- for the Year 1821. _ 275 
Evaporation. Inches. 
Greatest monthly quantity in June sgn, Saeed 
Least monthly quantity in January 16 0:41 
Total amount for. the year .. an oe. 21°86 
Rain, &c. Inches. 
Greatest monthly quantity in December .. 7°61 
Least monthly quantity in February »» O18 
Total amount for the year oe ee 43-4] 
N. B.—The barometer is hung up in the Observatory fifty 
feet above low-water mark ; and the self-registering horizontal 
day and night thermometer, and De Luc’s whalebone hygro- 
meter, are placed in open-worked cases, in a northern aspeet, 
out of the rays of the sun, ten feet above the garden ground. 
The pluviameter and evaporator have respectively the same square 
area: the former is emptied every morning at 8 A.M., after rain, 
into a cylindrical glass gauge accurately graduated to 1-100dth 
of an inch; and the quantity lost by evaporation from the lat- 
ter, is ascertained at least every third day, and sometimes oftener, 
when great evaporations happen .by means of a high tempera- 
ture, and dry northerly or easterly winds. 
BaRoMETRICAL PressuRE.—lIn the course of the year the 
mercurial column has met with an unprecedented range, having 
risen higher and sunk lower than we ever saw it before. Its 
greatest elevation occurred in February, which was characterized 
by fair and frosty weather, and was the coldest month in the 
year; and its greatest depression happened at midnight of the 
24th of December, a remarkably wet and windy month. (See 
rain column in the table, and the London Magazine for February 
_ 1822 for the remarks made at the time.) The range between 
the annual extremes is 2°72 inches. The year having been wet, 
particularly the last four months, and the elasticity of the at- 
mosphere much disturbed by prevailing gales of wind, the an- 
nual mean pressure, therefore, is also unprecedented, being 
1-20th of an inch lower than that of last year, and rather more 
than 1-20th of an inch lower than the mean for the last seven 
years. ' 
The aggregate of the spaces described by the mercury in its 
alternate rising and falling is 8-86 inches more than that of the 
preceding year, and the number of changes five more. ‘ 
For 170 days of this year while the moon was in North de- 
clination, the mean pressure was 1-8th of an inch higher than 
that in the 153 days in which she ranged in South declination. 
Last year the mean pressure was greatest while she was in South 
declination, and vice versé the year before. 
M m 2 TEM- 
