an early drawing and description of a tornado

An Early Drawing and Description of a TornadoAuthor(s): John LeighlySource: Isis, Vol. 65, No. 4 (Dec., 1974), pp. 474-486Published by: The University of Chicago Press on behalf of The History of Science SocietyStable URL: http://www.jstor.org/stable/229336 .

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An Early Drawing and

Description of a Tornado

By John Leighly*

To A GREATER EXTENT THAN IS TRUE of most terrestrial phenomena the investigation of tornadoes depends on observation from a distance,

on what in current jargon is called "remote sensing." Instrumental measurements near the centers of tornadoes are precluded by their destructive power, which no instrumental installation can withstand. Early in the history of the systematic study of North American tornadoes, John Park Finley (1854-1943), the most assiduous investigator of these windstorms in the nineteenth century, described the conditions under which a tornado that traversed the northwestern corner of Missouri on May 29, 1879, was observed:

The opportunities for making quiet and reliable observations upon the atmospheric conditions of the approaching storm were much better when the observer was removed a mile or so from the storm's path than when he was within the immediate influence of the furious monster, as under the latter condition he would be compelled to seek a place of safety for his life and property, and could not thereby observe the storm's effect with accuracy.1

The most valuable products of observation of tornadoes from a safe distance have been pictorial records. The official meteorological service of the United States, from 1870 to 1890 a part of the Signal Service of the Army, recognized from the beginning of its work on tornadoes the importance of pictorial representations. Its instructions to observers urged them to obtain "photographs, sketches, or printed cuts representing the tornado cloud or some evidence of its destructive power."2 Such photographs seem, however, to have accumulated only slowly. In his book Tornadoes (1887) Finley was able to reproduce only three photographs of tornado clouds; almost all of his illustrations are reproduc- tions of drawings, "most of them by persons not artists."3

Since the time when Finley was making his early investigations photography has made the appearance of the tornado cloud familiar, even to the casual reader of newspapers, and has made possible the use of photogrammetric

Received Nov. 1972: revised/accepted Oct. 1973.

* Department of Geography, University of California, Berkeley, California 94720.

'J. P. Finley, "Report on the Tornadoes of May 29 and 30, 1879, in Kansas, Nebraska,

Missouri, and Iowa," Professional Papers of the Signal Service, 1881, No. 4: 94.

2Signal Service, U.S.A., Tornado Circular, N.S., No. I (Washington, D.C., n. d.), p. 10.

'John P. Finley, Tornadoes (New York: The Insurance Monitor, 1887), p. 21 n.

474



DESCRIPTION OF A TORNADO 475

methods for measuring tornado clouds and of motion pictures for measuring the movements of the air in them.4 "Imaging" by wavelengths of radiation outside the visible spectrum has been applied: radar has revealed vortical circulations aloft within clouds,5 and a narrow band of infrared radiation emitted by water vapor, recorded with instruments carried by artificial satellites, has been used to identify the high tops of tornado vortices.6 These applications of technology are but extensions of the long-established practice of recording the visible features of tornadoes and their close relatives, waterspouts, by means of drawings.

EARLY DRAWINGS OF TORNADO CLOUDS

The primary purpose of this article is to make known a hitherto unpublished drawing, and the accompanying description, of a tornado observed in the East Baltic region in June 1795; the drawing is reproduced in Figure 1. Beyond its significance in the chronology of the depiction of tornadoes, Figure 1 is of interest in that it represents a form of tornado cloud different from that of the bell of a brass musical instrument and the straight tube continuous with it which has been accepted as its characteristic form and has given rise to the partly internationalized French term trombe.

