May 26, 1898] 



NATURE 



77 



throughout thoroughly impartial and judicial, and shows 

 a healthy scepticism as regards theories unsupported by 

 adequate fact. There can be no doubt that a trans- 

 lation into English of this admirable book would be of 

 great assistance to all those students of bacteriology who 

 are unable to read it in the original. 



Lehrbuch der Entwicklungsf^eschichte des Menschen. 

 Von Dr. J. KoUmann, o.d. Professor der Anatomie in 

 Basel. Pp. xii +658. (Jena: Gustav Fischer, 1898.) 

 This work appears to approach in method the ideal of 

 an elementary text-book of science, since it gives a sound 

 and well-balanced rhum^ of its subject to date, with 

 references to authorities sufficient to place the student 

 in direct touch with original description of detail. The, 

 pages of the book never pall, and in treatment and mode 

 of expression it is one of the least " German " of German 

 text-books with which we are familiar. It is illustrated 

 by 386 excellent processed drawings, many of which are 

 coloured, and where original these are very good and 

 such as are likely to become popular. The investigations 

 of His, of course, come in for a full share of recognition, 

 and good use has been made of those of Keibel, Mall, 

 Rose, Toldt, and others among recent workers. The 

 book is divided into five leading sections. An intro- 

 duction of sixteen pages is followed by portions dealing 

 with the earlier stages of development ("Progenie" and 

 " Blastogenie "), treated as far as is necessary compara- 

 tively. The fcetal membranes and progressive develop- 

 ment of the human foetus next come in for consideration; 

 but the bulk of the work (405 pages) is of necessity de- 

 voted to a description of the development of systems 

 and organs, and there is appended a twenty-page dis- 

 sertation on heredity. Not the least pleasing feature of 

 the book is its consummately artistic plan. Illustrations 

 never obtrude themselves upon the margin nor over- 

 power the text. In the placing of the figures, choice of 

 their colour and descriptive letterpress, there are evi- 

 dences of the bestowal of great care and forethought and 

 of painstaking consideration of detail, which are alone 

 a strong recommendation of the work. It is carefully 

 written and non-pedantic, and should be deservedly 

 popular. 



Missouri Botanical Garden. Ninth Annual Report. 

 Pp. 160. (St. Louis, Missouri : published by the Board 

 of Trustees, 1898.) 



Administrative details occupy but a small part of this 

 report, the chief contents being a collection of scientific 

 papers and notes on interesting plants, illustrated by 

 several half-tone plates. The results of the studies of 

 the American LemnacecT occurring north of Mexico, by 

 various botanists, are brought together by Mr. C. H. 

 Thompson, and are combined with his own researches 

 into a revision of the order. Mr. H. C. Irish contributes 

 to the report a revision of the genus Capsicum, with 

 especial reference to garden varieties. Mr. J. N, Rose 

 describes five species of agaves which flowered in the 

 Washington Botanic Garden in 1897, and were identified 

 by him. One of these {A. Washin^tonensis) appears to 

 have been hitherto undescribed. Among the notes, Mr. 

 William Trelease, the Director of the Gardens, records 

 some interesting observations on Yuccas. He points out 

 that Yucca gigantea is distinct from Y. gloriosa and Y. 

 (ruatemalensis — its nearest allies — and gives a figure of 

 an Azorean specimen which is a good example of the 

 species. With reference to the extent of the pollination 

 of Yuccas by the Yucca moth, Mr. Trelease has now 

 obtained information which proves the moth to be "the 

 active agent in the pollination of Yuccas from Florida 

 northward as far as fruit is set as a result of Pronuba 

 activity, westward as far as southern California, and into 

 the mountains of northern Mexico to the south." 



NO. 1 49 1, VOL. 58] 



LETTERS ^ TO THE EDITOR 

 [TAe 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 ^NATURE. 

 No notice is taken of anonymous coinmunications.'\ 



Liquefaction of Hydrogen. 



Your last issue contains a report of Prof. Dewar's remarkable 

 achievement in the liquefaction of hydrogen and helium. In his- 

 account of it, which you quote, Prof. Dewar describes the 

 apparatus employed as an enlarged plant of the same type as 

 that used in his hydrogen-jet experiments discussed in his paper 

 before the Chemical Society of December 19, 1895 (see Proceed- 

 ings, No. 158), and in his lecture at the Royal Institution (see 

 Proceedings, 1896), and illustrated in a figure printed with this 

 lecture. An examination of that illustrative figure and of the 

 description shows that the type of apparatus used involves an 

 entirely new departure as compared with the methods of all who 

 had liquefied air before 1895, including Prof. Dewar himself. 

 The new self-intensive method then and now employed is a 

 combination of the following four points : a long tube conveying 

 compressed gas, expansion of the compressed gas through a nozzle- 

 or throttle-valve, direct return of all the expanded gas over 

 the tube of compressed gas, good interchange of temperatures 

 between the compressed and expanded gas. The new method 

 embodying the above combination will be found fully described 

 and illustrated in my patent, No. 10,165, 1895 (May 23). What 

 is equally important historically : in November 1894, more thar* 

 twelve months before Prof. Dewar first showed this new method 

 in action, liquefying air, I had called, with an introduction, on 

 his chief assistant, Mr. R. N. Lennox, at the Royal Institution, 

 had there explained to him this self-intensive method, and had 

 proposed it as a means of obtaining intensely low temperatures. 

 By employing this method I was afterwards the first in this 

 country to liquefy air and oxygen without employing other 

 refrigerants. Since then, at the Royal Institution, where alone- 

 sufficient means are available for the prosecution of these re- 

 searches, the same method has bridged over the space, impas- 

 sable by former methods, between the temperature of liquid air 

 and that of liquid hydrogen and helium, thus proving itself a 

 new and valuable scientific instrument. 



Under these circumstances I think that Prof. Dewar, seeing, 

 he was aware of the facts at the time of his account, ought not 

 to have been content with eulogising the services of his assistant 

 Mr. Lennox, but should also have given me credit for the inven- 

 tion of the method which has procured him so great a success. 

 Although he has been easily able to find in old patents the 

 separate elements which go to make up the new method — this- 

 can be done for any new invention — he has nowhere found, 

 before the date of my communication to Mr. Lennox, that com- 

 bination of the four points given above which is absolutely 

 necessary to his apparatus for liquefying hydrogen. 



The facts referred to above are stated and discussed in greater 

 detail in a paper, to be printed shortly, which was read by me 

 before the Society of Chemical Industry at Burlington House on. 

 the 2nd inst., with illustrative diagrams, and in letters by me to- 

 Engineering {or April 15 and May 6. W. Hami'SON. 



Concerning the Thermodynamic Correction for an 

 Air-Thermometer. 



It is common in works on thermodynamics to give a formula 

 for the thermodynamic correction applicable to an air-thermo- 

 meter ; thp following is substantially the usual proof. 



Accepdng the current theory of the Joule-Thomson experi- 

 ments, we may show that 



,dv M 



t^ - V = k—, 

 dt hp 



where k is the specific heat at constant pressure measured 

 dynamically. From this we obtain 



dt Ip 



and 



ip) ' dt' 



PI <it 

 Thus / is seen to consist of two terms ; the second term. 



