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also exhibited brass plates designed by Mr. D’Alquen, and having 
central black spots of different sizes, to be used with transparent 
objects, when it was wished to see them as opaque objects with the 
Leiberkuhn. 
APRIL 9TH. 
ORDINARY MEETING.— MR. F. E. SAWYER ON 
“WINDS,” - WITH | -REFERENCE TO --THOSE 
PREVALENT IN SUSSEX. 
Solar heat was the chief cause of the winds. The principal winds 
were formed near the equator. The air in the tropics became heated 
and expanded, and thus being lightened, ascended ; cold air from the 
poles rushed in to supply its place, and so two currents of wind were 
formed, the upper current of warm air flowing from the equator to the 
poles, the lower one of cold air from the poles to the equator. The 
revolution of the earth caused these currents to diverge, and in the 
northern -hemisphere turned the warm upper current into the south- 
west wind, and the cold lower current into the north-east wind; and 
in the southern hemisphere the upper current into the north-west wind 
and the lower into the south-east. The upper currents did not descend 
* to the surface for some time after leaving the equator, and consequently 
in the northern tropical belt the north-east wind prevailed, and in the 
southern tropical belt the south-east wind, and these winds are known 
as the “Trades.” Ata distance of about 30 degrees from the equator 
the equatorial currents descended to the earth, and came into collision 
with the polar currents, causing violent storms in these regions. 
If all parts of the earth maintained throughout the year the same 
relative position with regard to the sun, the four winds described would 
blow without intermission, but in the summer the northern hemisphere 
was inclined 23$ degrees towards the sun, and in the winter the same 
distance away from it. The earth’s axis was only vertical on March 
21st and September 21st in each year. This difference in position 
disturbed the four principal wind currents, and made them more 
variable, and probably was the cause of the “monsoons” which blow in 
the Indian Ocean. The north-east monsoon blew from November to 
March, and the south-west monsoon from the end of April to the middle 
of October. These periods coincided almost entirely with the periods 
during which the northern hemisphere was inclined to and from the sun. 
