Oct.. 30, iS 84] 



NA TURli 



649 



so-called waterspout consists in the rapid sho -ting down from a 

 dense cloud of a black cloudy streak, seemingly tortuously re- 

 volving and swaying more or less sidewise. This is said rapidly 

 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 being drawn up, into the partial vacuum 

 or central columnar place of diminished pressure. The frequently 

 entertained notion — a notion which has even made its way into 

 writings by men of science and of authority in meteorology — that 

 the water of the sea is sucked up as a continuous liquid column 

 in the centre of waterspout whirlwinds, is by some writers and 

 thinkers repudiated as being only a popular fallacy, and it is 

 affirmed that it is only the spray from the broken waves that is 

 carried up. In this denial of the supposition of the water being 

 sucked up as a continuous liquid column the author entirely 

 agrees, and he agrees in the opinion that spray or spindrift from 

 the sea set into violent commotion by the whirlwind is carried 

 up in a central ascending columnar core of air. 



On the 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 supposes 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 present — perhaps a very crude 

 and rash one. It is that the rising central core may perhaps, in 

 virtue of its whirling motion and centrifugal tendency, afford 

 admission for the cloudy stratum to penetrate down as an inner 

 core within that revolving ascending core now itself become 

 tubular. The cloudy stratum may be supposed not originally to 

 have been endowed with the revolutional motion or differential 

 horizontal motion with which the lower stratum of thermally 

 expanded air has been assumed to be originally endowed. The 

 upper stratum of air from which the cloudy spindle core is here 

 taken to protrude down into the tubular funnel is not to be 

 supposed to be cold enough to tend to sink by mere gravity. 

 Though it were warm enough to allow of its floating freely on 

 the thermally expanded air below, it could still be sucked down 

 into the centre of the revolving ascending core of the whirlwind. 

 Not to proceed further on this occasion with attempts towards 

 explanation of the difficult subject of the actions at the upper 

 ends of waterspout whirlwinds, the author wishes to have it 

 understood that his main object in proceeding to prepare the 

 present paper was to put forward clearly the theory he has given 

 as to influx at the bottom in consequence of abatement of whirl 

 in the lamina close to the sea-surface by frictional resistance 

 there. 



Addendum. — A few brief explanations and references will 

 now be added to assist in the understanding of some of the 

 principles assumed in what has been already said. It is to be 

 clearly understood that, in a whirling fluid, even if the velocity 

 of the whirling motion be very small at great distances from the 

 axis, if the fluid be impelled inwards by forces directed towards 

 the axis, the absolute velocity will grea tly increase with diminu- 

 tion of distance from the axis. Thus in the whirlpool of free 

 mobility, in which the particles are perfectly free to move out- 

 ward or inward, the velocities of the particles are inversely 

 proportional to the distances from the axis, the fluid being under- 

 stood to be inviscid or frictionless. On this subject reference 

 may be made to a paper by the author on " Whirling Fluids," 

 published in the British Association volume for the Belfast 

 Meeting, 1852. Again, as to the inward flow caused in a fric 

 tionally retarded bottom lamina of a whirlwind or whirlpool 

 with vertical axis, by the frictional retardation from the bottom 

 on which the whirling fluid rests, reference may be made to a 

 paper by the author, " On the Grand Currents of Atmospheric 

 Circulation" in the British Association Report, Dublin Meeting, 

 1857, part ii. p. 38. On another case of the manifestation of the 

 same principle, reference may be made to a paper by the author 

 in the Proceedings of the Royal Society for May 1 876, in re- 

 spect to the " Flow of Water round Bends in Rivers, Sec," with 

 reference to the effects of frictional resistance from the channel 

 in the bends ; and to another paper by him, on the same subject, 

 in the Proceedings of the Institution of Mechanical Engineers 

 (August 1879, p. 456), where the inward flow is explained as 

 •xperimentally exhibited. 



Postscript of date August 16. — Prof. James Thomson wishes 

 now to offer in continuation of his paper on " Whirlwinds and 

 Waterspouts," despatched two days ago for Montreal the follow- 



ing postscript, which will extend the considerations there already 

 put forward, and will tend to modify or amend some of them ; 

 but will leave unchanged the theory as to influx of the bottom 

 lamina of the whirlwind towards the central region in conse- 

 quence of the frictional resistance offered by the surface of 

 the sea to the air whirling in close contiguity upon that surface. 