Very few drawings of tornado clouds were published before the year 1800. David Ludlum has collected accounts of a number of tornadoes observed in eastern North America before that date, none of which seems to have been accompanied by a drawing, though some record the typical form of the tornado cloud.7 Alfred Wegener's Wind- und Wasserhosen in Europa is the best source of information concerning early pictorial representations of tornadoes and waterspouts observed in Europe and over its neighboring seas.8 In his list of 258 examples of these phenomena, which constitutes his Chapter 3, Wegener distinguishes by asterisks those whose published descriptions are accompanied by illustrations. His list is certainly not exhaustive, but he examined thoroughly the literature that is readily accessible and some that is obscure. He marks by asterisks eight of his examples recorded before the year 1800. Five of these are certainly waterspouts. Of the three remaining, one-reported from Topsham in Devon as occurring on August 7, 1694-caused some damage

4E.g., Robert G. Beebe, "The Life Cycle of the Dallas Tornado," in "The Tornadoes at Dallas, Tex., April 2, 1957," U.S. Weather Bureau, Research Paper No. 41, 1960, pp. 3-11; Walter H. Hoecker, Jr., "The Dimensions and Rotational Character of the Tornadoes and their Cloud System," ibid., pp. 53-1 1; Tetsuye Fujita, "A Detailed Analysis of the Fargo Tornado of June 20, 1957," U.S. Weather Bureau, Research Paper No. 42, 1960.

5 E.g., Louis J. Battan, Radar Meteorology (Chicago: University of Chicago Press, 1959),

pp. 110-116. 6Lewis J. Allison, Joseph Steranka, G. Thomas

Sherrix, and Ernest Helsenrath, "Meteorological Applications of the Nimbus 4 Temperature- Humidity Infrared Radiometer, 6.7 Micron Channel Data," Bulletin of the American Meteorol- ogical Society, 1972, 53:526-535.

7David M. Ludlum, Early American Tornadoes 1586-1870 (Boston: American Meteorological Society, 1970), pp. 3-19, 37-42, 73-78.

8Alfred Wegener, Wind- und Wasserhosen in Europa (Braunschweig: Friedr. Vieweg, 1917).



476 JOHN LEIGHLY

on land and so may possibly be classified as a tornado.9 The illustration accompanying the account of this storm is wholly unconvincing. Mr. Zachary Mayne, who reported it, did not see it himself but made his drawing from verbal descriptions provided by eyewitnesses. One of the other two, A14 of Wegener's list, observed in Mecklenburg on June 29, 1764, was represented, he says, by "a poor picture of the tornado printed on the title page" of the pamphlet in which it was described. The best of the older illustrations Wegener cites is his remaining one, in fact the oldest: it represents a tornado observed at Augsburg on July 2, 1597. The record of this storm is a contemporary broadsheet illustrated by. a woodcut, which was handsomely reproduced in facsimile by Gustav Hellmann in 1899.10 It shows an entirely plausible tornado funnel, hanging from a cloud cover, against the background of the city. Wegener missed seeing an even better illustration, a series of small drawings representing several stages in the growth and decay of a tornado observed near The Hague in July 1751. In accuracy of observation this series surpasses all of the older drawings he cites. "

Waterspouts are described and illustrated in the older literature more abundantly than tornadoes. The best published illustrations of waterspouts older than the drawing reproduced here as Figure 1 are those accompanying descriptions of spouts observed from shore at Nice by one Michaud on April 12, 1780, and on January 6 and March 10, 1789.12

PROVENANCE OF FIGURE 1 AND THE ACCOMPANYING DESCRIPTION

Forty-odd years ago, during the winter of 1929-1930, I had occasion to spend a good deal of time reading in the municipal library of Riga, Latvia. In addition to its printed materials, this library, which had its origin in a collection of books assembled from monastic institutions at the time of the Reformation in the sixteenth century, possessed many manuscripts; it was one of the principal repositories of source materials for the history of the East

9"Mr. Zachary Mayne's Letter, 1694. Concern- ing a Spout of Water that happened at Topsham on the River between the Sea and Exeter," Philosophical Transactions of the Royal Society, 1698, 19:28-31, Fig. 3.

"'"Schr6ckliche newe Zeytung auss Augspurg . . .,' in Gustav Hellmann, "Wetterprognosen und Wetterberichte des XV. und XVI. Jahrhun- derts," Neudrucke von Schriften und Karten iiber Meteorologie und Erdmagnetismus, No. 12 (Berlin: A. Asher & Co., 1899). Wegener reproduces the illustration in his Wind- und Wasserhosen as Fig. 68, p. 227.

