12 
ME. F. CHAMBEES OX THE DIUENAL YAEIATIOXS 
Or we may suppose the figure to represent the winds of a system which revolves 
about the earth with the sun from east to west, and hence each place of observation 
between the two parallels of latitude will successively pass from west to east through 
the various conditions of the several areas. Take, for example, a station situated on the 
equator at the time 6 hours ; air is then flowing towards it from all directions, and con- 
sequently at that time the barometer is rapidly rising ; when the place has advanced to, 
say, 8 hours, air is still flowing towards it from the north and south, but with a less 
velocity than when it was at 6 hours ; air is also flowing towards it from the east but 
leaving it on the west, though less rapidly, and the barometer is still rising, but less 
rapidly than at 6 hours ; when the station has advanced to 9-J hours air has ceased to 
blow towards it from the north and south, and it is importing just as much air from the 
east as it is exporting on the west; the barometer is now stationary and has reached a 
maximum. When the place arrives at 11 hours, the air has begun to flow outwards 
towards the north and south, and more air is leaving it on the west than is blowing 
towards it from the east, and in consequence the barometer has begun to fall. At about 
13 hours air is leaving the place in all directions and the barometer is falling rapidly, 
and continues to fall until the station reaches 16 hours, when air has ceased to flow 
from it towards the north and south, and is leaving it on the east at the same rate at 
which air is being received from the west ; the barometer has now reached its minimum 
position and is again stationary. As the station advances still further, air begins to 
blow towards it from the north and south, and to leave it less rapidly on the east than 
it receives air from the west, and the barometer begins to rise; about 19 hours, air is 
flowing towards the station from all directions and the barometer is rising rapidly, and 
it reaches a second maximum at about 22 hours, when the air has ceased to flow towards 
the station from the north and south and is blowing inwards on the east at the same 
rate at which it is blowing outwards on the west. From 22 hours to 9^ hours the same 
cycle of changes as that which occurs from 9^ hours to 22 hours is repeated, but on a 
less extensive scale. The same results will follow for a station situated north or south 
of the equator, if it be borne in mind that the north and south winds increase in strength 
with the distance of the place from the equator. 
It will be observed that the movements of the barometer deduced from the figure 
are all in accordance with observation. 
14. The curves fig. 9 and fig. 10 are also of some importance, as will presently 
appear, when viewed in connexion with the “ law of gyration ” propounded by Pro- 
fessor Dove ; for they will be seen to accord with some of the results of his investigations, 
viz. the marked tendency of the wind to rotate in a right-handed direction in the 
northern hemisphere, and in the opposite direction in the southern hemisphere. 
15. The whole of the wind which blows at Bombay on any particular day may be 
regarded as made up of three distinct parts : — 1st, that due to the double diurnal varia- 
tion of the wind, and which is most persistent in its character ; 2nd, the land- and sea- 
breeze, which is also very persistent in all except the monsoon months, June, July, 
August, and September ; and 3rd, that wind which remains after the elimination of the 
