544 



NATURE 



{Oct. 25, 1877 



the Liverworts and Characes, with an appendix to the 

 species of Mosses and Hepaticae, and a copious index. 

 The vascular cryptogams are described by Stenzel, and 

 include twenty-one genera, fifty-three species, and ten 

 sub-species. A history of the discovery of Silesian 

 Pteridophyta is prefixed, and an interesting account of their 

 distribution. Thus the species found on serpentine, 

 limestone, and other rocks, are noted, as well as the 

 hypsometrical distribution. Four regions of elevation are 

 distinguished: i, from 55 metres to 150m. ; 2, from 150 

 m. to 500 m. ; 3, from 500 m. to 1,100 m. ; and 4, from 

 1,100 m. to 1,500 m. The arrangement of some of the 

 species and sub-species is not quite in accordance with 

 our English ideas. Thus Woodsia hyperborea, Koch, is 

 separated into two sub-species : i, arvonica, With. ; and 

 2, rufiditla, Svv. ; equal to hyperborea R., Br. and ilvemis 

 R., Br. respectively. Cystopteris niontana of British 

 botanists is C. siidetka, Al. Braun and Milde. Then A. 

 dilatatinii, spinulositin, and cristaliiin, are all placed as 

 s\xh-s^ecitsolAspidiii>?ispi!iulosiiii!,Svi.,3J\d.A.aculeafu>n 

 lobatum, and align hire are made sub-species of A. 

 aculcatuiii, Doll. 



The Mosses and Liverworts are described by Limpricht, 

 and occupy the greater part of the volume, there being 

 106 genera and 464 species of Mosses, and 39 genera and 

 132 species of Hcpatica5. A i^^ additional species are 

 added in the Appendix, bringing up the Mosses to 492 

 species and the Liverworts to 155. The same arrange- 

 ment is here followed as to history and distribution as in 

 the case of the vascular cryptogams. The descriptions 

 seem excellent, and the information given very full and 

 complete^ the characters of the orders and families being 

 given in great detail. 



The Characea; have been described by Prof. Alexander 

 Braun. Probably this was one of the last important 

 works from his prolific pen. All must deplore his recent 

 loss. His vast knowledge, the importance of his con- 

 tributions to botany, and his genial kindly manner, the 

 readiness he always showed in assisting his students, are 

 well known. To know him was to love him, and we 

 esteem it a high privilege to have been one of his students. 

 The Characese are not very numerous, three genera and 

 fourteen species being enumerated ; but in the hands of 

 Prof. Braun it becomes a most valuable memoir on the 

 whole group, while the species hkely to be found in 

 Silesia are all pointed out. The synonymy must be very 

 confused, as Braun notices that Chara Jlexilis, Waller, 

 includes three or four species of Nitella, three of Toly- 

 pella, and one C/iara, C. gracilis of Sprengel is a still 

 greater monster, as it includes five species of Nitella, one 

 Lychiiolhamnus, and three species of Chara. 



W. R. MCNAB 

 The Countries of the World, being a Popular Descrip- 

 tion of the Various Continents, Islands, Rivers, Seas, 

 and Peoples of the Globe. By RobertJBrown, M.A., 

 Ph.D., &c. Vol. I. (London : Cassell, Fetter, and 

 Galpin. No date.) 

 This is certainly an attractive book ; the wealth of illus- 

 trations renders it so. While we recognise some of the 

 illustrations as having done service elsewhere, many of 

 tehm are new, well-executed, and afford a good idea of 

 the scenery, products, and people of the regions they are 

 meant to illustrate. This volume treats of the Arctic 

 regions and North America, contains a great amount of 

 miscellaneous information, and is written in a rambling 

 easy-going style. It is essentially a popular work, but 

 might have been made valuable even to the geographical 

 student had some of the pictures been dispensed with 

 and a number of regional maps substituted similar to 

 those which are so important a feature in Reclus' 

 " Geographie Universelle," with which masterly and ex- 

 haustive work, however, it would be unfair to compare it. 

