PHILOSOPHICAL TRANSACTIONS. 
XX. On the Barometrical Variation as affected hy the Moons Decimation. 
By Luke Howard, Esq., F.R.S. 
Received January 16, — Read June 19, 1845. 
These calculations were begun with the year 1815, and continued to 1832: the 
present paper continues them to 1841. The method used to bring out the averages 
may be thus described. Beginning as nearly as may be at the winter solstice, the 
days of a solar year are classed in what may be termed weeks of declination, mostly 
of seven days each, the middle day of each week corresponding, — 1, with the moon’s 
position coming north from the equator ; 2, with her position in full north declina- 
tion ; 3, with her position returning to south over the equator ; 4, with her full south 
declination. The average, or mean height of the barometer, in each of these classes, 
is presumed to express the relative power, or effect, of the position to which it be- 
longs ; when divested of the much larger amount of variation due to the effect of a 
northerly or southerly current, of the variable pressure of the aqueous atmosphere, 
of the temperature of the season, the deposition of rain, &c. Mixed with these, the 
weekly averages offer a mass of results sufficiently discordant ; but the discrepancy 
vanishes when those under each class are averaged upon the solar year ; the other 
movements now balancing and neutralising each other. 
The present series of averages extends then from December 20, 1832, where the 
former ends, to December 23, 1841. It corresponds nearly with the latter or cold 
half of the cycle of annual temperatures, which I have already laid before the public. 
And it being probable that a close connexion exists between the pressure and the 
temperature of the atmosphere of these latitudes, in its variations, my taking these 
limits may facilitate to students a careful comparison of the two, throughout a cycle. 
In my paper of March 1841, the mean height of the barometer for each of the four 
positions came out, by averages upon eighteen years ending with 1832, as follows, viz. — 
Moon coming north over equator 29 - 8724 in. 
Moon in north declination 29’8608 in. 
Moon going over equator, south 298450 in. 
Moon in south declination 29‘8261 in. 
3 M 
MDCCCXLVI. 
