53 8 THE POPULAR SCIENCE MONTHLY. 



sense was brought into play in courtship, and that colors and 



pattern have been gradually modified by the preference of the 



females for the most beautiful males ; he believed that such 



sexual selection accounts for many of the most beautiful features 



possessed by animals, viz., those which are especially displayed 



during courtship. 



♦*♦ 



THUNDER-STORMS. 



By EOBERT H. SCOTT. 



THUNDER-STORMS naturally attract universal attention 

 when they occur, and it may perhaps be of interest to point 

 out some particulars that have been ascertained about them. 



The most obvious facts -are that a heavy cloud passes over the 

 observer, and that from it lightning appears, followed, after a 

 greater or less interval, by thunder ; and that usually heavy rain 

 or hail falls from the cloud. The damage wrought by these oc- 

 currences, whether by lightning-strokes or by the hail, is so seri- 

 ous that, in countries especially liable to such visitations, hail in- 

 surance forms an important item in the farmer's calculations. In 

 many countries such insurance is in the hands of the Government, 

 and accordingly statistics as to the amount of losses are to be ob- 

 tained ; whereas where insurance is in the hands of private com- 

 panies, information as to the expenditure of these companies is 

 naturally not published. 



As regards the liability of certain districts to suffer damage 

 from thunder-storms, it has been maintained by several authorities 

 that these visitations are steadily increasing in frequency. A 

 most elaborate inquiry into the records of such occurrences was 

 printed in the Journal of the Statistical Office of Berlin for 1886. 

 From this it appears that the evidence indicated no general in- 

 crease in the frequency of lightning-strokes, but, on the contrary, 

 rather a decrease. Houses with soft or, in other words, thatched 

 roofs are struck about seven or eight times more frequently than 

 ordinary slated dwelling-houses. Houses in towns are much less 

 frequently affected than those in the country. 



The geological character of the soil has a very great influence 

 on the risk. If this for a limestone soil be taken as one, that for 

 a sandy soil is nine, and for swampy land twenty-two. As regards 

 the different classes of trees, if the risk to a beech be taken as one, 

 that to a conifer (fir or spruce) is fifteen, to an oak fifty-four, and 

 to other deciduous trees forty. Another investigator accounts for 

 the comparative immunity of the beech by the fact that its leaves 

 are edged with short hairs, which allow the electricity collected in 

 the leaves to escape quietly. 



As to the actual origin of atmospheric electricity, authorities 