"'J. F. Dryfhout, "Nauuwkeurige be- schouwinge van een hoos, benevens een onder- soek, hoe dezelve geboren worden en werken

Verhandelingen uitgegeven door de Hol- landsche Maatschappij der Wetenschappen te Haar- lem, 1757, 3:321-377, Plts. I, II.

12 Michaud, "Observation d'une trombe de mer faite a Nice de Provence en 1780," Observations sur la Physique . . . (ed. [Jean] Rozier), 1787, 30:284-287, Plt. ILL; "Observations sur les trombes de mer vues de Nice en 1789, le 6 janvier et le 19 mars," Memoires de l'Acadimie Royale des Sciences de Turin, 1790, 4, Memoires presentes a I'Academie: 3-22, Plt. XI. The latter paper was published in German translation as "Beo- bachtungen einiger Wasserhosen die am 6ten Januar und am 19ten Marz 1789 zu Nizza gesehen wurden," Annalen der Physik, 1801, 7:49-69, Plts. I, LII The re-engraved plates in this edition are smaller than the original ones published at Turin, and each is divided into two figures. I am unable to find the forename of this Michaud; he is identified in the list of correspondents of the Turin Academy as "ing&. nieur au port de Nice."




Baltic region. None of its manuscript materials was more frequently used by scholars than a set of ten folio volumes of collectanea written, copied, and drawn by Johann Christoph Brotze (1742-1823), the title of which-Sammlung verschiedener livlandischen Monumente, Prospekte, Miunzen und dgl.-sufficiently describes its miscellaneous character. According to Brotze's own statement, he worked on this collection "for 47 years, from 1771 to 1818." Besides copies of public and private documents of all sorts, it contained, as its title suggests, many drawings: of scenes from nature, of coins and seals, and copies of maps. Brotze was a native of Silesia who came to Riga as a young man in the capacity of a private tutor. He soon became a teacher in the municipal Lyceum (later Gymnasium), in which position he served, much of the time as acting rector, until he retired in 1815.'3 His outstanding accomplishments as a draftsman and penman contributed greatly to the value and attractiveness of his collectanea.

My immediate interest in Brotze's collection was directed toward other matters, but I was impressed when in his tenth volume (pp. 151-152) I came upon a description of a tornado observed northeast of Riga on June 22 (new style; Brotze recorded the date according to old style as June 10), 1795, accompanied by a drawing in pen and wash. I transcribed the description and had a photograph made of the drawing. It is this photograph, not so good as one might wish, reduced from the original drawing by about one-third, that is reproduced here as Figure 1.

The municipal library in Riga was housed, from 1909 on, in an upper floor of the city hall, a graceful rococo building from the middle of the eighteenth century. This building, along with other architectural monuments in Riga, was completely destroyed in the shelling of the city by the Russians when they re-occupied the Baltic region in 1944, and with it, so far as I am aware, were destroyed the contents of the library. It is scarcely possible that anything remains of Brotze's description and drawing of this tornado except my tran- scription and photograph.

BROTZE'S DRAWING AND DESCRIPTION

Brotze recorded that he was indebted for his description and the accompanying drawing to Baron W. F. von Ungern-Sternberg. Wilhelm Friedrich, Baron von Ungern-Sternberg (1750-1832), was a member of one of the old families of the Baltic nobility, a prominent jurist, active in public affairs of the city and province. Brotze's relations with him included at least one other collabo- ration, in the acquisition for an archive in Riga of copies of documents in the archive of the Teutonic Order in K6nigsberg (now Kaliningrad) relating to medieval Livonia.

The drawing in Brotze's collection was, however, obviously from his own

13 Bernhard Hollander, "Dr. Johann Chris- toph Brotze als Padagog und Geschichts- forscher," Mitteilungen aus der liivlndischen Ge- schichte, 1924-1926, 23:268-295, gives an ac-

count of Brotze's career and lists of his manuscript collectanea (which include far more than the Sammiung cited here), of his published writings, and of published writings about him.



