ON THE ROTATION OK ASCENDiNti UODIES. 



245 



therefore only an exemplification, on a gigantic scale, of what is witnes- 

 sed in the whirlwind, and the flowing of water from a funnel. 



In speculating upon the physical cause of these phenomena I had, 

 as early as 1839, come to the conclusion that they had their origin in 

 the revolution of the earth on its axis, and, in endeavoring to explain Red- 

 field's theory of storms, had recourse to that as the cause of their rotation. 

 Neglecting to communicate these views to the public, until I should be 

 fully satisfied of their truth by further observation and reflection, I had 

 the pleasure of seeing them presented in an interesting paper by Charles 

 Tracy, and published in Silliman's Journal for July, 1843. 



To explain these views concisely, let us suppose two particles of air 

 on the same meridian, one at 28° and the other 

 at 30° north latitude, to start towaids a point be- 

 tween them at 29°, (see Fig. 1.), they could not, 

 in consequence of each having the velocity of ro- 

 tation of the earth due to its latitude, meet at that 

 point. The velocities of rotation at the several 

 latitudes of 28°, 29°, and 30°, are 915.1, 906.6,29° 

 and 897.6 miles per hour. Consequently if an 

 hour were required for these particles to pass 

 from 28°, and 30° to the intermediate parallel 

 of 29°, the southern particle, having 8.5 miles' 

 greater eastward velocity than the point A, would, after the lapse of an 

 hour, be found that distance east of that point, and in like manner the 

 northern particle N would be found, at the same time, 9 miles west of 

 that point, or the two particles N and S would be 17.5 miles apart, each 

 having moved in a curve more and more inclined in its respective direc- 

 tion. The same would happen with all other particles starting from the 

 same or adjacent points. Now as these curves are oblique to each other 

 the moving particles would have a tendency to communicate to the mass 

 of air, through which they must pass, on opposite sides, motion around 

 that point precisely in the direction indicated, viz : from right to left. — 

 (See Fig. 2.) 



But to reduce this from the large scale, on 

 which the extended storms take place, to that which 

 exists in the smaller thunder-cloud, the vorticular 

 motion of a fluid in a funnel, and the smaWpilol bal- 

 7oons,letus suppose that, in latitude 40°, two parti- 

 cles of air, in a circle of three feet in diameter, were 

 to start from opposite points towards the centre, 

 and if it required them one second of time to 



23' 



