed night and morning, 
and, unless there was a rain in the night, they uniformly weighed less in the 
morning than at night, the loss being from one to three ounces for the loam and 
one to four ounces for the peat. This Prof. Stockbridge thought indicated that 
the soil at night gave forth water, and that the moisture found on the surface of 
a field in the morning came from a deeper soil rather than from the air. Other 
similar experiments followed. In one a cabbage plant was enclosed in an air- 
tight tin case. Where the stem of the plant protruded through the top of the 
case, wax was used to make it impossible for moisture to escape through the 
leaves. The can was first kept within doors and weighed night and morning, 
when it always showed a loss during the night of from 1.21 grams to 1.78 grams. 
When left out of doors at night, with the can wrapped in cloths to prevent moisture 
reaching it, the loss was from .55 grams to 4.23 grams, showing a loss even 
when there was moisture or dew on the leaves. 
These experiments, continued through the season, gave Prof. Stockbridge 
these proofs of his proposition, that the dew on the ground in the summer is the 
condensation of vapor that rises from the earth, i. The vapor of the soil is 
much warmer at night than the air, and would be condensed by it. 2. Vapor 
from the soil is soon diffused and equalized in the whole atmosphere, but in 
largest proportion when evaporation is taking place near the surface of the soil ; 
and, other things being equal, plants nearest the earth have the most dew. 3. 
Dew under haycocks, boards and like objects on the ground could receive it 
from no other source. — Industrialist. 