478 JOHN LEIGHLY

. Jy/v/ i{zZCSt SJ~~~~'. "

-- t1~~~~~~u -s 71 1

~I~((jf6fh.i.na MTri4j von I6Werdf4kt r

Xi w+ S7.

if 4 itt 'Itnc Ut i Ijpl' i fichfc

Figure 1. J. C. Brotze's drawing of the east Baltic torado of

June 22, 1795.

hand; it was executed in his familiar manner and embellished with his customary calligraphy. He must have worked it up from the drawing he credits to Ungern-Sternberg, which, one may surmise, was less skillfully done than one Brotze himself would have made from direct observation. The drawing shows conventionalized lightning flashes proceeding from the pendent tornado cloud and a heavy fall of hail, which must be doubted. Lightning and hail usually accompany tornadoes, but they are associated with the general cloud system of which the tornado cloud is a part, not with the tornado cloud itself. Brotze's verbal description calls the tornado cloud [eine] ungeheure grosse Hagelwolke,




die Blitze von sich schoss; these words may have led him to add the hail and lightning to the tornado cloud when he was making his version of the drawing.

In the confusion of a violent storm an uncritical observer might well lump together all of the destructive attributes of the storm. Examples of such confusion appear in early reports of American tornadoes. One might also doubt the exaggeratedly mammate forms of the parent cloud; but J. F. Dryfhout (in the article cited in note I 1) describes the parent cloud of his tornado as "composed of a great number of smaller cloudlets, resembling round balls," which exhibited complicated motions among themselves, moving into and out of the body of the cloud. At least in Dryfhout's case this interpretation of the violent agitation seen in the clouds associated with tornadoes rested on a conception of clouds as bodies distinct from the air in which they float, not merely as parts of the atmosphere rendered visible by the local condensation of water vapor in the air. Perhaps some similar misconception lurks behind the mammate cloud forms in Brotze's drawing. What remains after all the dubious features of the drawing are discounted, however, is a pendent tornado cloud of a distinctive shape which, as will appear later, can be placed within the range of forms recorded by photography in more recent times.

The drawing bears two inscriptions: above it is the Latin title Typho terrestris and below it a legend in German that reads, in translation, "A waterspout, which on June 10, 1795, accompanied by large hail and lightning, completely devastated a path 160 versts in length and two versts wide within 4 to 5 hours." (In such rough estimates 1 verst may be taken as equivalent to 1 kilometer.) The text of Brotze's description does not wholly justify his expression gdnzlich verwiistete. It does not give evidence of total devastation everywhere but rather of destruction and damage over a long path, more severe in some places than in others. In Figure 2 I have drawn, from Brotze's description, the path followed by the storm.

The following paragraphs give pertinent excerpts from the description, translated and in part paraphrased. Interpolated remarks are enclosed in square brackets.

On the tenth of June, 1795, a storm accompanied by hail clouds and lightning moved inland from the Baltic Sea at Dunamunde. In and near Riga rolling thunder was heard from some distance and hail fell, which, however, did no noteworthy damage. From here the cloud moved farther northward, and exhibited the phenom- enon represented in the following drawing [here Fig. 1]. An enormous hail cloud, from which lightning flashed, descended through the whirlwind with a deafening roar and scream, its tip reaching the ground; it was bluish black in color and resembled an inverted cone. It was accompanied by an extremely violent wind, in constant rotation, which destroyed or damaged everything it encountered within a breadth of two and a length of one hundred sixty versts.

The description does not permit identification of the part of the path of the storm in which it behaved as a tornado except in the vicinity of Burtneck Lake, from which vicinity the account gives evidence of damage by destructive winds. In Figure 2 I have drawn in black that stretch within which the storm



480 JOHN LEIGHLY

24 26

) \ _~~ftk

PerAau Feillin (P~~irnu) 0(Vijndi Dforp

0(Tart

Burineckwl cake 'G~~~(Valka,Valga)

-of EWolmar

IVamiera)

iinainiindende

(D.tugarv

Path of hailstormn Riga Locus of tornado damage

Scale:

iookmn.

