in a small shallow pan of about the same size. The pan
with its turf, after being carefully weighed, was put out on the lawn in
the place where the turf had been cut. It was exposed for some hours
while dew was forming, and on these occasions it was always found to lose
weight. It was thus evident that vapor was rising from the ground while
dew was forming, and therefore the dew found on the grass was formed of
part of the rising vapor, trapped or held back by coming into contact
with the cold blades of grass.

The difference between these experiments, in which the exposed bodies
_lose_ weight, and the well-known ones in which bodies are exposed to
radiation, and the amount of dew formed is estimated by the _increase_ in
their weight, is pointed out. In the former case, the bodies are in good
heat-communication with the ground, whereas in the latter little or no
heat is received by conduction from the earth.

Another method employed for determining whether the conditions found in
nature were favorable for dew rising from the ground on dewy nights was
by observations of the temperatures indicated by two thermometers, one
placed on the surface of the grass and the other under the surface, among
the stems, but on the top of the soil. The difference in the readings of
these two thermometers on dewy nights was found to be very considerable.
From 10 deg. to 18 deg. F. was frequently observed. A minimum thermometer placed
on, and another under, the grass showed that during the whole night a
considerable difference was always maintained. As a result of this
difference of temperature, it is evident that vapor will rise from the
hotter soil underneath into the colder air above, and some of it will be
trapped by coming into contact with the cold grass.

While the experiments were being conducted on grass land, parallel
observations were made on bare soil. Over soil the inverted traps
collected more dew inside them than those over grass. A small area of
soil was spread over a shallow pan, and after being weighed was exposed
at the place where the soil had been taken out, to see if bare soil as
well as grass lost weight during dewy nights. The result was that on all
nights on which the tests were made the soil lost weight, and lost very
nearly the same amount as the grass-land.

Another method employed of testing whether vapor is rising from bare
soil, or is being condensed upon it, consisted in placing on the soil,
and in good c