492 
Nothing but a long series, of simulta- 
neous observations, mude with great at- 
tention by persons in various parts of 
the Kingdom, and. subsequently: com-: 
pated and collated, can be of much 
avail in caleulating the probability. of 
any peculiar state of the weather at any 
given period. And even deductions of 
this nature ‘are liable to be disturbed, 
however accurately they may be made, 
by unforeseen changes and inscrutable 
modifications: 
That.a mere change of temperature 
is the immediate agent (or parent) of 
many of the atmospherical phenomena, 
has’ been long known to every person 
who is moderately conversant with me- 
teorological inquiries: but the modus 
operandi’ of this agent has not been so 
clearly’ defined as might have been 
wished.’ Some’ believing the agency of 
heat-or cold to be only plus or minus of 
the same substance, and simply operating 
by mechanical agency ; whilst others 
allow a certain’ degree of chemical 
agency to the operations of heat or 
cold; ‘as’ either of these extremes pre- 
vail in-our atmospheric medium. 
That the quantity of aqueous vapour 
held. in solution by the atmosphere 
bears a certain degree of relation to the 
temperature of the air at any given pe- 
riod, is so well known, as to render it 
unnecessary to offer any exemplification. 
But with respect to the influence of the 
hygrometrie state of the atmosphere upon 
the minimum temperature of the night, 
a Mr. Anderson, of Perth, has lately 
made a communication to the Edinburgh 
Philosophical Journal, from which I 
shall beg leave to offer a few extracts. 
This gentleman claims the honour of 
having first pointed out to the public 
this coincidence between the state of- 
moisture and the minimum tempera- 
ture, some years back, in the Edinburgh 
Encyclopedia. Without disputing this 
claim (though some little doubt exists 
on the subject), I shall render him the 
justice, which the sagacity of his present 
remarks entitle him to, by giving his 
own words : 
“ In the case of the daily change of tem- 
perature, there is some interval between the 
maximum and the minimum condition, 
which may be regarded as the temperature 
belonging to the season of the year; and 
though that point is not, at all times, 
equally distant from the extremes between 
which. it oscillates, it seldom departs far 
from. their mean.point, If this mean were 
to rise.and sink regularly, as the. year ad- 
yanced and declined, without. being subject 
to daily fluctuation, the quantity of moisture 
On Meteorological Inquiries. 
(Jan.1, 
_ existing. in, the atmosphere, at) any given 
time, might be determined bye the ‘therma-. 
meter alone, with considerable p CISION, AS. 
it would generally be less than the. uantity 
corresponding to the mean ua and 
seldom greater than’ that Which bélongs to 
the minimum temperature’; the’ latter set- 
ting limits: to the ‘acctmiulation’ of (watery 
vapour in the'atmosphere y while the'former 
no less effectually secures it against a state 
of long-continued dryness. -|,The) truth: of 
these assertions will be readily, perceived, 
by a comparison of; the .minimum, tempera- 
ture with the point of deposition, jor, the 
temperature at, which the moisture existing 
in the atmosphere would begin to deposit 
itself.” "4 
Mr. Anderson then proceeds:to, shew, 
that the quantity of, humidity) inthe 
air, from along series of observations, 
and taking the mean ‘temperature: of 
each separate month, follows inyariably. 
the order of the temperature: and that 
the coincidence between )the,, minimum 
temperature. of the night, and the point 
of condensation, of aqueous vapours 
at all times sufficiently nearto (warrant 
the conclusion, that they are dependent 
on each other; thewariation between the 
point of deposition and the lowest tempe- 
ralure of the night not exceeding 1° 
Farenheit, taking the .average.of the 
twelve months. ; “pee 
Mr. Anderson estimates the quantity 
of atmospheric vapour, in the, summer 
months, at somewhat more than double 
that of the winter months; being, on 
an average of the whole year, 1814 
grains in 100 cubic inches of air. It is 
also obvious, that during the autuninal 
months, the atmosphere is more highly 
charged with vapour than during the 
opposite months of the spring, owing to 
the sun’s influence on evaporation durin 
the summer months. The usual au- 
tumnal rains, therefore, may be con- 
sidered only as a condensation of the 
excess of vapour raised by the high 
temperature of the summer quarter.” — 
Mr. Anderson next proceeds, to. exa- 
mine the phenomena which result from 
the conversion of, water. into;,vapour, 
and vice versa, as a corroboration of his 
views with regard to the coincidence of 
the point of condensation and the mi- 
nimum temperature. AF OF HONIRG 
Mr. A. satisfactorily | shews, ‘that 
although the reduction of temperature 
uniformly lessens the capacity of com- 
mon air for aqueous vapour, yet at a. 
certain point (which is that: of deposit 
‘of the vapour), a reaction takes. place; 
the vapour, as. it. becomes ‘condensed 
into the liquid state, giving'off.a consi= 
: derable 
