i88 



NA TURE 



[Februarv 21, 1895 



motion is opposed by an internal resistance or friction 

 which is measured by the logarithmic decrement and is 

 distinct from the elastic after-etTect. In the new edition 

 six pages are devoted to Boltzmanns theory of internal 

 friction of solid bodies, according to which the damping 

 of oscillations is regarded as due to the elastic after- 

 etTect, the result of which is that the force urging the wire 

 towards its position of equilibrium is not proportional to 

 the displacement. In the fourth edition there was little, 

 about " Hardness," beyond a list of the substances form- 

 ing Moh's scale ; indeed, the whole article on the different 

 kinds of /Vj//>/t«/ was rather unsatisfactory. Now the 

 researches of Hertz and the experiments of .Xuerbach 

 have made it possible to measure the hardness of a sub- 

 stance absolutely and without reference to the properties 

 of any other substance. 



Instead of being relegated to the volume on heat, as in 

 some text-books, the kinetic theory of gases is here de- 

 scribed at considerable length in the section treating of 

 the properties of gases. This section has been over- 

 hauled, and Stefan's theory of gaseous diffusion is given 

 in place of O. E. Meyer's. Prof. Wiillner attaches so 

 much importance to recent developments of the electro- 

 magnetic theory of light, that he has determined to alter 

 the sequence of the subjects in his treatise, so that light 

 and radiation may come at the end. In the edition now 

 appcanng, the second volume will therefore treat of heat, 

 and the third of electricity. pi: 



Peru. Beohachtttngen unci Studicn iibcr das Land iind 



seine Bcwolmcr wdltrcnd eincs lyjulirigen Atifcnllialls. 



Von E. W. Middendorf. (Berlin : Robert Oppenheim, 



1893-94.) 

 Dr. Middendorf commences his treatise on Peru by 

 a long preface detailing the circumstances which led him 

 to choose that country for his home. Starting as the 

 surgeon of an Australian emigrant ship from Hamburg 

 in 1854, he narrates the incidents of the voyage, an 

 epidemic of cholera and other irrelevant accidents in- 

 cluded, until on the return journey, sick of the sea, he 

 left his vessel in Valparaiso, and after some further 

 wandering took up his residence in Peru, and was led by 

 degrees to pay closer and closer attention to the land and 

 people of his choice. 



The work is planned in three parts. The first volume 

 deals nominally with Lima, the capital ol the republic, 

 but is really much wider in its scope, commencing with 

 the history of Peru, and after describing the town with 

 its streets and public buildings in somewhat tedious 

 detail, proceeding to discuss the genera linstitutions of 

 the country from the standpoint of the capital. People, 

 church, government, law, education, commerce, transport, 

 and charities arc all discussed ; and at the end two 

 chapters describe the municipal markets, slaughter- 

 houses, water-works, bull-fighting arenas, theatres, and 

 other places of amusement. The second volume de- 

 scribes the coast lands of Peru northward and southward 

 of the capital, the towns and seaports, the provinces 

 now ceded to Chile, the railway communications, and 

 the antiquities. A third volume is promised dealing 

 with the highlands, but presumably the scheme does 

 not include an account of trans-Andine Peru. 



\Vc cannot look on Dr. Middcndorf's work as an 

 exhaustive or even a comprehensive work on Peru. It 

 IS indeed a book lor the general reader rather than the 

 student. Abounding as it does in personal reminiscences, 

 and written in an easy conversational style, it should do 

 much to further the knowledge of the country it describes 

 amongst (jcrman-speaking people. IJut it is, we fear, 

 too diffuse and bulky to serve tins purpose with the same 

 degree of satisfaction that a smaller work might have 

 secured, and it lacks firm and wide generalisations 

 which could present a clear picture of the land and people 

 as a whole. 



NO. I 32 I, VOL. 51] 



LETTERS TO THE EDITOR. 



\Thc Editor does not hold himself responsible for opinions t.\ 

 pressed by his correspondents. Niither can he undertak. 

 to return, or to correspond -.vith the writers of, reieclc. 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications.} 



The Liquefaction of Gases. 



A CAREKUL Study of his letter in Natuki; of February 14 

 shows that Prof. Dew.ir makes four c'.iim'!. 



