May 31, 1888] 



NATURE 



107 



as the supposed cyclone passes over it. On rotating the 

 tourniquet and passing it along over the table, the direc- 

 tions and positions of the threads are seen to indicate 

 not only the horizontal, but also the vertical components 

 of the winds thus produced, including the region of calm 

 in the centre, as well as the downward and outward 

 motion at the anticyclonic border. The variations of 

 pressure recorded by the manometer, when plotted out, 

 show a curve similar to that in a symmetrical cyclone, 

 including the rise of pressure at the border where the 

 motion is descending and outwards. 



Hail is then explained, as being caused by vapour 

 drawn up into the herisson of what M. Faye terms a trombe 

 inter nubaire, which descends from the upper regions as 

 far as the surface of the cloud, whence the hail proceeds. 

 The rest of the explanation, which mainly involves a 

 continual churning up and down of the frozen particles, 

 is similar to that given by Ferrel and Moller, except that 

 the hailstones impinging upon one another at the focus 

 of the herisson are supposed, by the heat thus engendered, 

 to aid in effecting the temporary melting of their surfaces 

 necessary to account for the concentric coats of snow and 

 ice they usually exhibit. 



M. Weyher's experiments do not, of course, fulfil all 

 the conditions which prevail in Nature, since in that case 



the rotation is doubtless kept up, after it has once been 

 started in the air at some distance above the surface, by 

 the upward movement along the axis, and the con- 

 sequent aspiration of the surrounding air into the area 

 of gyration. With this exception, however, there seems 

 little wanting. 



The position of the source from which the vapour is 

 drawn is not so important as might be thought, since the 

 vapour condensed in the natural waterspout is not the 

 cloud actually brought down to the surface, any more 

 than it is — except for the space of a few feet at its lower 

 extremity — the water bodily carried up, but is the result 

 of the condensation, by rarefaction, of vapour previously 

 contained invisibly, but certainly amply enough for the 

 purpose, right down to the earth's surface. In fact, the 

 origin of the vapour, being at the base, more nearly 

 imitates Nature than if it were only supplied above in the 

 form of a cloud. 



M. Weyher's experiments so far, therefore, bear out the 

 hypothesis that a system of rotating air-currents above 

 the earth's surface, causes tornadic, waterspout, and dust- 

 spout phenomena, by an aspiration towards, and a flow 

 up, its axis, and show that such a system can propagate 

 itself and its accompanying effects downwards without 

 assuming any downward component along the axis. 





Fig. 



The last part of the work is devoted to a description of 

 certain curious effects produced by rotating spherical 

 tourniquets. Fig. 5 shows a convenient form of the 

 apparatus, in which S represents a sphere made of eight 

 or ten circular fans, fixed on an axis passing through two 

 vertical disks whose function it is to keep off disturbing 

 currents, and also to concentrate the action. M is an air- 

 balloon, which, when the tourniquet is set in motion, is 

 found to revolve round it in the plane of its equator, and 

 be attracted instead of repelled. 



M. Weyher thus explains this, at first sight, paradoxical 

 motion. A rotating spherical ventilator draws in the air 

 chiefly at its poles, and expels it in the plane of the 

 equator, but, except in this plane, there is a general 

 motion of the air all round towards the ventilator. The 

 stream of air issuing from the ventilator in the plane of 

 the equator is divided by the balloon, and forms vortices, 

 which, together with the currents centrally directed on its 

 reverse side, tend to urge it towards the ventilator. 

 Whether this explanation be considered satisfactory or 

 not, the balloon certainly revolves like a satellite round 

 the ventilator. By means of floating gold-leaves, the 

 action of the ventilator is seen to cause two dissymmetrical 

 aerial whirls, whose inner gyrations commencing at some 

 distance from the generating sphere, run round the polar 



axis in opposite directions, and meet on the plane of 

 the equator. From thence the air jointly brought by 

 these inner helices is driven outwards, and returns by 

 similar helices, like the downward return-current of the 

 tornado, to the points at the extremities of the prolonged 

 polar axis. So far well, but we cannot quite admit the 

 validity of the manometer experiment by which, on p. 74, 

 the author attempts to show the existence of the aspira- 

 tion in the plane of the equator requisite to explain the 

 attraction it exerts on the air-balloon. The effect of 

 velocity in decreasing pressure, as exemplified by Hawks- 

 bee's famous experiment, would probably mask any other 

 vortical effects such as those sought by M. Weyher. 



It appears to be a recognized custom for an author, 

 after describing his experiments, to indulge in some pet 

 speculations, and even to make the orthodoxy of the 

 former an excuse for the frequently Utopian character of 

 the latter. 



M. Weyher certainly treats himself to an ample dessert 

 of this description in his concluding section, in which, 

 assuming the existence of a ponderable ether, the pheno- 

 mena of the tourbillon are by analogy transferred to 

 the solar system, which is supposed to be the herisson of 

 a whirl system reaching it from space, the sun being in 

 the focus, and in which the planets, by the mutual 



