-JtSNE I, ''1 965] 



wm^tM^ 



<Wi 



the ground in a rude circle, while at the'cen'trfe'aii'ei 

 large blocks which probably formed the central dol- 

 Tnen. " There are two entrances to the enclosure, a 

 northern and a southern, and on the east side of the 

 latter is a large detached mound. Four hundred yards 

 west of the main enclosure is a still larger mound, 

 linown as Gib Hill, connected with it by a low 

 rampart of earth, now nearly worn away." Buxton 

 and Matlock lead Mr. Firth to make some quotations 

 from Erasmus Darwin's poetical references to them in 

 his " Botanic Garden : Economy of Vegetation," and 

 " Loves of the Plants." Dr. Darwin knew and loved 

 the scenes he described, whatever opinion may be 

 held as to his possession of the divine afflatus. There 

 are a few other references to people and scenes of 

 especial interest to the scientific world, but the book 

 will hot be valued for these so much as for its bright 

 narrative of literary and historical centres of Derby- 

 shire, and its fine illustrations. 



The Tower of Pelie. New Studies of the Great 

 Volcano of Martinique. By Prof, .\ngelo Heilprin. 

 Pp. 62 + xxii plates. (Philadelphia and London: 

 Lippincott, 1904.) 

 Prof. Heilprin's latest volume on Martinique is 

 chiefly remarkable for the beautiful photographic 

 plates with which it is illustrated; they give an 

 excellent idea of the features of the great tower of 

 solid lava which for nearly three years has been the 

 centre of interest in the crater of Pel^e. One of 

 these plates, however (No. xi), seems to have been 

 accidentally printed upside down. In the accompany- 

 ing text there is an account of the author's fourth 

 visit to the volcano in June, 1903, and a good deal 

 of somewhat discursive matter regarding the lessons 

 to be learnt from the recent eruptions. The number 

 of points which are still unsettled concerning the 

 mechanism of the explosions and the concomitant 

 phenomena is very large, and the author shows a wise 

 caution in dealing with some of them. He advances 

 the opinion that the tower of Pel6e is a volcanic core 

 of ancient consolidation, and not an extrusion of 

 solidified new lava, as the French observers believe. 

 We cannot believe this is at all likely to obtain general 

 acceptance. J. S. F. 



Experimental Researches on the Flow of Steam 

 Through Nozzles and Orifices. By JK. Rateau. 

 Translated by H. Boyd Brydon. Pp.'iv + 76. (Lon- 

 don : Constable and Co., Ltd., 1905.) Price 4.?. 6d. 

 net. 

 The laws of flow of steam are of much importance in 

 the design of turbines. A clear sketch is given of the 

 theory, and then an account of an excellent experi- 

 mental research to determine the values of the con- 

 stants. .Amongst previous experiments, those of 

 Napier are English, not .American as the author states. 

 The novelty in M. Rateau 's method is the use of an 

 ejector condenser for condensing the steam. The rise 

 of temperature, which is easily measured, gives the 

 quantity of steam condensed. The errors of the 

 method, especially that due to entrained water, are 

 carefully examined. Convergent nozzles and a thin 

 plate orifice were used. The results are compared with 

 those by Hirn on air, and close agreement is found. 

 In a note, the complex phenomenon of the discharge 

 of hot water just on the point of evaporating is 

 examined. 



The translation is clear. It is, however, a defect, for 

 English readers, that the principal formute are left as 

 given by the author in foreign units. The book is 

 essentially one for practical use, and it would have 

 added much to the convenience of engineers if other 

 formulcE than the one on p. 6 had been given in English 

 units. 



NO. 1857, VOL. 72] 



Introductory Mathematics. 'Bf'ti]'' B'/ Motgaftl 

 PfK vi+151. (London: Blackieand Soii.-'Ltd., 1905.) 

 Price 2s. ■■■■," 



In Mr. Morgan's " Introductory Mathematics " the 

 view of the author is that as soon as a boy knows 

 decimal and Vulgar fractions he should begin a mixed 

 course of elementary practical mathematics compris- 

 ing algebra, geometry, and squared-paper work, 

 developed as a whole in mutual dependence, leading, up 

 through the manipulation of formulae to the solution 

 of problems involving simultaneous simple equations 

 and giving a knowledge of the fundamental facts of 

 geometry with a training in practical applications such 

 as the plotting of graphs and of figures to scale, and 

 the fincling of simple areas and volumes. This scheme, 

 ignoring the old water-tight compartment system, is 

 a good one. The chapters on algebra and geometry 

 usually alternate, and the work progresses on natural 

 and easy lines, with illustrations of every-day interest. 

 The author might with advantage have carried the idea 

 still further and have brought in computations from 

 quantitative e.xperimental work in the laboratory, in- 

 volving the use of the balance and measuring flask, and 

 perhaps an inyestigation of the action of forces at a 

 point. There are some minor defects, such as an 

 occasional lack of precision in a statement, bad per- 

 spective in several of the figures, the use of a graph 

 to give a forecast of population fifty years hence, &c. 

 But the treatment of the subject as a whole is very 

 satisfactory ; there is a good collection of exercises, and 

 the book is well suited to its purpose. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to rettirn, 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 Dynamical Theory of Gases and of Radiation. 

 Lord Ravleigh, in a letter which appears in Nature 

 of May iS, opens up the general question of the applic- 

 ability of the theorem of equipartition to the energy of 

 the ether. As the discussion has arisen out of my 

 " Theory of Gases," may I, by way of personal e.xplan- 

 ation, say that although I was fully alive to the questions 

 referred to in this letter when writing my book, yet it 

 seemed to me better not to drag the whole subject of 

 radiation into a book on gases, but to reserve it for sub- 

 sequent discussion? Since then I have written two papers 

 in which questions similar to those raised by Lord Ray- 

 leigh are discussed from different aspects, but as neither 

 of these papers is yet in print, I ask for space for a 

 short reply e.xplaining how my contentions bear on the 

 special points raised by Lord Rayleigh's letter. 



May I, in the first place, suggest that the slowness with 

 which energy is transferred to the quicker modes of ether- 

 vibration is a matter of calculation, and not of specula- 

 tion ? If the average time of collision of two molecules 

 in a gas is a great multiple N of the period of a vibra- 

 tion, whether of matter or of ether, then the average 

 transfer of energy to the vibration per collision can be 

 shown to contain a factor of the order of smallness of 

 c'-N. The calculations will be found in §§ 236-244 of 

 my book. It is on these that I base my position, not on 

 a mere speculation that the rate of transfer may be slow. 

 Lord Rayleigh's example of a stretched string, say a 

 piano wire, will illustrate the physical principle involved. 

 If a piano hammer is heavily felted, the impact is of long 

 duration compared with the shortest periods of vibration, 

 so that the quickest vibrations are left with very little 

 energy after the impact, and the higher harmonics are 

 not heard. If the felting is worn away, the impact is of 

 shorter duration, the higher harmonics are sounded, and 

 the tone of the wire is " metallic." ' 



The factor e-N is so small for most of the ether- 

 vibrations as to be negligible. There is no sharp line of 

 demarcation between those vibrations which acquire energy 



