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SCIENCE 



[N. S. Vol. LII. No. 1343 



slower north-northwestward-moving masses of 

 warmer air. At a moderate height condensation 

 took place in the moist, upthrust air, and as it 

 ascended at a lesser rate of cooling, due to the 

 liberation of the latent heat of condensation, it 

 probably was squeezed aloft at an increased rate 

 by the cold wind it was probably encountering. 

 Under such conditions intense vertical movement 

 accompanied by a rotary motion of small dimen- 

 sions makes a tornado. 



Tlie circumstanees surrounding the forma- 

 tion of the tornadoes of April 20 were some- 

 what different. In this case, there was a long, 

 oval-shaped low pressure area over the southern 

 part of the Mississippi valley. The storms oc- 

 curred in the morning at a time when the line 

 of vnnd-convergence was a considerable dis- 

 tance to the west of the line of tornado for- 

 mation. Therefore, it can not be said, as in 

 the previous case, that the mechanical effect 

 of the wind-shift line was operative. There is 

 another striking feature: All of these whirls 

 were formed along a north-south line which 

 lay about 30 miles west of the Mississippi-Ala- 

 bama line. The first occurred at Ingomar at 

 7:30 and followed a northeasterly course into 

 Tennessee where it continued by a series of 

 dips almost to the center of the state. The 

 second began about 40 miles south of the first, 

 near Bradley at 8:00 a.m. and moved north- 

 eastward, disappearing in northcentral Ala- 

 bama. The third began near 'Sew Deemer, at 

 8:30 A.M. and ended near Brownsboro, Ala- 

 bama. (This was the longest of the four 

 paths, and was marked by an almost continu- 

 ous swath of destruction for 150 miles.) The 

 fourth appeared at Bay Springs at 9:55 and 

 ended near the state line east of Meridian, hav- 

 ing passed within a mile of the "Weather Bu- 

 reau of^ce at that place. The significant facts 

 are, (1) that these tornadoes formed on a 

 nearly north-south line, and (2) that they 

 formed at almost equal intervals of time and 

 distance. The probable explanation is that 

 these formations resulted when an overrun- 

 ning layer of cold air arrived over a given 

 place, where other conditions were favorable, 

 increasing the vertical temperature gradient 

 to such a degree that there was immediate and 



intense convection. That this advancing front 

 was probably coming from the northwest is 

 shown by joining the positions of the torna- 

 does at any given time. The resulting line is 

 normal to the wind direction supposed to exist 

 aloft. 



According to Mr. J. H. Jaqua, the "Weather 

 Bureau meteorologist at Meridian, Mississippi, 

 the passage of the tornado at that place was 

 accompanied by almost total darkness. He 

 says: 



. . . The darkness between 10:30 and 10:39 a.m. 

 was as intense as would be common for a cloudy 

 moonless night at 9:30 or later, and though lights 

 were on in the business houses (but no street 

 lights were in operation), pedestrians could dis- 

 tinguish each other only with great difficulty. . . . 

 The pall of darkness was so unnatural that it was 

 extremely weird. . . . 



No account of tornadoes is complete without 

 the recital of some of the many " freaks " 

 which such storms are wont to perform. The 

 removal of feathers from chickens, the com- 

 plete destruction of houses, the clean sweeping 

 through deep forests, and the carrying of ob- 

 jects great distances, are examples frequently 

 recounted. Of the many curious pranks of 

 these storms, however, there are some which 

 are worthy of mention. Here are some ex- 

 cerpts from the numerous accounts in the 

 article cited above: 



An automobile locked in a garage was undam- 

 aged, although the garage was blown to splinters. 



Half a dozen glass jars of fruit were carried 100 

 yards by the winds and not damaged. (Bay 

 Springs, Miss.) 



A ear load of stone was whipped about like a 

 feather, and trees, one especially large oak, were 

 twisted from the roots as if they had been bits of 

 wire. (Florence, Ala.) 



There seemed to be two puffs of wind; one car- 

 ried things toward the west. In about a quarter 

 of a minute everything came back. I tried to keep 

 my family down on the floor. One of my boys 

 blew out of the house; then blew back. . . . (From 

 report of J. P. Sanderson, Newburg, Ala.) 



[The tornado] swept rapidly across the cove, 

 ... as it neared the mountain range and went 

 over it, leaving a path clear of any standing tim- 

 ber, houses, or fences. In going over the path of 