24~~~~~~~~~~~~2

Figure 2. The path of the East Baltic tornado of June 22, 1795, drawn from information given in J. C. Brotze's description.

displayed the indubitable qualities of a tornado; this is only 15 kilometers in length. (Cross marks on the path are drawn at intervals of 5 kilometers.) Effects of wind may be recognized in Brotze's account of damage done on the lands of Burtneck manor, situated on the southwest shore of the lake.

Here a herd of cattle was driven into the lake, where some drowned. People in the open who were unable to take shelter behind some large rocks on the shore of the lake were injured. A second account, to be cited later, adds that "itrees 12 to 15 inches in diameter were broken off or uprooted." The hail stones were of the size of pigeons' eggs. The description continues:

The hail cloud proceeded across the lake, where the hail, which had in part

the form of irregular masses of ice, completely devastated the fields of the parsonage



DESCRIPTIfON OF A TORNADO 481

[Burtneck church is east of the lake], of Durenhof estate and of the peasants round about, ruined the hay crop for this year, broke or split trees and shattered their bark, killed small live stock and poultry, and overthrew or damaged buildings.

A substantial part of this damage was obviously effected by wind. The remainder of the description recounts damage only by hail and traces

the further path of the storm. Beyond the vicinity of Burtneck Lake it moved "toward Rujen parish . . ., past Karkus [these localities are identified in Fig. 2 by their initials] . . . in the direction of Fellin. But from there it turned eastward toward Dorpat, and finally passed over Lake Peipus." The path as drawn in Figure 2 is certainly somewhat generalized but is commensurate in detail with the description.

Brotze added some instrumental observations made at Riga, which, however, contribute little to an understanding of the storm. He reported that on the day of the storm a thermometer exposed in the tower of the cathedral at an elevation of 170 feet (c. 52 meters) above sea level showed a temperature of -3? to - 4? Reaumur (-4? to -5? C.), while one exposed 4 feet above the ground (3 or 4 meters above sea level) showed at the same time between 180 and 190 R. (230 to 240 C.). So steep a lapse rate of temperature between these elevations is implausible; only the ground-level temperature is convincing. He reported further that "at noon the barometer stood at 24.80 inches; about 7 o'clock it had fallen to 24.73 inches; but at sunset [which would have been 8:40 to 8:45 P.M.], just about the time when the hail cloud had exhausted itself, it rose to the position it had about noon." This is the only passage in which Brotze mentioned the time of day when the storm occurred. That time was evidently the latter part of the afternoon, considering the "four or five hours" given in the legend of the drawing as the duration of the storm. The second report, mentioned earlier, states that the storm appeared southwest of Burtneck Lake at about 4 P.M.

The inch customarily used in the Russian empire, in which unit the barometric readings may be supposed to have been expressed, was the same as the English inch; Brotze's barometric readings thus indicate some fault in the barometer or in the reading of it, since the pressure he cites is much too low even for the center of an extratropical cyclone. The change in pressure he reported is informative, however. The pressure rose and then fell by 2 or 3 millibars, to use the modern unit of pressure. The lowest pressure was not observed when the storm was nearest Riga, but at 7 P.M., by which time it was somewhere toward the northeast, at a distance of 100 kilometers or more. This record of a pressure trough in the rear of a squall line-the linear feature of weather with which tornadoes are usually associated-is quite in accordance with experience in both Europe and North America. Beyond its immediate vicinity a tornado does not appreciably affect the distribution of atmospheric pressure.

One concluding comment in Brotze's account may be cited, more as an expression of conceptions regarding waterspouts popularly held at the time than as a characterization of this particular storm: "from all that has been said it may be concluded, with the greatest probability, that [the storm] was



482 JOHN LEIGHLY

a frozen waterspout." At that time many accepted the fallacious notion that the column of a waterspout consists of water raised in bulk from the surface of the sea or other water body. The word "frozen" undoubtedly alludes to the fall of irregular masses of ice as hail.

