436 



NA TURE 



[March 7, 1895 



Pnp.iratory Physics. By William J. Hopkins. (London : 



Longmdns, Green, and Co., 1894.) 

 The course here presented is the outgrowth of needs of 

 the clas^ei beginning the study of physics in the Urexel 

 Institute, Philadelphia. It is arranged strictly for 

 laboratory work, and although the ground covered is not 

 very e.xtensive, yet sufficient has been selected for a first 

 couise, and that expounded to a very full extent. 

 .Mechanics has been chietly taken in hand, and the 

 numerous problems have been so arranged that the 

 student is able to investigate them experimentally for him- 

 self. A glance at the instructions and explanations shows 

 one that the auihor wishes at every step to instil into the 

 beginner the idea that habits of accurate and thorough ob- 

 servation must be developed, and, further, that students 

 must be careful, comijlete, and orderly in recording and 

 arranging his results. With this intention most of the ex- 

 periments are accompanied with printed forms illustrating 

 concise methods of recording the observations. The 

 apparatus alluded to in the text is of a simple nature, and 

 quite sufficient for those beginning the subject. As an 

 introduction, a few pages are devoted to such fundamental 

 points as units, errors and sources of error, coordinates, 

 plotting of curves, i:c. Altogether, the book will be 

 found a serviceable and able help to all wishing to 

 take part in the more simple laboratory work. 



The Story of the Stars. By George F. Chambers, 

 F.R.A.S. Pp. 192. (London: George Newnes, Limited, 

 1S95.) 

 One or both of two qualifications are essential in a book 

 designed for general readers; the text mu^t be attiac- 

 tively written, or the illustrations must plea e the eye. 

 This book has neither of these claims to public favour: 

 the text IS stodgy and the illustrations are the very worst 

 that we have seen disfiguring a volume on astronomy. 

 The former detect is due to the author's attempt to say 

 something about the whole of sidereal astronomy in le:.s 

 than two hundred small pages; the wretched illustrations 

 cannot be due to his inability to find others, so this fault 

 must lie at the publisher's door. And yet we cannot 

 understand why the publisher of the Strand .Max^aziiie 

 and other pictorial papers could not give the same care 

 to the Illustration of a book on astronomy as he does to 

 the description of the home of some celebrity. Only in 

 regard 10 quantity of information are we aule to say a 

 favour.ible word for this book. Mr. Chambers is 

 thoroughly competent to collect the facts belong. ng to 

 the old astronomy, and to condense them. He may be 

 able to coinpre-.sa mass of knowledge into a s.nall com- 

 pass, but his latest production shows that he his not ihe ! 

 \.OVic\\ simplex muiiditiis of a writer for the popular mind. I 



Aerial i^'avi^ation : Proceeditij^s of the Internalional 

 Conference held at Chicaj(o, Aiif;usl 1893. Pp. 429. 

 (New Yo'k: American Enj^ineer Office. London: 

 Sampson Low, Marston, & Co., 1894.) 

 An International Conference on aerial navigation formed 

 one o( the series of Congresses which were held in 

 Chicago during tne summer o( 1893. The meeiings proved 

 to be suctessfiil, and the volume in which the pro- 

 ceedings are recorded shows that facts and positive 

 knowledge, rather than speculations or descriptions ol 

 things "in the air," were the order of the day. Some 

 thirty-five papers were presented, each containing an 

 account o( observations and results of experiments 

 carried out by scientific men or experienced engineers. 

 These p.ipers and the discus%ions upon them aie now 

 publl^he(l in a volume uniform with Mr. Chanute's 

 treatise on "Fl)ing NLichmes," previously noticed in 

 Naii;re(voI I. p. 569, l«94). Both show that many 

 of the proiilcrns of aeronautics and avi.ition are being 

 treated scien'ifically. The present volume is of special 

 interest to meteorologists, for it contains several papers 

 on the exploration ot the upper atmosphere. 



