472 
A New Theory of Dew, 
i July. 
the converse of this, viz., that dew is the result .of con- 
densation, by the air, of warm vapour as it rises from the 
soil. The course of experiments from which this novel 
scientific theory was deduced is outlined below. 
The basis of the theory is the discovery that in summer 
the average temperature of the earth at night is higher than 
that of the atmosphere. The temperature of the earth in 
an enclosed 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*940°, 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*370°, the earth thus averagingat night over 6° warmer 
than the atmosphere. The temperature of the soil and air 
at night was also taken at various points within 10 miles of 
the college, on all kinds of grass land and bare soil, and in 
the forest, and the same fadts 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 
disturbing its particles or 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 uni- 
formly weighed less in the morning than at night, the loss 
being from 1 to 3 ounces for the loam, and 1 to 4 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 experi- 
ments 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 im- 
possible 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 
1*21 to 1*78 grms. When left out-doors at night, with the 
can wrapped in cloths to prevent moisture reaching it, the 
loss was from 0*55 grm. to 4*23 grms., 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 