THE BALTIC TORNADO OF 1795 IN SCIENTIFIC LITERATURE

The tornado Brotze recorded has not gone completely unnoticed in scientific literature. In a paper published in 1873, which describes a hailstorm accompanied by two tornadoes that crossed southern Latvia in May 1872, G. Schweder included a two-page account of the storm of 1795.'4 Schweder had seen Brotze's record of this storm but does not mention the drawing. He had in addition another contemporary account of the storm from the records of Burtneck church, written by the pastor of the parish, J. H. Gulecke. Pastor Gulecke recorded details of wind damage done on both sides of Burtneck Lake, but especially in his immediate neighborhood, that were not included in Brotze's account. I have cited some of these details earlier. The two accounts "are in essential agreement," as Schweder says. He remarks that the storm of 1795 was the only one recorded that had been as destructive as the one of 1872 discussed in his paper.

When Alfred Wegener wrote his Wind- und Wasserhosen in Europa he had no information on tornadoes in the East Baltic region. Not long after that book was published, in the spring of 1918, Wegener visited Dorpat (Tartu), where his example and advice prompted Johannes Letzmann, a Privat-Dozent in the University of Dorpat, to investigate the record of whirling storms in the Baltic region. In his first examination of the record, published in 1920,15 Letzmann found seventeen tornadoes on twelve days to August 1918, the earliest being that of 1795, which he learned about from Schweder's paper of 1873. Letzmann wrote several additional papers on the subject in the following years, and in his final census, published in 1924,16 he counted twenty-two tornadoes to September 1922 and in addition eleven waterspouts seen near the seashore and over Lake Peipus; the storm of 1795 was still the earliest he found recorded. Not having seen Brotze's account, he did not know the drawing that accompanied it.

Letzmann's investigations established the East Baltic region as one in which, by European standards, tornadoes are relatively frequent. He identified a "Baltic tornado path" ("zone" would be a better term) extending northeastward from the Baltic coast in the vicinity of Memel (Klaipeda) to Lake Peipus, which approximates the northern part of the cyclone path Vb of the older European

14G. Schweder, "Der Hagelsturm des 10.(22.) Mai 1872," Arbeiten des Naturforscher-Vereins zu Riga, N.S., No. 5, 1873. The account of the storm of 1795 is on pp. 39-41.

1"J. Letzmann, "Tromben im ostbaltischen Gebiet," Sitzungsberichte der Naturforscher-Gesell-

schaft bei der Universitat Dorpat, 1 918-1 91 9, 1920, 26:7-46, Plts. I-VIII.

"6J. Letzmann, "Die Peipus-Trombe am 3. August 1922," Sitzungsber. Naturf.-Ges. Univ. Dorpat, 1923, 1924, 30:8-44; the list is on pp. 41-42.




synoptic meteorology. Letzmann's Baltic tornado path is probably an illusion grounded in incomplete observational data. Probably, if a long record of uniform observations over Europe were accessible, it would show a distribution of tornadoes not greatly different from what is seen in North America, but with a much lower frequency. That is to say, tornadoes have been observed in almost all parts of Europe, most of which move from between south and west toward the quadrant between north and east. Again, as in North America, they occur more frequently in some parts than in others, and Letzmann's work showed that the East Baltic region is one of these areas of relatively high frequency. Although Letzmann remarks, concerning the storm of 1795, that "information regarding this hailstorm is of course fragmentary and somewhat inexact," it is for its time quite well documented.

