TRANSACTIONS OF THE SECTIONS. 4l 
as well as the relative humidity of the atmosphere, together with the 
dew-point, might be obtained. He concluded his observations on the 
subject by pointing out the exact coincidence which holds between the 
dew-point and the minimum nocturnal temperature; and proved that 
the quantity of moisture in the state of vapour, which exists in the air 
in every region of the earth, operates as a check upon the diminution 
of temperature by radiation during the night; for this obvious reason, 
that the transition of the aqueous vapour to the liquid state evolving 
its latent caloric, warms the cireumambient air, and by giving birth, at 
the same time, to clouds in the form of vesicular vapour, counteracts 
the cooling processes to which the nocturnal air is exposed in the ab- 
sence of the sun. This fact, so important in meteorology, affords an 
illustration of the reason why the windward sides of continents and 
large islands are warmer than their leeward sides, in the same parallel 
of latitude; and why dry and parched tracts of land are always found 
liable to severe cold during the night. It also furnishes an explanation 
of the causes which occasion the deflections of the isothermal lines, 
when taken in connexion with the modifications which these lines re- 
ceive from geographical position and elevation above the earth’s surface, 
On a Method of Prognosticating the probable mean Temperature of the 
several Winter Months from that of corresponding Months in the 
preceding Summer. By Grauam Hurcuinsoy, Esq. 
From the slowness with which the increased temperature of summer 
penetrates the surface of the ground, it occurred to the author, that 
the last portion absorbed during the summer half of the year, and 
which descends to the least depth below the surface, should be the 
first portion given off during the winter half; and in like manner, that 
the first portion absorbed during the summer half, and which must 
descend to a greater depth below the surface than any other portion, 
should be the last to be given off during the winter half; and agreeably 
to the principle above stated, the months in which an absorption of heat 
takes place, should have corresponding months of retrocession, or some 
approximation thereto; and consequently that the mean atmospheric 
temperature of any month in the summer half of the year, would afford 
a means of prognosticating the mean temperature of its corresponding 
’ month in the winter half, so far at least as that mean atmospheric tem- 
perature depended upon the retrocession of heat absorbed during the 
“previous summer half. The corresponding months of temperature 
assumed by the author, are as follows :— 
August has October following 
yaly me ee for its corresponding month 
May A January of temperature. 
April .. February 
If, then, August be warmer than its average, the mean atmospheric 
