Februaky 8, 1889.] 



SCIENCE. 



lOS 



to render more perfect and more easily accessible, at home and 

 abroad, our noble language and our glorious literature. 



Now, I have not only told you the subject that most interests 

 me, but explained the origin of my interest in it, and endeavored to 

 excite your interest in it also. Pardon so much use of the first 

 person. The narrative could not be cast in another mould. 



SOMETHING ABOUT TORNADOES." 

 What are the local signs of conditions favorable to the forma- 

 tion of tornadoes? I. The prevalence of southerly winds, with a 

 gradual but continued increase of heat and moisture ; 2. A sultry 

 and extremely oppressive condition of the atmosphere, which is 

 sometimes characterized as " sticky," or so quiet as to call forth 

 the remark that " there is not a breath of air stirring ; " 3. The 

 form, motion, character of development, and place of formation, of 

 clouds. The sudden appearance of ominous clouds, first in the 

 south-west, and then almost immediately in the north-west and 

 north, is sufficient to attract the attention of the most casual ob- 

 server. In nearly all instances, these premonitory clouds are unlike 

 the ordinary formation which signifies rain, and perhaps a thunder- 

 storm. If the clouds are light, they resemble smoke rising from a 

 burning building ; if dark, they present a deep greenish hue, which 

 appears to increase in intensity as the storm advances. Sometimes 

 these dark clouds appear as densely black masses of smoke, rolling 

 upward from the chimney of an engine. The motions of the clouds 

 are peculiar, in that they appear to be rushing from every quarter 

 towards a common centre, making the incipient stages of a gyra- 

 tory motion in the cloud region. The next step in the progress of 

 development is the appearance of a small darting tongue of cloud, 

 which suddenly proceeds downward from the centre of commotion, 

 and ultimately reaches the earth as the full-fledged funnel-shaped 

 tornado-cloud. 



This brings us to consider what are the signs of its approach. 

 The tornado-cloud is, of course, not visible from all directions while 

 sweeping the earth. The limit of vision is necessarily greater in 

 some cases than in others, depending upon the topography of the 

 intervening country. Where the funnel-cloud cannot be seen, its 

 existence can readily be distinguished by the peculiar roaring noise 

 which is likened to the rumbling of distant thunder, or the ap- 

 proach of a heavy train of cars. The noise is said to resemble the 

 " sighing of the wind through the forest." As the storm approaches 

 nearer, the sound increases in intensity until the final crash of the 

 elements, which comes with the suddenness of an explosion. The 

 noise is sufficiently peculiar and distinct to create an alarm, and, as a 

 means of warning, must not be ignored. A few moments before the 

 assault there is a death-like stillness in the air. The observer's 

 eye catches the absence of any movement in the leaves upon the 

 trees, which a moment before danced in a gentle wind. The omi- 

 nous silence portends grave results, and requires that no time be 

 lost m seeking the most perfect means of safety. 



The form of the tornado-cloud in individual cases is somewhat 

 variable ; but it always tapers from the top downward, the smaller 

 end being nearest the earth. It is described by eye-witnesses as 

 resembling an " elephant's trunk, '' " balloon-shaped, " " egg- 

 shaped," " basket-shaped," etc. While passing along its path, the 

 cloud is characterized by four distinct motions, which may be des- 

 ignated as (i) the " progressive motion," generally from some point 

 in the south-west quadrant to some point in the north-east quad- 

 rant ; (2) the " whirling or gyratory motion," always from right to 

 left, or contrary to the movements of the hands of a watch with 

 the face upward ; (3) the " curvilinear motion," where frequently 

 the cloud rises from the earth, breaking the continuity of its path 

 for a distance of several rods to as many miles, then returns sud- 

 denly to the earth with renewed energy, continuing its violence as 

 before; and (4) the "oscillatory motion," a swaying from side to 

 side of the central line of cloud movement. (This motion is some- 

 times quite sudden, but generally it is a moderately slow motion, 

 and easily identified : the regularity of it depends upon the fre- 

 quency and severity of the indraughts of air from the south side of 

 the storm's path into the vortex of the cloud). 



