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XIX. On a Cycle of Eighteen Years in the Mean Annual Height of the Barometer 
in the Climate of London, and on a constant variation of the Barometrical Mean 
according to the Moon's Declination. By Luke Howard, Esq., F.R.S. 
Received February 4, — Read March 11,. 1841. 
X HAVE already treated this subject, partially and in detail, in the e Climate of 
London*.’ The further and full development of it in that way will be found an under- 
taking more of labour than of difficulty, the materials being already provided for doing 
this through a lunar cycle of eighteen years ; but I am enabled, by means of these, 
to present to the Royal Society some general results, which will prove interesting, 
and probably important to the science to which they belong. 
The like method has been adopted in this paper as in my two former, read before 
the Society, on the connexion of the barometric variation with the Lunar Phases and 
Apsides. I have excluded, by appropriate averages, those effects of the lunar in- 
fluence which belong not to the subject immediately before us. These, however, will 
require, whensoever we may think it time to form a theory, to be examined conjointly 
with the present and every other of the elements of this intricate subject. 
Table I. 
Barometrical Averages on successive Solar Years, from 1815 to 1832, constructed to 
show the Moon’s influence on the Mean Heights, varying according to her Decli- 
nation : for the manner of forming which, see the remainder of this paper. 
Year. 
Days’ ob- 
servations. 
Annual 
mean. 
Moon in or 
near the 
equator. 
Moon at or near 
her greatest 
north declination. 
Moon in or 
near the 
equator. 
Moon at or near 
her greatest 
south declination. 
Averages 
on nine 
years. 
in. 
in. 
in. 
in. 
in. 
in. 
1815 
370 
29-766 
29-8391 
29-7819 
29-7947 
29-8880 
1816 
368 
29-648 
29-7883 
29-7128 
29-7046 
29-8357 
1817 
362 
29-733 
29-7908 
29-8590 
29-8420 
29-7499 
1818 
369 
29-826 
29-8116 
29-8649 
29-8363 
29-8348 
1819 
361 
29-831 
29-7930 
29-8168 
29-9287 
29-7106 
1820 
369 
29-839 
29-8014 
29-8020 
29-9363 
29-8622 
1821 
362 
29-805 
29-8206 
29-9085 
29-7880 
29-7044 
1822 
362 
29-889 
29-8543 
29-8472 
29-9354 
29-9426 
1823 
369 
29-763 
29-8040 
29-8436 
29-6741 
29-7203 
1824 
368 
29-878 
29-9788 
29-9126 
29-9129 
29-7546 
29-8111 
1825 
362 
29-987 
30-0823 
30-0285 
29-8932 
29-9933 
29-8235 
1826 
369 
30-033 
30-0899 
30-0213 
29-9959 
29-9910 
29-8501 
1827 
362 
29’938 
29-9374 
29-8875 
29-9218 
29-9829 
29-8723 
1828 
363 
29-814 
29-8590 
29-7832 
29-7990 
29-8608 
29-8848 
1829 
363 
29-688 
29-6838 
29-6563 
29-6857 
29-7002 
29-8829 
1830 
368 
29-671 
29-7404 
29-6902 
29-6604 
29-6900 
29-8661 
1831 
362 
29-653 
29-6351 
29-6310 
29-6700 
29-5968 
29-8512 
1832 
363 
29-702 
29-6480 
29-8210 
29-7293 
29-6830 
29-8250 
The 
averages on successive periods of 
nine years in the last column exhibit the barome- 
trical mean, increasing and decreasing, as follows : — 29' 8 111 + 0124 + 0266 + 0222 + 0125 
= 29-8848 — 0019 — 0168 — 0149 — 0262 = 29-8250 inch. Then, to complete the cycle, 
29-8250 — 0139 = 29 8111 inch. 
* Vol. i. p. 172. 2nd Edition. 
2 o 2 
