Oct 7, 1875J 



NATURE 



499 



as this excess of temperature is felt at the same time over 

 a wide area, the lower stratum of air rises bodily, so to 

 speak, over the whole region. Now there is no reason 

 why the air should begin to ascend at one place rather 

 than another in the region where the air is perfectly 

 calm ; there will be then between the lowest aerial 

 stratum and the one immediately above it a sort of equi- 

 librium, but an equilibrium so essentially unstable that 

 the slightest accident, such as the striking of a light or 

 the flight of a bird, instantly destroys it. As soon as the 

 charm is broken at some point the lower air will there 

 ascend, and as it is charged with moisture it will continue 

 to rise in an ascending column to the higher regions of 

 the atmosphere. In rising, this air will leave a vacuum 

 below it, towards which will rush the air of a lower 

 stratum. This will in turn follow the first in its ascent, 

 and it is seen that gradually the air of this highly heated 

 lower stratum will flow from all sides with an accelerating 

 speed towards the pathway opened by the first ascendtti<^ 

 pufi of wind. As this propagation of the horizontal 

 movement extends wider and wider over the heated 

 stratum, the air which arrives at the place where ascend- 

 ing currents have set in will be of the temperature required 

 to keep up the indraught. Further, the vis viva of the 

 air currents about the narrow space where the equilibrium 

 was first disturbed will acquire a force capable of pro- 

 ducing, a short distance from the point towards which 

 they all converge, very considerable mechanical effects. 

 Then, if the whirlwind advances on the sea, its surface, 

 lashed on all hands by the converging winds, is thrown 

 into a state of ebullition ; the spray is drawn up in an 

 ascending column and whirled aloft, however slight may 

 be the spiral form assumed by the horizontal converging 

 currents. The air which rises so violently in the water- 

 spout will be thrust higher and higher, as we have just 

 seen, by the force constantly called into play by the con- 

 densation of the vapour into cloud and rain ; at length it 

 reaches the high regions of the atmosphere, where it 

 expands and swells into a dense cloud of enormous 

 dimensions. This, then, is the theory of aspiration. 



Before a physicist reasons in this way he ought to be 

 well assured beforehand that the facts are as he supposes ; 

 in other words, that waterspouts suck up by a vast upright 

 tube the air and the water of the lower strata. Otherwise 

 he would not fail to remark that if the equilibrium, emi- 

 nently unstable, which he assumes to be established, 

 comes to be destroyed at any point, it would be quickly 

 destroyed over the whole extent of the lower stratum, the 

 different parts of which would then rise freely, each in its 

 place successively, over the small space required for the 

 re-establishment of the equilibrium of the atmosphere. If, 

 in support of any other theory, a similar mechanical com- 

 bination were proposed to him, he would reject it without 

 hesitation, and say — in order that such phenomena can 

 take place, in order that the lower air should flow horizon- 

 tally towards a particular orifice and then rise vertically 

 through this orifice, it would require to be forced 

 to do so by some sort of indefinite but solid boarding 

 placed over the lower stratum of air and pressing 

 on it with all the weight of the atmosphere. If a 

 hole be made in the boarding, the air will pass through 

 it; but even in this case, its ascensional force deter- 

 mined by the slight difference in density between the 

 layers on each side of the boarding will not be great, 

 and the column of air issuing through the orifice will 

 rise to no great height. In no conceivable case can it 

 ever exhibit the terrible and destructive force of water- 

 spouts and whirlwinds, or indeed any distant approach 

 to it, under even the most favourable conditions. Lastly, 

 let it be granted that the facts really are as they are sup- 

 posed to be, and that the lower stratum of air is on every 

 side in a state of motion towards an orifice of a limited 

 size, where there is no material object to divert it from a 

 horizontal to a vertical course, as in Fig. 7 ; it is plain that 



aerial currents could not change their course so abruptly 

 in order to stream through this imaginary orifice ; they 

 would instantly enlarge and soon altogether efface from 

 the sky the narrow tube of this meteor to which the 



advocate of aspiration clings because it is the sine qua 

 nan of his cherished hypothesis. 



But we shall pass over all these impossibilities which 

 prejudice so readily forgets, and consider the conse- 

 quences which result from this theory— not those which 

 might be drawn to show its utter worthlessness, but those 

 which its own partisans have deduced. It is so easy, 

 from what has been said, to produce a waterspout at will, 

 and everything connected with it — large dense clouds 

 aloft with thunder and torrents of rain — that the idea could 

 not but strike some one. Accordingly, it occurred to 

 several persons in America, where the theory of aspira- 

 tion has been received as favourably as in France, and 

 the artificial production of a waterspout and a thunder- 

 storm in the United States is gravely related in a letter 

 from Mr. G. Mackay, which letter is published in the 

 " Fourth Meteorological Report to the Senate " (Wash- 

 ington, 1857.) It would be a waste of time to make any 

 further reference to an illusion which puts into man's 

 hands the power of originating waterspouts, tornadoes, 

 and typhoons, simply because it makes the phenomena 

 depend on a state of unstable equilibrium in those layers 

 of the atmosphere which immediately surround us. 



Refutation of this Theory. — Let aspiration be established 

 by natural or artificial means at one point in the midst of 

 an absolute calm prevailing in the lower stratum of the 

 atmosphere : there is no reason in such a case why the 



Fig. 9, 



centre of aspiration should be displaced, because all is 

 symmetrical and tranquil round this point. Hence it 

 follows : — (i) Waterspouts, tornadoes, typhoons, and 

 cyclones should be stationary. At most the column of 



