THEORY DEDUCED FROM PHYSICAL LAWS. 9 



vanced to E, the wind to observer C will be changed round 

 to north, and to observer D to south, blowing at that time 

 with its greatest violence ; whilst to observer E, it will be 

 calm, without having changed its direction, only having 

 gradually increased in violence, as the borders of the storm 

 approached, and gradually diminished in violence as the 

 centre approached. Moreover, if the storm is very violent 

 and not very wide, the barometer at E will be very low 

 when the centre of the storm is there, and there will at that 

 time be no rain; for the upward motion of the air will 

 carry with it the drops of rain, and throw them off at the 

 sides ; but, in the mean time, it will continue there very dark 

 and cloudy. 



As the storm passes onwards towards B, the wind will 

 suddenly commence blowing from the west at E, increasing 

 in force there for some time after it begins to diminish its 

 violence at C and D, where it is now changing round re- 

 spectively to west of north, and west of south. In like 

 manner it may be shown, if the storm moves in any other 

 direction, that this direction may be ascertained by a single 

 observer, provided the storm is round. 



25. If the velocity with which storms travel along the 

 surface of the earth shall be ascertained, then not only their 

 direction but their distance from a single observer may be 

 known from the angular velocity with which the wind 

 changes. 



26. If it should be found, by further observation, that the 

 uppermost currents of the air give direction to storms, it 

 seems probable that near the equator they will be found to 

 move from east to west. For, on the principle of the con- 

 servation of areas, when the air at the equator rises ten 

 miles from the surface of the earth, it will be ^ F farther 

 from the centre, and of course it will fall back towards the 

 west by more than ^J^ of the equatorial velocity of the 

 earth, eastwardly by its diurnal motion, or about two and a 



2 



