642 



REPORT — 1884, 



; -^ 



ii 



I'll 



111 



-I 

 It 



rather than the ed'ect of the rapid whirUnfT- motion, though in some respoctg 

 indeed, these two conditions can ije rej^arded as hoin<^ mutually causes and effucts 

 each being essential to the maintenance of the other, while there are also some 

 further promoting causes or conditions not as yet here mentioned. 



It st:enis indul)itably to l)e the truth that ordinarily for the genesis of a whiH- 

 ■\vind the two cliicf primarily promiitinir conditions are: — Firstly: A region of 

 diminislied Ijariiiiiciric ])ressui'e ; — this diminution of pressure Ijcing, it may bu 

 presumed, due to rarefaction of Ihe atmosphere over that region by heat and sorae- 

 times further l)y it.s condition as to iniduded watery vapour ; and, s(!condly : A pre- 

 viously existing revolutional motion, or ditl'erential horizontal motion, of the 

 surrounding air ; such revolutional or ditl'erential motion being not necessarily of 

 high velocity at any part. 



Tiie supposed accumulation of air rarefied by heat or otherwise, for producing 

 the abatement of pressure, may, the autlior supposes, in some cases extend upwards 

 throughout the whoh> depth of the atniospluu'e ; and in some cases may be in the form 

 of a lower warm lamina which sonieliow may have been overflowed or covered by 

 colder air above, througli wliicli, or into wliich, it will tendt(t asceml ; or the lower 

 lamina may in sonui casrs b(i warmed in any of sevcjral ways, and so may get a 

 tendency to rise up through tlie colder sr.jierincumbent atmosphere. On this part 

 of the subject, the author believes, there is much scope fjr further researches and 

 advancements both ol)S(n'vatif)nal andconslderational — that is to say, by encouragr- 

 nient of a spirit towards accurate oljservation, and by collection and scrutiny of 

 observiMl facts and appearances, and by careful thc-orctical consideration, founded 

 ou observational results or su}i]iositions. 



To the author it seems probable that the great CAxlones may have their region 

 of rarefied air (extending up ipiite 1o tlie top of the atmosphnn;; wliile often whirl- 

 winds of smaller kinds, many nf the little dust whirlwinds for instance, wliicli are 

 fref|ueutly to be seen, may terminate or gnidually die f)ut at top in a layer or bed 

 of the atmosphere diU'ereiit in it^ conditions, botli as to temperature, and as to 

 original motion from the lower layer in which the whirlwind has been generated. 

 In many sucli cases the upper air may probably be cooler tlian the lower air in 

 which the wliirlwind originates. On the subject of the actions going on at llie 

 upper parts, or upper ends, of whirlwind cores, in most cases, the author feels that 

 he is able to oti'er at present little more than suggestions and speculative conjec- 

 tures. Tn very nnmj' descriptions of the appearances presented by those whirl- 

 winds with visibl • revolving cores, which are called wiiterspouts, it is told that the 

 first appearand! of the so-called waterspout consists in the rapiil shooting down 

 from a dense cloud, of a blade, cloudy streak, seemingly tortuously nnolving, and 

 swaying more or less sidmvise. This is said ra]iidly to prolong itself downwards 

 till it meets the surface of the sea ; and the water of the sea is often imagined and 

 described as rising up bodily, or as ))eing drawn up, into the partial vacuum, or 

 central cohnnnar place of diniinislied ju'essure. The frequently entertained notion 

 — a notion whicli has e\en made its way into writings by men of scienct\ and of 

 authority in meteorology — tlnit Ihe water of the sea is sucked up as a continuous 

 liquid column in tlie centre of waterspout whirlwinds, is by some writers and 

 thinkers rei)udiated as being only a popular fallacy : and it is affirmed tluit it is 

 only the spray from the brolfen waves that is carried up. In this denial of tlie 

 supposition of the water being sucked up as a continuous liquid column, the 

 ftuthor entirely agrees : and he agrees in tlie opiniim that spray or spindrift from 

 the sea, set into viohMit commotion by the whirlwind, is carried up in a central 

 ascending columnar core of air. 



On tlie other hand, the commonly alleged inception of the visible waterspout 

 phenomena, in a descending, tortuously revolving, and laterally bending or swaying, 

 cloudy spindle protruding from a cloud, the author supjioses to be so well 

 accredited by numerous testimonies that it must be seriously taken into account in 

 the development of any true theory and explanation of the physical conditions and 

 actions involved. He ventures to hazard a suggestion at ])resent — perhaps a very 

 crude and rash on(\ It is that the rising central core may perhaps, in virtue of 

 its whiiling motion and centrifugal tendency, afford admission for the cloudy 



