METEOROLOGY. 351 



cause that is over forty times larger than the second. {Z. 0. O. M., xix, 

 p. 80.) 



304. M. Moller, in Lis investigation on the temperature and move- 

 ment of the air in a Boen, states that in 1880 he first recorded the sug- 

 gestion that the shadows of the clouds caused strong winds, which, 

 acting like gusts, are called Boen, and which accompany the streaks of 

 rain from cumulus clouds. This explanation, however, seemed unsatis- 

 factory, because such wind-gusts occur also at night time, when, of 

 course, there are no shadows. The true explanation has, ho thinks, 

 been given by Koppen, namely, that the falling rain carries with it air 

 from above, which on reaching the ground spreads out and increases 

 the strength of the prevailing wind. Combining his own and Kcippen'a 

 ideas, he develops carefully the structure and growth of a thunder-storm, 

 and succeeds in explaining very satisfactorily the mode of formation of 

 hail and the low-lying scud in advance of the main cloud, and which 

 the observer generally easily recognizes as rising up to feed the advanc- 

 ing edge of the cloud. (D. 31. Z., i, p. 230.) 



305. [Views similar, and in most respects identical with Koppen's and 

 MoUer's, have during the last twenty years been frequently verbally 

 communicated both by Prof. Joseph Henry and the present writer to 

 fellow-s'tudents of meteorology. They date at least as far back as 1838, 

 when 'Espy was in the full tide of his studies of thunder-storms in 

 Pennsylvania, a region where storms are developed to their fullest extent. 



Our hearty appreciation of the views of Koppen and Moller is en- 

 hanced by their own kindly mention of that most genial Of American 

 enthusiasts.] 



306. C. G. Finemann, of Upsala, in a study upon the " trombe," or tor- 

 nado, of June 7, 1882, draws the following conclusions : 



1. The formation of a tornado is characterized by the simultaneous 

 occurrence of great relative and absolute moisture, high temperature, 

 almost perfect calm. 



2. Tornadoes and thunder-storms originate under almost identical 

 atmospheric conditions. 



3. The two i)hcnomena can occur together or separately. 



4. Finley's work seems to suggest that either phenomenon may de- 

 velop from the other. 



5. The tornado here studied certainly consisted in a strong ascend 

 ing current of air, revolving also in a direction opposed to that of the 

 hands of a watch lying face upwards on the ground. 



6. The ascending current formed an inverted cone out of the mate- 

 rial carried up with it, which moved forwards towards the northeast. 



7. The tornado was fed by moist air, which flowed over the earth's 

 surface with increasing velocity. 



8. The moister the air by so much more did the interior velocity of 

 the tornado increase. 



9. The air was precipitated into th© tornado from below, like cold air 