 We have no doubt Dr. Brown's work will afford pleasure 

 and prove instructive to many readers. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsiMe for opinions expressed 

 by his correspondents. Neither can he undalake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible othenuise to ensure the appearance even of com- 

 munications containing interesting and novel factsi\ 



The Radiometer and its Lessons 

 Having been prevented from attending the recent meeting of 

 the British Association by the necessity of devoting my entire 

 vacation to mental and bodily renovation after the sad family 

 losses I had sustained, I have only become aware within the last 

 few days that my article in the April number of the Nineteenth Cen- 

 tury, entitled "The Radiometer and its Lessons," had been 

 there spoken of by Prof. 0. Cavey Foster, in his address as Presi- 

 dent of Section A, as showing an "unmistakable tendency, 

 either inliiituvially or unintcntionaUy, to depreciate Mr. Crookes's 

 merits, and to make it appear that he had put a wrong interpre- 

 tation upon his own results," which st.atement is said by your 

 reporter to have " elicited great applause." 



Of Mr. Crookes's own reply in the July number of the same 

 periodical, entitled " More Lessons from the Radiometer," I 

 took no notice ; partly because my mind was at the time fully 

 occupied by sad cares and urgent duties, and partly because 

 I thought that his assertions (i) that he had not theorised on the 

 subject at all, (2) that he had not attributed the rotation of the 

 radiometer to the direct impetus of light, and (3) that he had 

 never claimed the discovery of a new force or a new mode of 

 force, were so well known in the scientific world to be incon- 

 sistent with fact, that I need not trouble myself to refute them. 

 Prof. Carey Foster, however, speaking with authority as Pre- 

 sident of the Physical section of the British Association, has 

 given it as his judicial opinion that what I have written on this 

 subject shows an unmistakable tendency to depreciate Mr. 

 Crookes's merits, and to misrepresent his opinions ; and he has 

 further "unmistakably" suggested (as it appears to me) that 

 this may have been done with deliberate intention, instead of 

 being done in good faith under the influence of an unintentional 

 bias. As it is impossible for me to allow such an imputation 

 from such a quarter to pass unnoticed, I might fairly challenge 

 Prof. Carey Foster to justify language which I must presume him 

 to have used with all due consideration of its obvious meaning, 

 and of his and Jiiy relative positions. But as he explicitly dis- 

 avows the more serious part of this imputation, I have now only 

 to ask to be allowed to show. In the columns of the journal 

 which has not only recorded the accusation, but has pointedly 

 directed attention to it, — first, that I have not, even unintention- 

 ally, ' ' depreciated Mr. Crookes's merits " as the inventor of the 

 Radiometer ; and secondly, that Mr. Crookes really did in the 

 first instance put that "wrong interpretation upon his own 

 results " which I attributed to him. Had Prof. Carey Foster 

 complied with the request I privately made him, that he should 

 specify the passages which (in his opinion) justify his charge, I 

 should have been able to reply to it much more briefly. But by 

 declining thus to particularise, he obliges me to traverse the 

 whole ground covered by his general accusation. 



That I was not influenced, v/heu writing on the Radiometer, 

 by any animus arising from my personal antagonism to Mr. 

 Crookes on another subject, will appear, I think, from the 

 following extracts from the two lectures which I delivered at the 

 London Institution (by special request) on Mesmerism, Spiri- 

 tualism, &c., before Christmas, and which were published in 

 Eraser's Alngazine at the commencement of the present year : — 



"The recent historyof Mr. Crookes's most admirable invention, 

 the Radiometer, is pregnant with lessons on this point. When 

 this was first exhibited to the admiring gaze of the large body 

 of scientific men assembled at the soiriie of the Royal Society, 

 there was probably no one who was not ready to believe with its 

 inventor that the driving-round of its vanes was effected by the 

 direct mechanical aid of that mode of Radiant Force which we call 

 Light ; and the eminent Physicists in whose judgment the greatest 

 confidence was placed, seemed to have no doubt that this mecha- 

 nical agency was something outside Optics properly so called, 

 and was, in fact, if not a new Force in nature, a new modus 

 operandi of a force previously known under another form. 

 There was here, then, a perfect readiness to admit a novelty 



