386 Second Report of the Meteorological Committee 



divided, not as usual into lunations from full to full or from new 

 to new Moon, but into periods marked by the Moon's passing 

 from south to nortli of the equinoctial. J8y this division the 

 effect (if any) of the ^loon's change of declination comjiensatcs 

 itself, and leaves the solar efifect in evidence. The cause of the 

 prominence thus given to this part of the Sun's agency, appears 

 to lie in the length of its period compared with the ^Ioon's, 

 which gives time for the waters of the whole ocean to ac- 

 commodate their general level to the actual force, by 

 bodily transfer from one part of the globe to another, and by 

 assuming, at each instant, (what the Tides of short period have 

 never time to do,) very nearly tlic figure of equilibrium due to 

 this particular modification of the disturbing forces. 



Observed mean positions of the mid-water mark on the float of the 

 Tide-gage at Simon's ^ay, during successive intervals of the Moon's 

 Transit from North to South of the Equinoctial. 



Limit! of intervals. 



JVo. of 



Tidvs 



ohserved 



Heights of 



mid-mater on the 



Gage. 



Remarks. 



At the Meetings of the Institution of Wednesday, Septem- 

 ber 3, and October 1, Sir J. Herschbl stated that he had ex- 

 amined the Meteorological Journal kept at the Port Office by 

 Sfr. M'Cleod, under the direction and supcrintendance of 

 Capt. Bance, during 58 months, commencing with October 15, 

 1828, in which are registered the heights of the Barometer 

 with the temperature of the instrument, for the hour of 9 a.m., 

 noon, and 3 p.m., with the usual notices of wind and weather, 

 and that having reduced and interpolated them by graphical 

 projection, ho had been led to the following conclusions : — 



1st. That the atmospheric pressure at Cape Town is subject 

 to a considerable and very regular annual fluctuation amount- 

 ing (when reduced to a temperature of 32' Fahr.) to . 287 i". 

 — the highest level being attained about the 16th of July, and 

 Ihe lowest about the 16th of January, on an average of 5 years. 



2d. That the Barometric pressure is also subject to a re- 

 gular diurnal fluctuation, whose average amount on a mean of 

 the whole year may be stated at . 027 in.; the highest pressure 

 taking place at or about 9 a.m., and the lowest (so fur as can 

 be gathered from observations made only at the hours abovc- 

 jiamed) at 3 p.m. 



