344 SCIENTIFIC RECORD FOR 1884. 



has a relative number 40, while from 6 p. m. to midnight the number is 

 32. More than two-thirds of the thunder-storms come from the west 

 and depart toward the east. The wind prevailing during the storm is 

 most frequently" from between west and north. In general rain accom- 

 panies thunder-storms, and this is more intense in the hilly regions than 

 in the plains. The monthly frequency of hail is nearly the same as the 

 annual frequency of thunder-storms. The second portion of Ferrari's 

 work, or the study of the mechanism of a thunder-storm, is the larger 

 and more important. He gives here detailed studies of those storms 

 that occurred between April 30 and Sej)tember 17, and for each of 

 which he has at least a hundred observations ; charts are published in 

 full of ninety-five storms occurring on twenty-eight days. The charts 

 show the hourly isochromes for the beginning and end of each storm. 

 Ferrari has drawn these lines after smoothing away individual differ- 

 ences; a process that may, however, hide from notice some important 

 phenomena. The cold air that accompanies or immediately succeeds a 

 thunder-storm is by Ferrari exj)lained as due to a ra^jid descent of the 

 air from the higher regions, but this is opposed by Dr. Lang, who 

 thinks it is rather due to the cooling of the air by precipitation, espe- 

 cially hail. The intensity of the thunder and lightning is, after allow- 

 ing for local influences, more considerable in extended typical thunder- 

 storms than in those of small dimensions, and increases as the annual 

 curve of temperature rises. Ferrari finds that distant heat lightning 

 does not exist except in connection with thunder-storms there present. 



292. [It was Professor Henry who first showed that in such cases the 

 thunder from distant storms might in its progress downwards towards 

 the observer suffer total reflection, and thus be carried over him above 

 his head.] The shapes of the thunder-storms are generally long bands. 

 In general Ferrari's conclusions are in agreement with those quite in- 

 dependently evolved a little later by von Bezold from his studies in 

 Bavaria. {Z. 0. G. M., xix, p. 353.) 



293. Prof E. Landolt, from an elaborate study of the severe hail and 

 thunder storms of the 21st of July, 1881, arrives at the following con- 

 clusions : (1) In very heavy thunder-storms the clouds are only a hun- 

 dred meters above the earth, and the hail-stones form in the lowest strata 

 of air; (2), the topography of the earth has a great influence upon the 

 distribution of the storms ; (3), the directions of the strongest currents 

 of air dependent upon the thunder-storm follow the axis of the storm, 

 and sometimes precede it, and the air flows from both sides toward the 

 storm-center; (4), forests, especially when they crown the hilltops, mod- 

 erate the extent and severity of the hail ; (5), the hailfall can be very 

 severe even on high regions that extend near to the thundercloud. 

 {Z. O. Q. M., XVII, p. 254.) 



294. Prof. W. von Bezold, of Munich, gives an account of the methods 

 pursued by him for investigating thunder-storms in Bavaria and Wur- 

 temburg. The ordinary postal card is converted into a form for the 