KNOWLEDGE OF TORNADOES IN THE EIGHTEENTH CENTURY

There is no evidence that those who left a record of the storm Brotze described had any acquaintance with the literature on whirling storms that was available in the last decade of the eighteenth century. As the title of his drawing of the tornado of 1795 Brotze used the Latin expression Typho terrestris. Scientific literature of the seventeenth and eighteenth centuries written in Latin customarily used the noun turbo instead of typho; the latter word seems to echo classical writings rather than to reflect contemporary Latin usage. But the adjective terrestris does reveal some knowledge of a distinction made in the literature between a waterspout, turbo aqueus, and a whirling storm on land, turbo terrestris, preserved among modern languages in the French terms trombe de mer and trombe de terre. The contradiction between the Latin superscription and the term Wasserhose Brotze used in his German legend below the drawing is additional evidence of his lack of familiarity with contemporary usage.

There was a substantial descriptive literature on whirling storms at the time when Brotze recorded the storm of 1795; only a few examples need to be cited here. Publications of scientific societies and academies contained numerous reports of observations of both waterspouts and tornadoes in the seventeenth and eighteenth centuries. Descriptions and illustrations, especially of waterspouts, were included in works dealing with the physical earth in general.17 The great Boscovich himself published in 1749 a dissertation on a tornado observed at Rome in that year, in which he not only described this particular storm but also reviewed similar storms previously described. He devoted even more space to a general discussion of the nature, causes, and mechanics of whirling storms.18

17E. g., Petrus van Musschenbroek, Introductio ad philosophiam naturalem (Patavii: Apud Joan- nem Maupre, 1768), Vol. II, pp. 517-521, Plt. LX; Torbern Bergman, Physisk beskrifning dfver jord-klotet (2nd ed., Uppsala, 1774), Vol. II, pp. 46-50, Plt. I. The illustrations of waterspouts (there is none of a tornado) in these works are

schematic.

18Ruggiero Giuseppe Boschovich [sic], Sopra il turbine che la notte tra gli XI, et XII Giugno del MDCCXLIX dannagio una gran parte di Roma (Rome: Appresso Niccol6 e Marco Paglianni, 1749).



484 JOHN LEIGHLY

Europeans treated with respect Benjamin Franklin's expositions of the behavior of atmospheric vortices, especially his explanation of the supposed aspiration of water upward at the center of a waterspout as resulting from the reduction of atmospheric pressure near the axis of the vortex. Franklin interpreted all such rotating storms as ultimately the product of the ascent of air heated at the earth's surface, such as is seen in dust whirls over warm land surfaces.'9

Johan Carl Wilcke (1732-1796), professor of experimental physics at Uppsala, investigated columns of liquid set in motion by a mechanical rotor as models of waterspouts and tornadoes.20 In discussing his experiments he came close to discovering the principle of hollow and multiple tubes in waterspouts elucidated in our own time.2' He recognized, as did Franklin, that the essential motion in rotating storms is ascent, from which both convergence and rotation follow. But the concepts advanced in scientific writings on whirling storms were evidently unknown to the educated citizens of Riga in the 1790s.

BROTZE'S DRAWING IN THE PERSPECTIVE OF TORNADO INVESTIGATIONS

There is a discrepancy between Brotze's verbal description of the form of his tornado cloud and his drawing. He described the visible part of the vortex as forming "an inverted cone" (einen umgekehrten Kegel), whereas the object represented in Figure 1 would be more accurately characterized as a pendent paraboloid at the lower end of which is a much slenderer, tapering, and curved tail-like appendage. The description and the drawing must have been based on observations made at different stages in the duration of the storm or by different persons. All detailed descriptions of tornado funnels record rapid changes in their form. Brotze's drawing is clearly not a schematic representation of an inverted cone, such as might be expected from his verbal description. It is not difficult, however, to place the form represented in his drawing within the context of the variety of forms of pendent tornado clouds.

In order to interpret Figure 1 it is necessary to distinguish two parts of the pendent cloud: one of larger diameter, which represents a depression of the general lower surface of the parent cloud with which the tornado is associated, called by American meteorologists the "tornado bulge"; the other is a slenderer part, or tube, most frequently tapering downward, the form of which varies, depending on the intensity of the vortex, from columnar to caudiform. This latter part changes rapidly in diameter, in length, and in the angle it makes with the horizontal. The two parts, though associated, evidently have different physical origins. The bulge would appear to be the

"9Benjamin Franklin, Experiments and Ob- servations on Electricity mode at Philadelphia in America (London: Printed for David Henry, 1769), pp. 191-196, 217-233, 356-359. David Ludlum summarizes Franklin's views in his Early American Tornadoes 1586-1870, pp. 138-142.

