36 REPORT—1858. 
through air, and afterwards solidified in a vacuum. The author adds some theo- 
retical considerations in explanation of the formation of hail. 
Further Evidence of Lunar Influence on Temperature. 
By J. Park Harrison, M.A. 
In illustration of the effects of lunar influence, the author adduced proofs of the 
frequent recurrence of high and low temperatures on the same day of the moon’s 
age, and also at shorter lunar intervals, not only at Greenwich and Dublin, but at 
Madras, Toronto, and the Cape of Good Hope. He also expressed his belief that 
the fall in temperature which takes place at full moon, before first quarter, and 
shortly after last quarter*, is due to the clearing of the atmosphere at those periods, 
and the higher temperature about the period of new moon and first quarter to a 
more clouded state of the sky, the effects observed being attributed to the action of 
terrestrial radiation. In a subsequent communication attention was drawn to the 
very different degree of heat which the moon’s crust attains at first and last quarters ; 
and to the general clearness of the sky at the periods of greatest fall in temperature 
in the months of January and May. 
On the Decrease of Temperature over Elevated Ground. 
By Professor Hennessy, RS. 
The author showed that the decrease of temperature in ascending through the 
atmosphere depended not only on height above the sea-level, but also upon the abso- 
lute height above the nearest surface of solid land. As the temperature of the air 
at any point depends not only on the pressure at that point, but also on the amount 
of heat which may be transferred thither by circulation and radiation, it must be a 
function of the several elements upon which these calorific influences depend. It 
must therefore vary with the distance of the point from heating or cooling surfaces, 
as well as with its height above the sea. It will also depend upon the time of the 
day, and even on the season of the year, for the energy of the causes referred to is 
manifestly subjected to periodical variations depending upon the position of the sun. 
The increuse of temperature observed in ascending for short distances above the 
ground during the night, and even sometimes during the dayt, will thus have its 
anomalous character explained. In this way the decrease of temperature over plains, 
mountains, and plateaux would be necessarily very different; and we cannot imme- 
diately infer the state of the phenomena in the two latter instances from what may 
exist in the former. Some of the results of observations made on the hills and 
mountains of Ireland during the Ordnance Survey, as contained in the volume recently 
published by Col. James, were referred to as illustrations of these general views. 
On the Heating of the Atmosphere by Contact with the Earth's Surface. 
By Professor Hennessy, F.RS. 
The temperature of the atmosphere depends principally on the heat which the earth 
receives from the sun, and on what it loses by radiation. A portion of the solar heat 
is absorbed in passing through the air, while another portion penetrates to the earth’s 
surface. The ground becomes thus heated, and the lower strata of the atmosphere 
acquire the greater part of their heat from contact with the warmed surface. It is 
admitted that the mode in which the air becomes heated by contact with the ground 
must be a kind of circulation analogous to that seen in the movements of a heated 
mass of liquid, such as boiling water. When studying the vertical movements of 
the atmosphere, with reference to which Prof. Hennessy had made a communication 
to the Association last year, he had been led to consider the connexion between such 
movements and the influence of the heated ground. In order to study the ques- 
tion experimentally, thermometers were suspended at different heights above the 
ground, and under different circumstances of exposure to the influence of the sup- 
* See Report for 1857, p. 249. 
+ See Prof. Forbes in Reports of the British Association for 1840, p. 60. 
