142 On Dust Whirlwinds and Cyclones. [No. 2. 



of the equator, rotate from right to left Q) and those to the South 

 of the equator from left to right \j. 



Having therefore determined the probable track of a rotatory storm 

 - — face the point to which the storm is supposed to be travelling — the 

 stronger centripetal winds will then be found blowing on the right 

 hand in the Northern Hemisphere — and on the left hand in the 

 Southern. 



The stronger centripetal winds on the side of progression, must for 

 the reason above-stated, blow more or less in the direction of the 

 storm's track ; while those on the opposite side of the whirling ellipse, 

 will be opposite to it, and much more limited in extent. 



The Diagram of PI. 3 indicates more plainly what I have attempted 

 to explain. 



I have there described the winds surrounding the electrical zone as 

 strait-lined winds, blowing from a circumference to a centre, as centri- 

 petal tangents ; which centre is the revolving ellipse or zone, forming 

 the body of the Cyclone. 



The mass of electrical matter of which the body of the Cyclone is 

 composed, descends I presume, as in the case of the small whirlwinds 

 from the sky to the earth, in the form of a spiral, working downwards ; 

 and its subsequent movements and the track, may depend in a great 

 measure on causes connected with the earth's rotation, and upon the 

 prevailing surface winds. 



To illustrate this idea of the progression and rotation of a Cyclone 

 in a definite course, spin a tee-totum provided with a glass tube drawn 

 out to a fine point, containing ink, on paper laid perfectly flat. 



"When the tee-totum is what boys call asleep, give it a slight puff 

 with the breath, horizontally ; this will cause an obliquity of the axis 

 of rotation, and at once induce a revolving motion, and also a progres- 

 sive one in some particular direction ; and the toy will be found to 

 describe exactly the peculiar motions of the Cyclone, both rotatory 

 and progressive, and by spinning it one way or the other, familiar 

 illustrations may be afforded of the manner in which a Rotatory storm 

 works in the Northern and Southern Hemispheres. 



An explanation of the law of the rotations may be attempted 

 thus. — 



The rapidity of the earth's diurnal rotation from west to east, 



