June 15, 1 888.] 



SCIENTIFIC NE\VS. 



561 



WHIRLWINDS. 



MH. GILBERT, Professor at the Colbert Municipal 

 School, has been fortunate enough to observe 

 near at hand a whirlwind or " land-spout," and he has 

 sent an account of the phenomenon to La Natia-e, accom- 

 panied by very good sketches, which we have obtained 

 permission to reproduce. 



On Sunday, May 13th of the present year, about 



Figs, i axd 2. 



half-past three in the afternoon, the author was walk- 

 ing with some members of his family on the field of 

 manoeuvres at Vincennes, along the so-called Route de 

 la Pyramide, at the junction of the roads leading to the 

 farm and the pheasantry. The heat was overpowering 

 (here in England it was the first genial day of the 

 season), the sky very pure, and the air absolutely calm. 



Figs. 3 and 4. 



On arriving at five or six metres from the spot marked 

 A on the sketch (Figs, i and 2), he heard a strange and 

 very distinct sound, like that which would be made by 

 spinning a colossal top. This was the more strange as 

 there was no apparent cause ; the atmosphere remained 

 clear and calm, and the country, which is quite flat, pre- 

 sented nothing uncommon. He now perceived at A a 

 rotatory movement of great violence ; the road is very 

 dusty, and the dust and fragments of all sorts seemed car- 



ried along in a very rapid revolving movement (Fig. i)- 

 The whirlwind then took a definite form, that of a large 

 funnel placed in its ordinary position. The sand carried 

 along by the rotatory movement expanded by degrees as 

 it ascended on the circumference of the whirlwind. 



The apparent size of the "land-spout" increased 

 rapidly by the constant afQux of dust, which finally 

 collected at the height of 20 or 25 metres, forming an 

 opaque cloud of a globular form. 



But the whirlwind, including the globular cloud, was 

 also actuated by a general movement of translation, far 

 more slow than the rotatory motion. The column moved 

 as a whole without becoming bent, which may be due to 

 the perfect stillness of the atmosphere, or to the slow- 

 ness of the translatory movement. 



The first dust column, represented by Fig. 2, lasted 

 at most for three or four minutes. On arriving at B the 

 point began to oscillate in a vertical direction, to dance, 

 if we may use the expression. Finally it rose up from 

 the ground, and the whole disappeared. At the upper 

 part there remained nothing but a vague cloudiness 

 which quickly vanished. In Fig. 2 the arrow f i gives 

 the direction of the translatory movement; f2 shows 

 the direction of rotation. 



A few moments afterwards a second point began to 

 appear at D (Fig. 3), a column was formed smaller than 

 the former, and travelled quickly along the track D E, 

 but its career was very brief. This was not the case 

 with the third and last column, which took its rise nearly 

 at the same spot A, and recommenced a series of move- 

 ments similar to those already described. The globular 

 cloud was less distinctly visible. The phenomenon, 

 however, was more durable ; it described a path, A C 

 (Fig. 3) of at least 100 metres in length, and presented 

 towards the end of its career — five or six minutes — a 

 remarkable segmentation. On arriving at C the point 

 began to dance ; then, suddenly, it gave place to five or 

 six smaller points, which arranged themselves in a circle 

 of some metres in diameter. Each of these points re- 

 volved upon itself in the same direction as the original 

 point. Further, they were all animated with a circular 

 movement along the circumference on which they are 

 distributed. The general rectilinear movement of trans- 

 lation had ceased. After a few seconds the points grew 

 weaker, danced, rose up, and disappeared. 



The author attempted to ascertain approximately the 

 temperature of the ground where these phenom.ena first 

 made their appearance. He applied the back of his 

 hand to the ground and felt a slight sensation of cold. 

 He then examined the furrow (A B, Fig. 4) traced by the 

 point of the first whirlwind or dust-spout. The soil 

 seemed confusedly hollowed for a uniform breadth of a 

 few centimetres, and sharply defined. But beyond this 

 furrow there was no trace of any converging movement 

 of the dust such as might result from an inrush towards 

 the axis of the whirlwind. Lastly, it is said that the 

 general state of the atmosphere and its equilibrium did 

 not seem affected by these phenomena. 



We must, however, not forget that a few hours later 

 there occurred, in the South of England at least, a sudden 

 atmospheric change. On Sunday, May 13th, the weather 

 near London had been much like that experienced at 

 Vincennes. Early in the morning of Monday, 14th, the 

 wind turned to the north-east with a great fall in the 

 temperature. La Nature regrets that M. Gilbert did not 

 approach the column and try to feel if there was any 

 ascending or descending current of air. 



