398 
The following are the extreme variations from the daily mean pressure for 
ALEXANDER BUCHAN ON THE 
January, April, July, and October, at Bombay for six years :— 















A.M. P.M. 
Inch, | Hour || ncn, | Hour. | tach, | Hou | ghey. | Hour 
January, . : —'028 | 3-4 +7068 | 9-10) —‘O051 | 4 — 022 10 
April, . : : —'028 | 3 +063 | 9 —'055 | 4 —'019 |} 10 
July, . 2 : —'031 | 3-4 +°037 | 10 —'030 | 4- — 024} 10 
October, ; 3 — 029 | 3 +°063 | 9 — 031 - — 022), 9 


Similarly, the maxima and minima at Vienna for ten years, with the hours 
of their occurrence, are as follows :— 



















A.M. P.M. 
ae Hour. cae Hour. oo Hour. _—_ Hour 
January, — 008 6 +°018 | 10 — “020 3 +012 | 10 
April, . — 0038 5 +021 10 — ‘027 5 +°014 11 
July, . + 003 3 + °022 9 — ‘028 5 +009 11 
October, —= O10 10 6 2020) JO —015-| .4~. | +0084 16 




These illustrations may be regarded as typical, to a large extent, of the 
diurnal barometric fluctuations in tropical and temperate regions. At Bombay 
the amounts are large, and the times of occurrence of the maxima and minima 
pretty regular from 3 to 4and 9 to 10 A.M. and p.m. On the other hand, the 
oscillations at Vienna are much smaller in amplitude, and the times of occur- 
rence of the critical phases take place through wider intervals, being from 3 to 6 
and 9 to 11 A.M. and P.M. 
If only the amount of the whole of these diurnal oscillations be taken into 
consideration, which at Bombay average 0-155 inch, they might well be classed 
among the most remarkable of atmospherical phenomena, but when the regu- 
larity of their occurrence from day to day, and their quasz tidal circuit round 
the globe are considered, they will be at once recognised as the most important 
of all atmospheric fluctuations. It is remarkable that, though they are among 
the best marked of meteorological phenomena over at least two-thirds of the 
globe, yet none of these phenomena, with the exception perhaps of electrical 
phenomena, could be named respecting whose geographical distribution so little is 
known, whether regard be paid to their amounts, the times of occurrence of the 
critical phases, or the physical causes on which the differences depend. What, 
therefore, is required, in the first place, is a sufficient number of facts to show 
