METEOROLOGY. 
“ As tlie sine of the sun’s mean altitude in 
April is to the mean heat of April, so is the 
sine of the sun’s mean altitude in May to 
the mean heat of May. In the same man- 
ner the mean heats of June, July, and 
August, are found ; but the rule would give 
the temperature of the succeeding months 
too low, because it does not take in the 
heat derived from the earth, which possesses 
a degr ee of heat, near ly equal to the mean 
annual tenrperature. The real tempera- 
ture of these months, therefore, must be 
looked upou as arr arithmetical mean 
between the astronomical and terrestrial 
heats. Thus in latitrrde 51°, the astr’orro- 
mical heat of the month of September is 
44.6°, and the mean annual heat is 52.4°; 
therefore the real heat of this month should 
After many laboriorrs calculations Mr. 
Kirw'an had the mortification to find their 
results differed so much from observations, 
that he \^as induced to make a /table from 
various sea joiiruals, and certain prirtciples 
for the monthly mean temperatrrre of tire 
standard, from lat. 80° to lat. 10°, from 
which he decides that the coldest month in 
every latitude is January, and that July is 
the Warmest in all- above 48°, in lower 
August. In proportion to the distances 
from the equator is the increase and de- 
crease of heat, but every latitude where 
existence can bo maintained has a mean 
of 60°, two months of the year at the least, 
which is requisite for the production of 
those articles by which man supports life. 
Tile temperatures within ten degrees of the 
poles vary little, and the case is similar 
within the same distance from the equator ; 
those of different years near the latter 
differ very little, but the differences in- 
crease as the latitudes approach the poles. 
It is well known that the temperature of 
the atmosphere diminishes gradually in pro- 
portion to its height above the level of the 
sea. Tlie late Dr. Hutton of Edinburgh 
made some experiments on this head by 
placing a thermometer on the summit of 
Arthur’s Seat, a hill so named, and another 
at the base of it, by which he found that 
the former generally stood at three degrees 
lower than the latter, in this instance there- 
fore a height estimated at 800 feet pro- 
duced a diminution of heat amounting to 
three degrees. Bouguer made .a similar 
experiment to ascertain the difference of 
temperature between the level of the sea 
and the top of Pinchinca, one of the Andes, 
when the thermometer at the summit stood 
at 30° and that belovv in the same latitude 
at 84°; the diminution was 54° in a sup- 
posed height of 15,564 feet. Thus far the 
operation is easy and practicable, but the 
grand difficulty lies in deterraing the exact 
gradations between the highest and lowest 
points of observation, conjectures on this 
subject have been hazarded by Euler and 
Saiissure, the first gives it in harmonic pro- 
gression, and Saussure supposed tlie de- 
crease of temperature to amount to 1° for 
287 feet of ascent. Mr. Kirwan, however, 
rejecting those improbabilities, shews in the 
Transactions of the Royal Irish Academy, 
that the rate of diminution depends upon 
the precise temperature of the surface of 
the earth where an experiment is made ; 
he has besides invented an ingenious mode 
of ascertaining the rate in every instance, 
admitting the temperature at the surface 
to be known. 
This gradual approach to cold, demon- 
strates that at a certain height eternal con- 
gelation must prevail; that height varies 
of course according to the latitude of the 
place, being highest at the equator, and 
gradually descending on approaching the 
poles ; it is also lower in the winter. The 
cold on the summit of Pinchinca was found, 
by M. Bouguer, to extend from seven to 
nine degrees every morning previous to the 
rising of the sun below the freezing point, 
from which he conjectured, that tlie mean 
height of the term of congelation (or that 
region where water congeals on some part 
of every day in the year) between the 
tropics, is 15,577 feet above the level of the 
sea ; in latitude 28°, he supposes it to be 
13,440 during summer; taking “ tlie differ- 
ence between the freezing point and the 
equator, it plainly appears, that it bears the 
same proportion to the term of congelation 
at the equator that the difference between 
the mean temperature of any other degree 
of latitude, and the freezing point, bears 
to the term of congelation in that latitude." 
“ Thus,” continues Dr. Thomson, “ the 
mean heat of the equator being 84°, tlie 
difference between it and 32 is 52; the 
mean heat of latitude 28° is 72.3°, the dif- 
ference between which and 32 is 40.3. 
Then 52 : 15,577 : : 40.3: 12072.” Mr. 
Kirwan calculated another table on th.is 
subject, from latitude 0, where he makes 
the mean height of the term of congelation 
15,577, by gradations of five degrees, up to 
latitude 80—120 feet ; higher tlian tins, call- 
