352 SCIENTIFIC RECORD FOR 1884. 



(Ira wu into the fire of a burning forest ; at some distance this draft was 

 noticeable by the lowering of the lower portion of the clouds. 



10. Subsidiary whirls formed under favorable circumstances. {Z. 0. 

 G. M., XIX, p. 202.) 



307. William M. Davis, of Cambridge, writing to Dr. Koppen in refer- 

 ence to the simoom [German, Samum], the latter replies by quoting the 

 following as the characteristics. of the simoom as experienced in the 

 Indian deserts by Dr. Henry Cook : 



Its beginning is sudden; occasionally a cold current of air precedes 

 it; it occurs ordinarily in the hot months, June and July ; it occurs in 

 the night as well as by day ; its path is straight and definite ; its pas- 

 sage leaves a narrow trail behind ; it burns and kills the animals and 

 vegetables in its path ; it is accompanied by a very noticeable smell of 

 sulphur; it is described as like the current of air from a furnace, and 

 certainly the temperature of the air within it is very high ; it is not 

 accompanied by either dust or thunder and lightning. 



Koppen shows that, assuming the rise of temperature in the simoom 

 to be 10° C, then, if the air has been thus heated by the compression 

 of a descending current, it must have descended about 4,000 meters; 

 but he thinks it not at all plain why the air should descend to the 

 earth's surlace. There is not a perfect parallelism between the simoom 

 and ordinary Boen, nor an antithesis between Boen and thunder- 

 storms. {D. M. Z., I, p. 245.) 



308. A. Klossowskij hasjliscussed the observations of thunder-storms 

 made in Kussia by the observers of the Geographical Association since 

 1871. This series of reports was inaugurated at the instance of A. 

 Woeikof, who also published the results for the first year (1871). The 

 present volume gives a comi)lete summary of the work since that time. 



309. J. Ludevig presents the results of the observations of thunder- 

 storms made during 1882-'83, at the Government telegraph stations in 

 Germany. The maximum number of storms occurred in May, 1882, but 

 this was api)arently abnormal ; the normal maximum appears in July, 

 1882, and again in July, 1883. The maximum number of days on which 

 thunder-storms occurred was 28 in June, 1882, and 30 in June, 1883, 

 The storms came most frequently from the southwest and next fre 

 quently from the west ; the hours during which most storms occur is 

 from 3 to 4 P. M., and the minimum frequency of storms from 12 to 3 

 A. M. {Z. 0. G. ill., XTX, p. 429.) 



310. Dr. P. Audries, in a memoir on formation of thunder storms and 

 hail, after a review of the older literature on the subject, adopts me- 

 chanical theories ver^^ similar to those of Ferrel in his Meteorological 

 Eesearches, part 2, With regard to the formation of a potential suf- 

 ficient to produce lightning, he adopts the view that this is explained 

 by the combination in one of numerous small diops of water; as to the 

 origin of electricity on these small particles, he attributes that to friction 