 He wishes to put forward the question as to whether it may 

 not be possible, in some cases of whirlwinds, for the barometric 

 pressure in the central or axial region to become abated through 

 the combined influences of rarefaction by heat (increased, perhaps, 

 by conditions as to included moisture) on the one hand, and the 

 whirling motion on the other hand, very much beyond the 

 abatement that could be due to heat, or heat and moisture, alone, 

 without the whirling motion. He thinks it very likely that in 

 great whirlwinds, including those which produce the remarkable 

 phenomena called waterspouts, it may be impossible for the 

 whirling action to be confined to the lower region of the atmo- 

 sphere ; but that, even if commenced there, it would speedily 

 be propagated to the top. It seems also not unlikely, and in 

 some trains of thought it comes to appear very probable, that the 

 whirling fluid, ascending by its levity, would drive outwards 

 from above it all other air endowed with less whirling energy, and 

 would be continually clearing away upwards and outwards the 

 less energetic axial core which enters from below, and any, if 

 such there be, that has entered from above. He is unable at 

 present to offer much in further elucidation (possibly it might 

 only prove to be in further involvement) of this very difficult 

 subject. He thinks the question should at least be kept open as 

 to whether the whirling and scouring action may not go forward 

 growing more and more intense, promoted always by energies 

 from the thermal sources which have produced differences of 

 temperature and moisture in different parts of the atmosphere, 

 and that thus a much nearer approach to vacuum in the centre 

 may be caused than would be due merely to the levity of the 

 superincumbent air if not whirling. 



He also wishes to suggest that the dark and often frightful 

 cloud usually seen in the early stages of whirlwinds and water- 

 spouts, and the dark columnar revolving core often seen appa- 

 rently protruding downwards from the cloud, may be due to 

 precipitation of moisture into the condition of fog or cloud, on 

 account of abatement of pressure by ascension in level, and en- 

 vironment with whirling air, which by its centrifugal tendency 

 acts in protecting the axial region from the pressure inwards of 

 the surrounding atmosphere. 



UNIVERSITY AND EDUCATIONAL 



INTELLIGENCE 



Cambridge. — Dr. Besant and Mr. C. H. Prior are appointed 



Moderators, and Messrs. C Graham and A. J. C. Allen 



Examiners, in the Mathematical Tripos for the year beginning 



May I, 1885. 



The following Natural Science Examiners have been ap- 

 pointed : — Physics : Prof. A. Schuster and Mr. W. N. Shaw ; 

 Chemistry : Messrs. A. Scott and M. Pattison Muir ; Mine- 

 ralogy : Prof. Lewis and Mr. H. P. Gumey ; Geology : Messrs. 

 R. D. Roberts and J. J. H. Teall : Botany : Messrs. F. 

 Darwin and H. M. Ward; Zoology: Prof. A. M. Marshall 

 and Mr. A. Sedgwick ; Human Anatomy : Prof. A. Macalister 

 and Mr. A. Hill ; Physiology : Prof. Michael Foster and Mr. 

 J. N. Langley. 



St. John's College offers for competition in December next a 

 large number of Open Scholarships, Exhibitions, and Sizarships. 

 Natural Science is one of the subjects which, taken singly, may 

 lead to election to any of these. The subjects are in general 

 those of the Natural Sciences Tripos ; but every candidate in 

 Natural Science must show a competent knowledge of two at 

 least of the following subjects : — Physics, Chemistry, and 

 Biology, all in an elementary sense. A candidate, however, 

 may be elected on the ground of special proficiency in any one 

 of the subjects of examination. There will be both papers and 

 practical work in all subjects. Further information may be 

 obtained from the tutors. 



Trinity College Examinations begin on December 11. Major 

 and Minor Scholarships, Exhibitions, and Sizarships may be 

 given for Natural Science. One Exhibition at least, of the value 

 of 50'., will be given for Natural Science to a candidate not yet 

 in residence at the University. 



King's College offers an Exhibition of 60/. per annum for 

 Natural Science: examination on December 11. 