NO. 1323. VOL. 51] 



LETTERS TO THE EDITOR. 



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

 pressed ty his correspondents. Ntither can he undertaki- 

 to return, or to lorrespon t with the writers of rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications. ] 



The Liquefaction of Gases. 



I DECLINE to fol ow Prof. I)ew;ir into the fre^ih crop of 

 irrelevant side issues r.iiscd by liis leiier in Nature of 

 Fe'iruary 28. Ihe charge bi ought .iijainst Pro(. Dewar, 

 which I think I have amply substantiated, is that he has allowed 

 the lmpre^slon to go abr ad that he has carried out much 

 original re-eirch in'o the methods of liquefyini; the more per- 

 manent gases, and the proper ies of the liquids produced ; 

 whereas his experiments have been mainly rtpetitions of work 

 dune I'y others. 



Pr if. Dewar has not met this accusation. He has not proved 

 that bis methods for liipieiying the more permanent ga>es are 

 original methods, he has not even shown ihat lor scieniific pur- 

 po-es they are g lod meihods ; he lias not proved that his ex- 

 periments on ihe liquefied gases are either original or valuable ; 

 he has no aiicmpiedio r<but the actual lacis, or to deal with the 

 actual dates, brought forward liy Prof. Olszewski and myself. 



In his last letter Prof. Dewar g vcs a list ol work "com- 

 menced and so far devtlo|jcl in the laboratory of ihe Royal 

 Insiitu ion " The list might, however, have been made a little 

 less grotesque by the ou.ission ol such tliin s as 'argon in 

 liquid air," and the " liquefaction of hydrogen," and the substi- 

 tution in place of these 01 a doul le &c. 



When Prof. Dewar quits the region of romance, and tries to 

 meet the dctiniie s atcments I have made, and the evidence 

 alT'rded by the dates I have quuied, I .shall be rtady 10 deal 

 with his aigumcrrs to the best of my ability. 



Cambridge, i\Iar';h 2. M. M. Pattiso.n Muik. 



Eleven-year Sun-spot Weather Period and its 

 Multiples. 



Many years ago, investigations in regard to the existence of a 

 period of about eleven yeara in the weather corresponding with 

 the eleven-year sun-spot period were actively carried out in 

 vari >us pans of the worlii. Much data was accumuhiieil in sup- 

 port ol such a period, a large pan of which was pulilished in 

 the earlier volumes of Naturk. Hut the iiivesiigaiions, as a 

 whole, showed thai the pcnod was less marked or more com- 

 plex than at first aniKipaied, so ihat recently less interest has 

 tjeen maniiesied in the subject, and indeed many express their 

 doubis as 10 the rxisience of such a period. 



One of the complixiues which has helped lo obscure the 

 clevei.-year period is ihe existence of what may perhaps be 

 called weather harmonics, on account of the resemblance lo har- 

 monics in sound — thai IS, the existence of other perioos related 

 to the length of the first as 2, 3, 4, Jic. Thus ihe existence of 

 ihe eleven-year period is obscured by the existence of other 

 periods of 22, a, 44, &c., years. 



If the leailer will turn lo the letter " On Some Tempeiatuve 

 Variations in France and Giecnlanil," in NatURF. ol October 

 II, 1894, he will find ploiied the smoothed number of frost 

 <f.iys ana mean July tcnipeiaiures at Pans for a laige part of 

 the i>ies' nl century. These curves show three marked waves 

 in the temperature with the crests about 1S25, 1848, and 1869, 

 that is, almost exactly 22 years apart. If the dales ol the chief 

 maxima and minima of ifie individual curves are arranged under 

 ditcs 22 years a(iart, as shown below, it will be seen that the 

 dates closely apiiroximate, thus : — 

 Mean dales of 



If only the iwo highest maxima arc consirlered, ilicy occurred 

 about 1826 and 1870, or 44 years apart ; but if all the secondary 



