6 ACCOUNT OF A TORNADO, 



upward, and centripetal, nowhere disappears, and at Mayfield was exhibited in 

 unequal strength. In some places the motion at right angles was strongly marked, 

 in others "well nigh masked." He says that, having discovered a true experimentum 

 cruds, for analyzing the phenomena of tornadoes by means of groups of crossed, 

 trees, " the peculiarities of a well-marked tornado can hardly escape detection," and 

 concludes that though the motion at right angles to a radius may sometimes be quite 

 small, compared with the centripetal motion, yet that it " can ever become mathe- 

 matically nothing, is infinitely improbable." To prove the rotation of the wind, 

 the Professor measured the bearings of seventy prostrate trees extending across the 

 track; he "did not take the bearings of all indiscriminately, because it was a hope- 

 less task, the prostrate trees being counted by thousands." He searched for trees 

 crossing each other, and found but one case on the right side of the track near the 

 middle ; but on the left side the phenomena were very different ; here was no diffi- 

 culty in finding crossed trees, and he measured few others. The Professor gives 

 the bearings of these, and the order in which they overlie each other. (See Silli- 

 man's Journal, XLIII, 285.) 



A reference to the phenomena of these tornadoes shows that there is a general 

 uniformity in their character, and that it is contrary to fact to say that the " trees, 

 amid all their variety of bearing, always point towards the centre of the path, or 

 a point occupied by the axis of the tornado," as affirmed by some; for out of forty 

 prostrations on the north side of the axis at New Haven, Olmstead gives twelve 

 exceptions of trees lying outwards from the centre; and on the north of the axis, 

 at Mayfield, Loomis gives at least twenty trees pointing directly outwards from the 

 centre, out of fifty prostrations ; and the like effects are exhibited at New Har- 

 mony, as shown in Fig. 2. 



It is improbable that any one can come to a right conclusion regarding the order 

 in which the wreck of a tornado lies, without plotting a. portion of it from instru- 

 mental survey. Knowing the tendency which exists in most minds to see chiefly 

 those facts which favor a preconceived hypothesis, it seems to me that to select a 

 few groups of trees out of thousands, would not afford sufficient evidence to others, 

 however satisfied one might be with the truthfulness of his illustrations. I there- 

 fore present the plot of a square mile of track on which some 7 or 8,000 prostrated 

 trees are represented in their relative positions,' with the hope that the means will 

 thus be furnished for more satisfactorily determining whether the "immediate 

 mechanical cause of devastation in tornadoes" be a spirally involuted rotating 

 moving column of air, or a vertical current at the centre of the tornado with a 

 horizontal conflux from surrounding space to the moving axis. 



To further this object, and to more readily compare the phenomena with the 

 hypotheses, I have appended diagrams, illustrating the rotating cylinder, and the 

 up-moving column, with prostrated trees, in accordance with these hypotheses 

 respectively. 



Fig. 5 of the map illustrates the rotating cylinder, which Kedfield theoretically 

 describes as follows : " The involuted lines or arrows represent the motion of the 

 wind at the bottom of the cylindrical vertical portion of the tornado. The motion 

 of a particle of air, as at a, quickens as it approaches the centre /, describing in its 



