420 



RECORD OF SCIENCE FOR 1887 AND 1888. 



times seeu liigli up at Ihe base of ibe tbuiider storm uow reaches down 

 to the earth, and the violent winds due to its up-draft cause great de- 

 struction. These storms occur usually in the broad currents of warm, 

 moist southerly winds that prevail on the south and east sides of an area 

 of low pressure or general storm center ; they are in fact whirls within 

 whirls, and may be expected as likely to occur when on the morning 

 weather map the depression of the dew-point is reported as only a few 

 degrees, and southerly winds cover the country, blowing toward a storm 

 center in the northwest, or lake region. 



(Tile preceding paragraph as written in 1883 expresses a generaliza- 

 tion familiar to me since boyhood and in agreement with views of Espy 

 and many writers; the conviction of its general truth had led me in 

 1871 {ind 1872 to frequently publish in the official daily weather predic- 

 tions the paragraph, " Conditions are favorable for severe local storms." 

 Any discussion as to the original author of this generalization would 

 carry us back to the first weather charts of Leverrier 1858, Henry 1850, 

 Espy 1838, Loomis 1838, and Kaemtz 1835, and Brandes 1828.) 



The number of tornadoes likely to occur in any State in any one year 

 is shown approximately by the figures in the sixth column of the fol- 

 lowing table, as copied from Finley's " Character of Six Hundred Torna- 

 does," first edition, 1882 (the second edition April 1884, would not ma- 

 terially change these figures); but the relative geographical distribu- 

 tion is only fairly shown by adopting some such unit of area as 100 miles 

 square or 10,000 square miles, for which unit we find the annual average 

 frequency given in the seventh column. The last column of this table 

 should replace the misleading statement of the number of tornadoes on 

 record in any State, without considering the area of the State or the 

 number of years and observers involved in getting together the lists. 



Table of frequency of tornadoes in each State. 



State or Territory. 



Alabama 



Alaska 



Arizona 



Arkansas 



California 



Colorado 



Counoctifut 



Dakota 



Delaware 



District oC ('uliiniliia 



Florida 



Georgia 



Area in 



units of 



10,000 



square 



miles. 



5.1 



51.7 



11.4 



5.2 



15.8 



10.4 



0.5 



15.1 



0.2 



0.0 



,5.9 



5.8 



Finley's record. 



Total 

 number 



Lengtb 

 of record 



42 



Tornadoes from 1874 to 1881, 

 inclusive (eight years 

 complete). 



Finley's 

 numbers. 



Annual 

 Annual ' average 

 average iper 10,000 

 per state, square 

 miles. 



12 



0. •-' 

 1.0 



(1.1 



0. 1 

 0.2 



1.1 



(I. di' 

 (». I!» 

 0.01 

 0. 01 

 40 

 0.07 



0.6 

 3.0 



0. 10 

 0.G2 