' Portion of a paper read before the National Geographic Society of Washington, 

 Nov. 16, 188S, by J. P. Finley, continued from Science, No. 313. 



It is important here to state that the south or right-hand side of 

 the tornado is the most dangerous part of the storm, as it is also in 

 the case of the cyclone. On this side the inflow of air toward the 

 vortex coincides both with the progressive motion of the tornado and 

 with the general easterly movement of the " low," thereby increas- 

 ing the velocity of the southerly currents. On the north or left- 

 hand side of the tornado the incurving winds oppose the direction 

 of the currents advancing to the vorlex, and therefore the force of 

 the wind is very much less on this side: it is therefore the safest 

 side of the storm. The tornado-cloud is swept along by the gen- 

 eral currents prevailing in the south-east quadrant of the "low," 

 and whatever may suddenly affect these movements will also ex- 

 tend its influence to the tornado-cloud, and thus increase or dimin- 

 ish its gyrations, sometimes to the extent of withdrawing the cloud 

 entirely from the earth. The tornado continues in the full mani- 

 festation of its power until the force arising from the gyrations is 

 no longer adequate to keep the pressure and temperature in the 

 vortex low enough to cause condensation ; and therefore the lower 

 part of the cloud vanishes first, the decrease of power continuing 

 until nothing appears on the funnel, and a dark, irregular mass of 

 cloud marks the spot from which the spout had previously de- 

 pended. 



" Windfalls " are the tracks of tornadoes through forests, as 

 shown by the prostrated and confused masses of timber. In many 

 cases there remain but the skeletons of these ruins, and their loca- 

 tion is known only to Indians, trappers, hunters, and surveyors. 

 There is not a State east of the Rocky Mountains that has escaped 

 these serrated tracks through its forests, and the record of their 

 occurrence will in many cases be found upon the plats of the early 

 State surveys. Windfalls both of recent and of very early date are 

 still to be found in the forests east of the Mississippi. The late 

 Professor I. A. Lapham of Milwaukee, Wis., attached to the signal 

 corps in 1870-72, made, in the latter year, a very exhaustive and 

 interesting report on the windfalls of Wisconsin. As the result of 

 a very careful examination of the plats of public surveys made 

 within the State, he discovered and marked upon a chart the loca- 

 tion and approximate length of path of three hundred and sixty 

 windfalls or tornadoes. 



The successful protection of life depends upon the position and 

 surroundings of the observer on the approach of the tornado, the 

 character of motion possessed by the tornado-cloud at the time, the 

 width of the path of the storm, and the velocity with which it is 

 moving. 



The following precautions have been determined upon as the re- 

 sult of careful investigation, observation, and experience: I. The 

 south side is the dangerous portion of the tornado, the north side is 

 the safe portion. 2. In the open country, never undertake to es- 

 cape from a tornado-cloud without first making sure of the points 

 of the compass, and that the direction which you propose to take 

 is in a line at right angles to the path of the advancing cloud. 3. 

 If the cloud is moving to the north-east, then the line of escape is 

 to the north-west; if to the east, then to the north. Stand facing 

 the advancing cloud in the direct line of its approach, and the safe 

 side is always to the right. 4. To make escape certain, the torna- 

 do-cloud should be about three-fourths of a mile distant. This 

 gives the observer a momentary chance to ascertain the character 

 of motion it possesses, the velocity of progression, the width of the 

 path, and the points of the compass. These estimates must of 

 necessity be approximate, but can be made sufficiently accurate to- 

 be depended upon. At a greater distance than three-fourths of a. 

 mile, it would be difficult, in most cases, for the observer to obtain 

 this information with any degree of satisfaction, unless the atmos- 

 phere was clear, and the cloud advancing over the open prairie. 



A frame building is safer than one built of brick or stone. The 

 former is more elastic, and holds together longer. The latter goes 

 down in the first crash, and the debris is whirled into a heap in the 

 centre of the foundation. This is especially the case where a brick 

 or stone building stands alone. In a block of such buildings, one 

 structure supports another, and there is not quite so much danger 

 of entire destruction. In any event, however, the brick or stone 

 building is the most dangerous, because it so readily crumbles and 

 separates into falling masses, that the inmates are never safe froiiii 

 injury. 



