io6 



NATURE 



{May 31, 1888 



M. Weyher next proceeds to discuss the motions which 

 should theoretically occur in an air-whirl. These are 

 shown in vertical section in Fig. 2. 



In the annular region bordering the inner rarefied 

 space, and represented by Aacc f b B D d, the air is 

 assumed to be rendered denser than the normal by the 

 centrifugal force of gyration, and according to M. 

 Weyher it is by the descent of this denser air upon the 

 depression caused by the air below rushing up to fill the 

 central area, that the rotation system propagates itself 

 from above towards the earth. 



We do not think this explanation is either correct or 

 necessary. It is contrary to the physical theory that 

 there should be a sheath of dense air surrounding the 

 rarefied region, and, apart from this, friction, and the 

 transference of air up the axis from its lower end amply 

 account for the downward propagation. 



The most interesting of M. Weyher's experiments are 

 those in which he artificially produces the phenomena of 

 the waterspout. By means of a rotating tourniquet placed 

 over cold water, an aerial eddy is caused which draws up 

 the water, in the form of a spout composed of drops, to a 

 considerable height ; but when the water is heated, a 

 clearly-defined condensed-vapour-, or, as it is popularly 



Fig. 2. 



termed, water-spout, makes its appearance, like that 

 shown in Fig. 3, which represents a form of the 

 apparatus suitable for a chamber experiment. 1 



With from 1500 to 2000 rotations per minute, the 

 vapour from the heated water is found to condense itself 

 into a visible sheath enveloping a clearly-defined and 

 rarefied central nucleus, conical, and tapering downwards. 

 The diameter of the sheath is from f inch to 1 inch. 

 Besides this vapour-spout, water-drops are carried up, as 

 in natural marine spouts, until they are thrown 'out 

 beyond the influence of the upward current. 



Other features of spouts are then imitated, particularly 

 what is called the herisson, which appears to be identical 

 with what the French sailors call the buisson, or bush- 

 like ploughing up of the sea, which occurs at their bases, 

 both before and during the period of complete formation! 

 This is effected by placing twenty or thirty small air- 

 balloons in the place of the water, underneath the 

 tourniquet. These are then seen to rise up a short 



r u F ° r l i.u Se desi r in g t0 re P eat the experiment the dimensions are as 

 follows. The tourmqu-.t is made of tin from 5 to 6 inches in diameter bv 1 

 to 1* inch in height 1 here are from 10 to 12 rectangular fans 1 inch bv 

 i inch. The vessel holdmg the water is placed 31 to 39 inches froir the 

 tourniquet, and is from 7 inches to 1 foot in diameter by r£ to 2 inches deeo 

 The hemispherical continuation of the vessel, to keep off local air-currents 

 which disturb the continuity of the spout, is 3 feet in diameter 



distance, and fall back in graceful interlacing elliptical 

 curves. The entire motion throughout the hc'risson, as 

 well as the whole system, is further studied by placing 

 underneath the tourniquet a quantity of oatmeal in a 

 glass vessel, and observing its motion by means of eye- 

 pieces fitted into the top of the vessel. The motions are 

 thus seen to be precisely the same as those theoretically 

 inferred, and when the rotation is stopped, the ascending 

 spires of the currents at the lower end, are found engraven 

 in lines on the finer particles, which, in obedience to these 

 currents, lie in a conical heap round the vertical axis of 

 the whirl. 



Several other experiments are made with cotton-wool 

 and smoke, each of which exhibits some special feature 

 characterizing the spouts of Nature. 



The pressure and temperature conditions in different 

 parts of the area are next investigated. 



Fig. 3. 



By means of a manometer, it is found that the rarefac- 

 tion at the centre of the rotating tourniquet is transmitted 

 almost unaltered in intensity (probably proportionally 

 diminished in area) to the centre of the whirl on the 

 surface, while the thermometer at the same point, at first 

 shows a fall and then a rise of temperature, the latter 

 evidently due to the friction of the rapidly moving air 

 against the surface. 



The analogous phenomenon of a cyclone is very fairly 

 imitated by the apparatus shown in the accompanying 

 diagram (Fig. 4), consisting of a large tourniquet placed 

 over a table covered with a number of pins mounted with 

 movable threads of red wool. The tourniquet is arranged 

 so as to be capable of'translation as well as rotation. At 

 the centre, the table is pierced with a small hole at D, 

 communicating by means of a caoutchouc tube with a 

 manometer, which thus registers the changes of pressure 



