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Proceedings of the Royal Society 
that in which in the segment A B the N.E. wind blows. Clouds 
apparently moving from the S.W. are often observed in this part 
of the storm, where N.E. wind first begins to exhibit itself. No 
general movement of the air, however, takes place, because it is 
here that it first commences and continues to be generated from the 
still atmosphere ahead, where the curve of outward propagation 
advances upon it. This continued generation also represents what 
takes place in the clouds. Their apparent movement, which is due 
solely to their additional formation, is the result of atmospheric 
changes which must here take place. Hence occasionally they do 
not represent the force and direction of the wind. Similarly sea- 
men often observe a gale approaching from some point to leeward. 
It has been supposed by some writers that the progress of storms 
is due to the area of low pressure being impelled forward by the 
high pressure usually found near their rear, aided by the diminished 
pressure in front, which is due to heat and vapour. If this were 
the case, it is evident that a derangement would take place as 
regards the circular symmetry of the storm and the direction of the 
spirally inblowing winds, owing to the enormous friction which 
these widespread storms would encounter in being pushed forward 
over the earth’s surface. The more evident of these derangements 
would be the steepening of the barometic gradients in front of the 
storm, a result the reverse of what observation shows to take place. 
The Rev. Clement Ley has shown that the isobars are widest, and 
gradient consequently lowest in the front of the storm.* Further, 
if this were the cause of the progress of storms, areas of depression 
would move more rapidly over the ocean than over the land. Pro- 
fessor Loomis has shown, however, that while the average rate of 
* See “ Journal of Scottish Meteorological Society,” vol. iv. p. 149. 
