July i8, 1918] 



^NATURE 



397 



barnyard poultry; doors and windows blown out; soot 

 rises from chimneys; mud penetrates clothing. 



Property damage in the United States due to tor- 

 nadoes varies greatly from year to year, depending, 

 as it does, upon the •accidental" passage of tornadoes 

 through well-populated or through sparsely settled 

 districts. In half an hour the St. Louis' tornado 

 (May 27, 1896) destroyed property to the amount of 

 10,000,000 dollars in St. Louis alone. In some vears 

 the damage for the whole United States falls to but a 

 few hundred thousand dollars. 



Fig. 2 illustrates the tragic fate of one familv in a 

 tornado (May 30, 1879).- A house was moved entirely 

 from its foundation to the south-east, then broken to 

 pieces and scattered along the tornado track to the 

 north-east for more than a mile. The members of the 

 household, consisting of father, mother, and four 

 children, ran outdoors as the storm came. They first 

 turned north-west, but, thinking that the tornado was 

 coming towards them, they turned towards the east. 

 One by one they were caught up and carried by 

 the wind. The father and baby were carried 150 yards 

 into a field to the north-east, and found in the agonies 

 of death. The mother was carried eastward seventy- 

 five yards, and dashed against a tree, around which she 



W'J >i.e N3>ivr^ 



1- IG. 2.— lornado. May 30 1879. From the Quarterly Journal of 

 the RoyaP Meteorological Societj-. 



was partially twisted ; her skull was crushed, and her 

 clothing was stripped from her body. A girl was 

 found dead, fifty yards north-east of the house, in the 

 direct path of the storm. A boy was blown" into a 

 haystack forty-five yards to the north-east, and a girl 

 was found eighty vards to the north-east lying in the 

 tornado track. Neither of these two children was 

 seriously injured. Disasters similar to this one come 

 all too frequently in the American tornado belt. 



Finley listed some 600 tornadoes, of which forty 

 were fatal to human life, causing a loss of 466 lives 

 and injuring 687 persons.' In the case of the St. 

 Louis tornado (May 27, 1896) the loss of life was 306. 

 In fact, in this one storm the fatalities and the 

 damage to property were greater than in anv other 

 single tornado on record. Prof. Mark W. Harrington, 

 formerly Chief of the U.S. Weather Bureau, estimated 

 that the chance that a tornado may, in anv vear, 

 cross the particular locality where any individual may 

 ha{>pen to be is i in 625,000, and " not worth worry- 



- J. P. Finley, " Report of the Tornadoes of May 29 and yi in the States 

 Xansas. Missouri. Nebraska, and Iowa," Professional Papers, U.S. Signal 

 ce. No. iv. (Wa'^hingion, n.C, i88i.) 



i. P. Finley. "Report on the Character of Six Hundred Tornadoes." 

 ■•'ssional Papers, U.S. Signal Service, No. viii (Washington, D.C., 



NO. 2542, VOL. lOl] 



ing about."* The late Prof. Cleveland Abbe concluded 

 that even in the so-called " tornado States " the prob- 

 ability of tornado destruction is less than that of 

 lightning or fire.* 



Distribution of Tornadoes in Place and Time. — The 

 real home of the tornado is over the great lowlands 

 east and west of the Central and Upper Mississippi and 

 of the Lower Missouri valleys, and, to a less marked 

 degree, over some of the southern States. Tornadoes 

 are rare west of the looth meridian, and very rare 

 or unknown in the mountain areas. They have been 

 reported from all States east of the plains, but de- 

 crease markedly in frequency towards the north. They 

 are rare in the Appalachian Mountains, and also in- 

 frequent along the Atlantic and Gulf coasts. The 

 widespread impression that tornadoes are increasing 

 in number in the United States is without foundation 

 of fact. Tornadoes are reported with greater accuracy 

 than formerly, and they are likely to do more damage 

 than they used to do because the country is more 

 densely populated. 



Tornadoes may appear in any month, and at almost 

 any hour of the day or night. Like thunderstorms, 

 however, they distinctly prefer the warmer months, 

 and the hours closely following the warmest part of 

 the day. Thus spring and early summer (April-July) 

 and 3-5 p.m. are their favourite times. 



Tornado Weather Types. — Tornadoes have much 

 in common with thunderstorms. In fact, they are, in 

 reality, special local developments, of greater violence, 

 in connection with severe thunderstorms. The general 

 conditions which produce these two phenomena are, 

 to a large extent, identical. The essential difference 

 comes in the formation of the vorticular whirl in the 

 tornado. Thus, like the largest and most severe 

 American thunderstorms, tornadoes occur as attendants 

 of the parent cyclones of which they are the offspring. 

 They are born, in the large majority of cases, in the 

 area of warm, damp southerly winds flowing north- 

 ward from the Gulf of Mexico in front of a general 

 cyclonic storm. This storm is usually more or less 

 elliptical or V-shaped, its major axis extending north 

 to south or north-east to south-west from the Great 

 Lakes, across the central lowlands well into the 

 southern States. The "wind-shift line" or "critical 

 axis" is usually well marked. North and west of the 

 wind-shift line northerly to westerly winds are blow- 

 ing, with relatively low temperatures, and not infre- 

 quentlv with rain or snow. South and east of the 

 critical axis there is a great flow of southerly or south- 

 westerly winds with higher temperatures, usually 

 sultrv and oppressive weather, and often with rain 

 squalls. When conditions are favourable, tornadoes 

 are likelv to occur in a district some 300, 400, 500, or 

 more miles to the south-east, south, or south-west of 

 the cvclonic centre, near, but usually to the east of, 

 the wind-shift line. Here the contrast between the 

 warm, damp southerly and the cool, dry northerly and 

 westerly winds is sharp. Here is inevitably a zone 

 of great disturbance ; of over-running, under-running, 

 and mixing; of turbulence.; of instability; of local 

 whirls. Here, aided by the local warming due to sun- 

 shine, are favourable conditions for breeding thunder- 

 storms and, fortunately much less often, for develop- 

 ing tornadoes. The parent cyclone may travel many 

 fhousands of miles, a good part of the way round 

 the world, vet in only one portion of its long course, in 

 the Mississippi valley region of the United States, and 

 usually only at one time of the year, in spring and 

 summer, is just the right combination of conditions 

 attained for developing tke dreaded tornado. The 



♦ M. W. Harrington. " .Abont the Weather," p. 164. .(New York. i8qo.) 

 •■> Clevehnd Ablw, "Tornado Fr^nuency per Unit Area." AMnt/Uy 

 Weather Review, vol. xxv., p. 250. (Washington, D.C., June, 1897.) 



