82 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



excess, which is due to one section of the population (name- 

 ly, infants) and to one class of diseases (namely, bowel com- 

 plaints), there remains an excess in the cold and a deficiency 

 in the warm months, which is due to the diseases of the or- 

 gans of respiration. 12 A, X., 210. 



THE DISTRIBUTION OF THUNDER-STORMS. 



Hildebrand has investigated the distribution of thunder- 

 storms in Sweden for the year 1871, basing his study upon 

 the observations of about two hundred and fifty stations. 

 The number of days on which thunder was observed varied 

 between one, two, and three in March, April, October, and 

 November, to twenty-seven in July. Thunder-storms are 

 found to be less frequent, not only in the cold months, but 

 also as we proceed northwest. With regard to the daily 

 distribution of these storms, he shows that the greatest num- 

 ber have occurred between 4 and 6 P.M. ; the least have oc- 

 curred between 10 P.M. and 6 A.M. The greater number of 

 thunder-storms come from the northwest; whence also come 

 the clouds and wind. Le Verrier has long since shown that 

 in France the thunder-storms occur on the advancing side of 

 the general atmospheric disturbances, and that they follow 

 the movements of the cyclones; but that, on the other hand, 

 many thunder-storms are purely local. Mohn has likewise 

 studied the subject in Norway, and comes to conclusions 

 quite similar to those of Le Verrier. Mohn has furthermore 

 shown that the origin of the thunder-storm is to be found in 

 the ascent of warm, moist currents of air. These latter, how- 

 ever, also develop in connection with volcanic eruptions ac- 

 companied by whirlwinds, and also when the lowest strata 

 of air are overheated in the hottest hours of the day. He 

 therefore classifies the thunder-storms as whirlwind thunder- 

 storms and heat thunder-storms. The former originate on 

 the advancing side of cyclonic storms, and follow their move- 

 ments over entire countries. The latter class originate on 

 the hot summer afternoons, and are to be considered as pure- 

 ly local phenomena. If, however, we combine the observa- 

 tions of Mchn and Le Verrier with those of Breitenlohner, it 

 will appear difficult to make so sharp a distinction as Mohn 

 has attempted, since both causes are acting at the same 

 time; so that extended and regularly advancing thunder- 



