260 ANNUAL OF SCIENTIFIC DISCOVERY. 



explosions must follow, in the same way as the Leyden jar explodes spon- 

 taneously when surcharged to overflowing. Were it not for the lower cloud 

 and its negative condition, the surcharged drops of rain would scintillate 

 their electrical fire as they touched the earth. 



Thunder-storms rage more violently as they pass over forests and moist 

 places, and were it not for the deposition of rain as they pass along their 

 track, would exhibit a parched trail. A long drought is adverse to the gen- 

 eration of a thunder-storm, and on the other hand a moist earth is promotive 

 of one. 



Thunder-storms are deflected from their courses, as well as retarded in 

 their movement, by friction on the earth. Ascending from the earth with a 

 balloon in the rear of a storm, and mounting up a thousand feet above it, 

 the balloon will soon override the storm, and may descend in advance of it. 

 I have experienced this several times. 



ON THE DIRECTION OF THE WIND. 



Professor Hennessy, at the last meeting of the Britith Association, stated, 

 as the result of his observations with an improved annemometer, that the 

 wind rarely blows in a perfectly horizontal direction. The deviations from 

 that direction, although usually very small, are sometimes very remarkable, 

 and follow each other in such a way, especially during strong breezes, as to 

 indicate a species of undulatory motion in the wind. 



ON THE SPIRALITY OF MOTION IN WHIRLWINDS AND TORNADOES. 



The following important paper was read before the American Association 

 for 1856, by the late W. C. Redfield, and subsequently published in Silli- 

 man's journal. 



1 . An aggregated spiral movement around a smaller axial space, consti- 

 tutes the essential portion of whirlwinds and tornadoes. 



2. The course of the spiral rotation, whether to the right or left, is, one 

 and the same in this respect throughout the entire whirling body, so long as 

 its entegrity is preserved. But the oblique inclination which the spiral 

 movement also has to the plane of the horizon, is in opposite directions as 

 regards the interior and exterior portions of the revolving mass. Thus, in 

 the outwi-rd portion of the whirlwind the tendency of this movement is ob- 

 liquely downward, where the axis is vertical ; but in the interior portion, 

 the inclination or tendency of the spiral movement is upward. This fact 

 explains the ascensive effects which are observed in tornadoes and in more 

 diminutive whirlwinds. 



3. Owing to the increased pressure of the circumjacent air in approaching 

 the earth's surface, the normal course of the gradually descending move- 

 ment, in a symmetric whirlwind, is that of an involuted or closing spiral; 

 while the course of the interior ascending movement of rotation, is that of 

 an evolved or opening spiral. Hence, the horizontal areas of the higher por- 

 tions of the whirl exceed greatly those of its lower portions. 



