OF THE WIND AND BAROMETRIC PRESSURE AT BOMBAY. 
9 
circle of the globe, would transfer a sensible fraction of the whole atmosphere backwards 
and forwards.” 
Whether such a system of diurnal wind-currents as that which has been supposed, 
having a second complete oscillation during the night, is really a universal phenomenon, 
must be determined by extended observation and investigation in other localities ; and 
whether the currents are originated and propagated in the manner that has been sug- 
gested, or whether they do not rather owe their origination in a more direct manner to 
the diurnal fluctuations of the temperature of the air*, it is perhaps premature to 
speculate ; but in the mean time it appears to be worth while to compare the observa- 
tions that are available, with the conclusions that may be drawn from the hypothesis of 
the existence of such currents, and to mark the relations that will be found to obtain 
between the diurnal variations of the wind and other meteorological phenomena. 
9. If such a system of diurnal wind-currents really exists in nature, we should expect 
to find the ordinates of the two curves representing the meridional diurnal variations of 
the wind for the northern and southern hemispheres exactly reversed in direction, that 
they increase in range with the latitude in both hemispheres, and vanish at the equator. 
We should also expect to find that the range of the curve for each place of observation 
has a yearly variation corresponding to the sun’s change of declination, being smallest 
when the sun’s zenith distance is smallest and increasing as it increases, and vice versa. 
Such a variation in range is clearly shown by the mean monthly curves for Bombay. 
They give the following diurnal ranges, which are the differences of the mean ordinates for 
12| and! 8^ hours in each month, measured in the same manner as those given in Table IV. 
Table V. — Ranges of the Meridional Diurnal Variation of the Wind and the Land- and 
Sea-breeze at Bombay, and the Ratios of the latter to the former. 
Jan. 
Feb. 
Mar. 
April. 
May. 
J line. 
J nly. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
Range of meridional va- 1 
riation J 
Range of land- and sea- 1 
breeze J 
Ratios 
61 
61 
3-6 
3 2 
17 
0-8 
02 
1-6 
23 
4*5 
5-9 
5 2 
14-8 
16 1 
17 5 
16 2 
119 
8-5 
2-8 
4 1 
8-5 
14-3 
16 9 
14-9 
2-3 
2-6 
4-9 
50 
70 
106 
140 
26 
37 
3-2 
21 
2-9 
These ranges furnish another argument in favour of the meridional diurnal variation 
of the wind having an origin independent of that of the land- and sea-breeze ; for if both 
were a consequence of the same local influences, they would most probably vary in such 
* The fact that the curve (fig. 8) attains its maximum south position not long after noon (the time when any 
particular place is receiving heat most rapidly from the sun), and before (not after) the time of maximum tem- 
perature, which occurs about 14)- hours, appears to point to a direct action of the heated air in expanding itself 
outwards as well as upwards ; for if the south current were produced solely in the manner suggested by Sir 
John Herschel, we should expect it to attain its maximum strength after the time of maximum temperature, 
not before it. The same feature which has here been pointed out as appertaining to fig. 8 will hereafter be seen 
to exist in similar curves for other places (see figs. 12, 13, and 14). 
MDCCCLXXIII. 
C 
