6 14 



NATURE 



[October 23, 1890 



. " the coolness of the wind and that of the atmosphere 

 after the storm is over is hardly to be accounted for 

 otherwise than by supposing that rain is always formed in 

 the cloud overhead, but is re-evaporated before it reaches 

 the earth." 



There is nothing inconsistent in the existence of 

 an excessive pressure at the ground surface beneath a 

 thunder-storm and a diminished pressure in the vortex 

 of the storm-cloud, but in ordinary thunder and hail 

 storms this latter is restricted to the cloud-region. As the 

 barograph traces of these storms show, the oscillations 

 of pressure beneath them are very great, and there may 

 and indeed must be still greater differences between the 

 tornado vortex and the neighbouring region of precipita- 

 tion. Indeed, the great velocity of the air-movement 

 implies as much. 



A part of Ferrel's theory which especially stands in need 

 of confirmation is the assumption that, immediately prior 

 to the formation of the vortex, the vertical distribution of 

 temperature is such as to bring the atmosphere into a 

 state of unstable equilibrium, and that a slight casual local 

 disturbance of this equilibrium starts the vortical uprush. 

 This is also his explanation of cyclone generation, and 

 indeed it is that hitherto held by the majority of writers 

 on the subject. On the other hand, it is generally con- 

 sidered that anticyclones are determined by the greater 

 local density of the atmosphere, due to a low mean tem- 

 perature of the air-column. The last of these assump- 

 tions, even in the case of winter anticyclones accom- 

 panied by very low temperatures at the ground surface, 

 has now been conclusively disproved by Prof. Hann, of 

 Vienna ; and he has also shown very strong reasons for 

 believing that the temperature conditions of extra-tropical 

 cyclones are also incompatible with the prevailing view. 

 It does not, of course, follow that those of tornadoes and 

 hail-storms are equally so, but at least the assumed con- 

 ditions require verification. This may, perhaps, be some 

 day effected by our mountain observatories. 



H. F. B. 



OUR BOOK SHELF. 



Inorganic Chemistry : the Chemistry oj the Non-Metals. 

 By J. Oakley Beuttler, M. A. (London : Relfe Brothers.) 

 Now that there can be obtained a considerable variety of 

 really good text-books of elementary chemistry suitable' for 

 all the usual needs of the present day, one is entitled to 

 look for special features in any new manual. We fail to 

 find any reason for the existence of the volume before us : 

 wherein it differs from others that enjoy general recogni- 

 tion, it is incomplete and erroneous. It has neither index 

 nor contents table, but this is quite a trivial matter when 

 compared with the imperfections of the body of the work. 

 On pp. 19 and 20 there are nine attempts at equations, 

 none of which are correct, while many represent impossible 

 or at least unknown reactions ; and in the following para- 

 graphs, on graphic notation, bonds, and radicles, there is 

 a collection of statements that read like the imperfect 

 recollections of a student who never understood the 

 subject. A single atom of oxygen is shown with curiously 

 shaped projections as an example of an element with an 

 even number of bonds existing as a single "atom- 

 molecule." It is stated emphatically that " the element 

 having the greatest number of bonds is always printed in 

 thick type," but we search in vain for thick type in any 

 formula in the book. The statements that are intended 



NO. 1095, VOL. 42] 



to convey the facts of chemistry are vague, often mislead- 

 ing, and very rarely of a practical character. For an 

 illustration of the style there is no need to go further than 

 the chapter that treats of the first element, hydrogen. It 

 states that " on throwing a piece of sodium into water the 

 sodium combines with part of the hydrogen of the water 

 to form caustic soda, liberating the other part of the 

 hydrogen." The volume closes, as one would expect, with 

 the questions set by various examining bodies during 

 the last three or four years. 



Anatomy, Descriptive and Surgical. By Henry Gray, 

 F.R.S. Twelfth Edition. Edited by T. Pickering 

 Pick. (London : Longmans, Green, and Co., 1890). 

 Of a solid text-book so well known as the present work 

 it is hardly necessary to say more than that a new edition 

 has appeared. The book has been carefully revised, and 

 the editor has added considerably to its value by intro- 

 ducing sections on topographical anatomy, and amplify- 

 ing those on surgical anatomy. Both of these classes of 

 sections have been printed in smaller type, so that they 

 may be disregarded by students who wish to confine their 

 attention exclusively to the descriptive part of the subject. 

 There are many new illustrations, some of which are 

 original. 



The Story of the Heavens. By Sir Robert Stawell Ball, 

 LL.D. Fifteenth Thousand. (London: Cassell and 

 Co., 1890.) 

 It is, for many reasons, satisfactory that there should be 

 a popular demand for a clear, brightly-written work on 

 astronomy. Sir Robert Ball, however, ought hardly to 

 be content with the issue of mere reprints of his book. 

 It may be somewhat misleading to send forth in its ori- 

 ginal form, in 1890, an astronomical work first published 

 in 1886. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature, 

 No notice is taken of anonymous communications. "[ 



The Passage of Electricity through Gases. 



In my letter in Nature of July 24 (p. 295) I objected to 

 Prof. Schuster's statement that the fact that free atoms must 

 turn a gas into a conductor of electricity was fatal to the theory 

 of the electric discharge given by me in the Philosophical Alaga- 

 zine in 1883, and I maintained that the presence of free atoms 

 in a gas free from electric strain was^in no way essential to the 

 theory given in that paper. I see no reason, after reading Prof. 

 Schuster's letter in this week's Nature, to change that opinion. 

 Prof. Schuster bases his statement, not on my description of the 

 theory itself, but on the explanation by it of the weakening of 

 the electric strength produced by a diminution in the density of 

 the gas. A reference to this explanation will show, however, 

 that it really rests solely on the well-known fact that dissociation 

 is assisted by diminution of pressure, and that the passage which 

 Prof. Schuster quotes is merely an explanation of this property 

 of dissociation from the po'nt of view of the kinetic theory of 

 gases ; if this explanation is held to be inconsistent with the 

 absence of free atoms from gas in a normal state, then any 

 alteration in the explanation which might be made to meet this 

 difficulty, though of primary importance in the kinetic theory of 

 gases, is only of secondary importance for the theory of the 

 electric discharge given in my paper, which I still maintain is 

 not all bound up with the existence or non-existence of free 

 atoms in gases not in the electric field. J. J. Thomson. 



Cambridge, October 18. 



Changing the Apparent Direction of Rotation. 



In Nature of October 16 (p. 585), a curious optical effect is 

 incidentally mentioned. Standing near a windmill, and nearly 



