368 



H. W. Dove on the Law of Storms. 



fruitful principle I am now prepared to explain theoretically 

 the phenomena of storms. 



Let a b be a series of material points parallel to the equator, 

 which are set in motion by a certain impulse in the direction 

 a t from south to north. The rotation of the earth combined 

 with this impulse will produce a motion of a b towards g h, if 

 the space d b h is void of matter. But if this space is filled by 

 quiescent matter, the particles at b will, as they move, come 

 into contact with particles in the space dbh, which rotate with 

 less velocity; their motion in the direction of east will there- 

 fore be retarded, and the point b will move not towards h but 

 towards^ The particles at a are, on the contrary, in juxta- 

 c d e f g h 



position with particles, which at first have an equal velocity 

 of rotation, and consequently move as they would in a vacuum, 

 that is, towards g. If, then, a b represent a mass of air im- 

 pelled from south to north, the storm will have a more 

 southerly direction at the east side, a more westerly one on 

 the west side, and will thus acquire a tendency to whirl in 

 the direction S.E. N.W. This tendency to whirl would 

 not take place, were there no resisting matter in the space 

 d b h, and will therefore increase in proportion as this resist- 

 ance prevents the course of the storm from deviating towards 

 the west. Now within the north tropical regions the space 

 dbh is filled with air, which flows from N.E. to S. W. Here, 

 therefore, the resistance is at a maximum, and the air at b 

 has its westerly tendency so far checked, that it retains its 

 original direction towards d almost unaltered, whilst, on the 

 other hand, the air at a has acquired a tendency to move to- 

 wards d. The storm accordingly will whirl with the greatest 

 intensity, but retains its initial direction and lateral magnitude. 

 So soon, however, as it reaches the temperate zone, it finds itself 

 in contact with air at dbh, which is in motion from S.W. to 

 N.E. The resistance, which the particles at b experience, 

 will therefore be considerably diminished, or even almost 

 vanish, that is to say, the direction b d is transformed into the 

 direction b h, and the storm bends round almost at a right 



