46 
LIEUT.-COLONEL SABINE ON THE LUNAR 
seventeen months thus examined, that a maximum of pressure corresponds to the 
moon’s passage over both the inferior and superior meridians, being slightly greater 
in the latter case ; and that a minimum corresponds nearly to the rising and setting, 
or to + 6 h . The average of the seventeen months gives the respective pressures as 
follows, viz. — 
in. 
Moon on the meridian . . . . 28 - 2714 
Moon in the horizon .... 282675 
The difference being ‘0039 in. 
“ The latitude of the observatory is — 15° 57 ' ; the height above the sea, ascertained 
by levelling, 1764 feet to the cistern of the barometer. Observations made in 1827 
under the direction of Major-General Walker, gave the particulars of the oceanic 
tides as follows : — 
Rise at new moon 
Rise at full moon . 
Rise at the quarters 
Establishment . . 
. . 3 feet 6 in. 
. . 2 feet in 
. . 1 foot 5 in. 
. . 2 h , 20 m . 
“There appears to be no establishment in the atmospheric tide, consequently the 
rise in the ocean will not account for the variation in the height of the barometer, 
because the times of maximum do not coincide.” 
Early in 1842 Captain Lefroy was succeeded in the charge of the observatory at 
St. Helena by Captain Smythe of the Royal Artillery; and from the 1st of October 
of that year, the observations, which up to that period had been taken at every second 
hour of mean solar time, were taken at every hour, and thus in their re-arrangement 
in lunar time, the mean height of the barometer at the different lunar hours became 
better represented than had been the case under the two-hourly system. During the 
first year of the hourly observations, viz. from October 1842 to September 1843 in- 
clusive, the examination of the moon’s influence continued to be carried on at the 
observatory by Captain Smythe in a somewhat modified manner, which is thus de- 
scribed by him: — “The hourly observations for each day, extracted from the day- 
book, were grouped into lunar months, and the monthly mean for each hour found. 
The observation taken each day at the hour nearest the time of the moon’s meridian 
transit was inserted in the centre column for that day, and the other observations dis- 
posed right and left in order. As however the observations in this state are affected 
by the diurnal variation, which at St. Helena is very regular and considerable, and 
by which the moon’s effect would have been overridden, the monthly mean for the 
hour was subtracted from each observation taken at that hour, and the remainder 
regarded as due to the moon’s action. When only twenty-three observations inter- 
vened between two meridian transits of the moon, the middle observation was entered 
in both the —12 and +12 column.” 
