REPORT ON METEOROLOGY. 
213 
the following equation for reducing the mean of the tempera¬ 
tures at 10 a.m. and p.m. to the daily mean at any part of the 
year: 
v — \ (ocf+x e) —0'33 -f 0*41 sin £(/* — 1) 30° + 124° 8' 
where v is the mean temperature ; \ (xf -f- x e) the mean of the 
morning and evening temperatures at 10 ; and n the number of 
the month, reckoning from January (= 1). This is intended to 
apply all over Europe *. M. PoggendorfF inquires with some 
justice, whether it would not be better to avoid all calculation 
by inclosing the thermometer in a difficultly conducting medium, 
by which the daily variations of temperature might be dimi¬ 
nished. 
A mechanical mode of taking the mean of an infinite number 
of temperatures has been proposed by M. Grassman, by ob¬ 
serving the change of rate caused by the influence of tempera¬ 
ture upon the uncompensated pendulum of a clock f. The 
idea is a good one, but was proposed long ago by Dr. Brew¬ 
ster J. 
M. Bouvard’s valuable paper upon the meteorological obser¬ 
vations at the Observatory of Paris contains much information, 
deduced from the registers of many years, upon the form of 
the annual curve of mean temperature at Paris He observes 
that the days of greatest and least temperature in the year are 
the 14th January and the 15th July, differing only a day from 
an accurate interval of six months : and each follows the corre¬ 
sponding solstice at an interval of twenty-five days. Baron 
Humboldt has observed the remarkable symmetry of the curve 
on either side of its maximum ordinate ||. The same author has 
pointed out the near coincidence of the days of mean tempera¬ 
ture observed, even in the too short continuance of registers 
which we possess If; these are 
Buda, 18th April and 20th October. 
Milan, 13th- and 21st - 
Paris, 22nd-and 20th- 
These interesting inquiries lead to the general subject of 
Climatology, which, since the publication of Humboldt’s mas¬ 
terly Essay on Isothermal Lines**, has assumed a more satis- 
* PoggendovfF’s Annalen, 1825. 'f Ibid. 
X Edinburgh Encyclopedia, Art. Atmospherical Clock. 
§ Memoires de VInstitut pour 1824. M. Bouvard has also given an equation 
for the diurnal curve depending upon the sine of the angle corresponding to 
the time from noon. 
[| Fragments Asiatiques , ii. 422. Ibid. p. 426. 
* * Memoires d’Arcuetl, tom. iii. p. 462—603. 