(i) He claims that in his lecture in 1SS4 he employed an ap 

 paralus "more readily and quickly handled" than that of 

 Messrs. Wroblewski and Olszewski, in the illustrations he gave 

 of the work of these investigators. 



(2) He claims that in tiis lecture in 1S84 he used liquii. 

 nitrous oxide for ihe production of liquid oxygen. 



(3) He claims that in 1SS6 he li'iuefitd oxygen by passir, 

 the gas through a long copper coil surrounded by liquid eihylent 

 and that his apparatus made it possible to transfer the liquii: 

 oxygen to a glass vessel wherein it could be used as a cooling 

 agent. 



(4) He claims that, in conjunction with Prof. Liveing, h;. 

 deterojined the refractive index of lii|uid oxygen before the pub- 

 lication of Prof. Olszewski's first paper on the subject. 



I shall consider these claims in order. 



(1) The apparatus used by Messrs. Wroblewski and Olszewski 

 in 1SS3 is fully described and figured in H'iedemanii' 

 Aiinalcn for that year (xx., 243). The gas to be liquefied wa- 

 strongly compressed in a glass tube, imbedded in an iron 

 cylinder, and connected by a capillary tube with a glass vessel, 

 which in turn was connected with a slore of liquid elhyleoe, 

 previously cooled by passing through a narrow copper lube twr 

 metres long immersed in a bath of solid carbon dioxide ; tlu 

 glass vessel was also connected with a double oscillating I'ianchi 

 air-pump. The liquefied gas was collected in the glass vessel, 

 and its properties were examined. A comparison of the appa 

 ratus of ihe Polish Professors with the brief de.scripiiiin in tlu 

 Proceedings of Ihe Royal Institution of the apparaius used by 

 Prof. Dewar in 1S84 "for the purpose of lecture demonstra- 

 tion" will, I think, show that I slated the mailer fairly in my 

 former leiter by siying that Prof. Dewar "describes and figures 

 an apparaius which is a slightly modified form of that of thfr 

 Polish Professors, which in turn was derived from the 

 apparatus of Caillelel." 



(2) If anything was gained by using liquid nitrous oxide for 

 Ihe liquefaction of oxygen, why has not Piof. Dewar continuei'. 

 to use this refrigerator? 



Prof. Dewar claims to have devised a inetho 1 f 'r liquefying 

 oxygen which was so much inferior to that brought into prac- 

 tice by Wroblewski and Olszewski that it was abandoned almost 

 as soon as it was devised. I suppose his claim may be admittc ' 

 here. 



(3) Granting that the substilulion of a long copper coil for 

 strong glass luhe was an improvement, it must not be forgotlci 

 ihat the apparaius of .Messrs. Wroblewski and Olszewski, de 

 scribed in 18S3, enabled the liquefied gas to be collected in 

 vessel wherein its properties not only might be, but were, 

 studied. That this apparaius was an efricirnt insuumen; i- 

 shown by the facts that before ihe year(iS86) in which thi 

 copper coil method was described, Profs. Wroblewski an. 

 Olszewski had liquefied oxygen, nitrogen, and carbon monoxide 

 Prof. Olszewski had liquefied air, nitric oxide, and marsh gas ; 

 h.ad determined the boiling poinis, at atmospheric picssurc, and 

 the criiical temperatures and pressure?, of these .six gases ; ha>', 

 solidified nitrogen, chlorine, hydrogen chloride, nilric oxide 

 carbon monoxide, and marsh gas ; and h.ad made careful deter 

 minalions of ihe behaviour of hydrogen at - 211 and - Jjo . 

 Hut with his copper coil 45 feet long Prof. Dewar did nothing 

 for, so far as can be judged fiom his published papers, he Av' 

 not initialc experimenis on the properties of liquefied oxygen, 

 nitrogen, or ai', until 1S91 92. I think we may conclude tb.i' 

 Ihe apparaius of Ihe Polish Professors was beiui adapted foi 

 accuralc wink thr'n "that made wholly of mclal " t" 

 which Prof Dewar refers. If Prof Ilewar's apparaius oi 

 1SS6 was "safer and better" ihan " ihat used in Cracow in 

 i8yo"— as he says it was— why was not this safer and heller 

 apparatus lurn<d to some scienlihc use before a descriplior. 

 appeared of ihe apparatus of Prof. Olszewski, in which the 

 gases were liquefied in a steel cylinder and then transferred l> 



