^>v . \.v\s OF rnr 



we iway judge appiHxrinut el\ N\ hat relation the tidal 

 forces at present under consideration hear to those 

 proceeding from the snn and moon. Aiul also the 

 *?erage ditierenee in height at sunrise and sunset. 

 compare*! with the average dittorenee in height in the 

 northern and southern hemispheres, should appivxi- 

 BMttely show the relation >vhieh the Nvloeiiy of the 

 earth's motion in its orbit bears to the \vKvitv of ihr 

 motion of the solar system through space. For this 

 purpose we should, however, require a moiv extended 

 and more detailed series of observations than wo at. 

 present possess: and we will therefore simply eon- 

 sider to what extent the elearly ascertained diurnal 

 oscillations of the barometer corroborate the theory 

 at present under consideration. 



186. The diurnal oscillations of the barometer form 

 one of its most marked phenomena. From Sir 

 John Herschel's article on Meteorology in the Ency- 

 clopaedia Britannica, we extract the following table 

 which 4 exhibits the amount of its daily fluctuations 

 above and below the mean value, as deduced from the 

 calculations of Kamtz.* The epochs of greatest pres- 

 sure shown on the table are, according to the same 

 authority, generally speaking, about 9 h. or 9J h. A.M. 

 and 10^ h. or lOf h. P.M. ; and the epochs of least pres- 

 sure at 4 h. or 4^ h. P.M. and 4 h. A.M. And there- 

 fore this table does not show the relative amounts of 

 pressure at the hours of sunrise, sunset, mid-day 

 and midnight; but at epochs intermediate bet\\ n 

 those epochs. 



