OF THE WENT) AND BAEOMETEIC PEESSTJEE AT BOMBAY. 
7 
diurnal variation of the wind ; and the same feature has been shown to be present in 
the longitudinal variation also ; hence we naturally infer that the phenomena may be in 
some way interdependent, and are led to inquire after the nature of their relationship. 
Confining our attention for the present to the meridional variation, it is difficult to 
conceive how any local peculiarity of geographical position could so modify the land- 
and sea-breeze (which we have seen follows chiefly, in its principal direction, the same 
law of progression as the temperature of the air) as to cause its law of progression in a 
north and south direction to be so widely different in character from that in the east and 
west direction as the variations in Table I. show it to be ; and much more difficult to 
conceive how that modification (if it may be regarded as such) of the strictly local phe- 
nomenon which we know the land- and sea-breeze to be, should follow a law of progres- 
sion similar to that of the diurnal variation of the barometer, which is perhaps the most 
universal and regular of all meteorological phenomena. It seems far more probable 
that the variation represented by fig. 8 is not a simple modification of the land- and 
sea-breeze by local peculiarities, but an indication of the existence of a double diurnal 
variation in the general movements of the atmosphere, as universal as, and moving syn- 
chronously with, the double diurnal variation of the barometer, but which has never 
before been noticed because of the unsuitable nature of all wind observations made 
before the invention of Bobinson’s anemograph for exhibiting a variation of this kind ; 
and it is not unreasonable to expect that similar variations will be found at other tro- 
pical stations by similarly reducing a sufficiently long series of suitable wind observations*. 
Now regarding that part of the diurnal variation of the wind at Bombay which is not 
directly attributable to the land- and sea-breeze as a universal phenomenon, perhaps 
its most surprising feature is that the hours about noon should occupy a position 
furthest removed to the southward of the mean direction-line A B, a feature which 
appears to be in direct opposition to the principles of Hadley’s theory of the trade- 
winds, which is the theory that explains satisfactorily the land- and sea-breeze, and in 
which the wind is always supposed to blow towards the heated region, not away from 
it as shown by that feature of the variation ; for, according to that theory, we should 
expect to find a decided tendency of the wind to blow from the north at that time in 
the northern hemisphere. And this feature is the more surprising when viewed side 
by side with the more extensive east and west movement, which is in perfect accordance 
with the theory. 
Speaking about the sun’s heating action on the atmosphere, and the effects resulting 
therefrom, Sir J. Herschel has remarked, in his ‘Meteorology,’ art. 172: — “When 
anemometry is further perfected we may expect to trace the influence of this chain of 
causation into a morning and evening tendency of the wind (on a long average of obser- 
vations) to draw towards the points of sunrise and sunset, to compensate the overflow 
from off the heated hemisphere which takes place aloft in a contrary direction.” 
* Observations of the direction of the wind are of no value for this purpose, unless combined with their 
corresponding observations of the velocity (not pressure) of the wind. 