20Johan Carl Wilcke, "F6rsok til uplysning om

Lufthvirflar och Sky-drag," Kongl. Vetenshaps Akademiens nya handlingar, 1780, 1:1-18, Plt. I, 83-102, Plt. IV; 1782, 3:3-35; 1785, 6:290-307; 1786, 7:3-30.

21 Paul C. Kangieser, "A Physical Explanation of the Hollow Structure of Waterspouts," Monthly Weather Review, 1954, 82:147-152.




visible manifestation of a localized lowering of the condensation level of the parent cloud consequent upon the reduction by centrifugal force of atmospheric pressure within the vortex and the cooling associated with that reduction of pressure. It is the part of the tornado cloud that appears first and that lasts longest. The slenderer tubular or caudiform part of the cloud is formed in air drawn into the vortex from near the ground, which must be cooled more than the air at the base of the parent cloud in order to reach its condensation temperature. This lower condensation temperature is attained only at a pressure lower than that required to condense water vapor at the height of the base of the parent cloud and thus nearer the axis of the vortex.

The transition between these two parts of the tornado cloud is often gradual in the intense stages of the storm, so that the column or tube "fairs out" through the bulge into the parent cloud in the conventional trumpet form. The sharper contrast between the processes active at the two levels, conspicuous in Figure 1, is observed in the less intense phases at the beginning and near the end of the life cycle of the tornado, when the difference between these processes is more distinct than in the more violent phases of the cycle.

Figure 1 resembles most closely those forms observed near the end of the cycle. The only feature of the drawing that suggests the incipient stage is the small caudiform feature depending from a bulbous element of the parent cloud to the right of the tornado bulge. Multiple vortices are usually, though not exclusively, observed at the beginning of the life cycle of a tornado. Walter H. Hoecker, Jr., has proposed a general model of the evolution of the tornado cloud.22 Figure 1 is a fair match for either stage d or stage m of his evolutionary series of drawings. His d is an early stage, his m a terminal one. There are resemblances between Figure 1 and one of Michaud's excellent drawings, d of his Figure 4, which represents a waterspout observed offshore at Nice on March 19, 1789. Michaud's drawing shows a pendulous bulge below which a slender tube reaches down to the surface of the water. At this stage the spout was weakening, and it disappeared soon afterward.23 One of Dryfhout's drawings, Figure V of his Plate I, is an even better match. It shows the final stage of his tornado of July 1751, when it was drifting out to sea. Its slender column no longer extended to the water surface, and it was no longer straight but was bent into serpentine curves: "having lost its upright posture, [it] was blown upward toward the south, in the manner of a fluttering ribbon"; then it vanished completely. Dryfhout's description might be applied with little change to Brotze's drawing.

There is thus good reason to regard Figure 1 as an acceptable illustration of a tornado cloud in its terminal stage, when its rotational momentum was being dissipated by friction. After allowances are made for the unconvincing features of the drawing, it retains its value, not only as one of the very few

22Walter H. Hoecker, Jr., "History and Mea- surement of the Two Major Scottsbluff Torna- does of 27 June 1955," Bull. Am. Meteor. Soc., 1959, 40:117-133; the cycle is represented graphically in his Fig. 5, p. 130.

23Wegener reproduces this drawing from the German edition of Michaud's paper; it appears on the right side of Fig. 59, p. 218, of his Wind- und Wasserhosen.



486 JOHN LEIGHLY

early depictions of tornadoes, but also because it captures a tornado cloud in a stage of development different from the one conventionally taken as representative, a stage not otherwise recognized until abundant photographic evidence made possible a systematic examination of the varying forms such clouds assume.



an early drawing and description of a tornado

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