112 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



of cyclonic formations, which can only persist by the aid of such 

 exterior sources as furnish the necessary energy. 



(3) The movement of a disturbance towards the pole increases 

 its vitality, and vice versa. 



(4) As the friction increases, the vitality of a disturbance 

 diminishes. Since friction [internal friction or viscosity] is greater 

 in moist air than in dry air it follows that a disturbance should 

 lose vitality when approaching moist vapors, and vice versa. 



Ordinarily barometric maxima follow this rule quite closely, but 

 the minima seems to behave contrariwise and very persistently 

 so. This fact shows again that the cyclone of the temperate zone 

 is essentially a thermodynamic disturbance while the anticyclone 

 is a mechanical disturbance. Thus we explain the profound dif- 

 ference that exists in all respects between these two kinds of whirl- 

 winds which are so similar in appearance. 



(5) The intensity of any disturbance, or the product v R, cer- 

 tainly increases in proportion to the distance from its center, for 

 the atmospheric currents become more and more nearly horizontal: 

 hence follows the following very interesting theorem: 



The vitality of a cyclone diminishes in passing from its center 

 towards its boundary which causes an excessive sensitiveness at 

 the latter; when the cyclone is extensive with a very deep depression 

 its exterior isobars vary incessantly. On the contrary the anti- 

 cyclone has permanent and firm contours and its center of high 

 pressure moves hither and thither without exerting any influence 

 whatever on the boundaries of the whirl. 



Because of this difference the collision between these two classes 

 of disturbances acts destructively upon only one of the two, that is, 

 the cyclone, which eventually is destroyed or modified. 



From the preceding we see that equation (8) gives us a fairly 

 probable as well as general representation of the characteristics and 

 motions that belong to atmospheric disturbances, excepting only 

 one of the most important of the movements, that is, the progressive 

 motion of the whirlwind itself. The direction and velocity of this 

 movement are determined principally by the diurnal rotation of the 

 earth, which action becomes stronger in proportion as the height 

 of the whirl is greater. Now Ave are not yet able to study this action 

 because the law according to which the friction of the air varies with 

 altitude is at present wholly unknown. However, we hope that the 

 current exploration of the atmosphere with kites and sounding bal- 

 loons will not fail to clear up this question, which is as interesting 

 from a purely scientific point of view as it is important for the 

 practical forecasting of the weather. 



