NA TURE 



361 



THURSDAY, FEBRUARY 20, 1890. 



THE PHYSICS AND CHEMISTRY OF THE 

 ''CHALLENGER" EXPEDITION. 



Report 071 the Scientific Results of the Exploring Voyage 

 of H. M.S. "■Challenger^' 1873-76. Physics and Che- 

 mistry, Vol. II. (Published by Order of Her Majesty's 

 Government, 1889.) 



THE second volume of the Report on the Physics and 

 Chemistry of the Challenger Expedition has been 

 published, and contains matter of very great interest. 



The first paper is on the compressibility of water, by 

 Prof. Tait. He has used Amagat's " manometre "k pistons 

 libres." 



" The principle on which the instrument works is 

 the same as that of the Manometre Desgoffes — a sort 

 of inverse of that of the well-known Bramah Press. In 

 the British instrument, pistons of very different sectional 

 area are subjected to the same pressure (thatof one mass 

 of liquid), and the total thrust on each is, of course, pro- 

 portional to its section. In the French instrument, the 

 pistons are subjected to equal total thrusts, being exposed 

 respectively to fluid pressures which are inversely pro- 

 portional to their sections. The British instrument is 

 employed for the purpose of overcoming great resistances 

 by means of moderate forces ; the French, for that of 

 measuring great pressures in terms of small and easily 

 measurable pressures." 



By means of the instrument from his description of 

 which the above is an extract (p. 21), Prof. Tait has de- 

 termined the compressibilities of cistern water, sea water, 

 and solutions of common salt up to pressures of 450 

 atmospheres, and for a range of temperature extending 

 from o^ to 1 5^ C. The results may be briefly summed up 

 as follows. 



The average compressibility of fresh water at o' C. and 

 at low pressures is 520 X lo"'^ per atmosphere. The 

 compressibility is a minimum at 60° C. Both the com- 

 pressibility and the temperature at which the minimum 

 occurs are lowered by pressure. The average compressi- 

 bility for a pressure of 456*9 atmospheres is 478 X 10"'^ 

 per atmosphere, and the temperature of minimum com- 

 pressibility is about 30° C. The average compressibility 

 of sea water is about 0*92 of that of fresh water. The 

 point of minimum compressibility is about 56° C. at 

 atmospheric pressure. 



At o^ C. the average compressibility of water per atmo- 

 sphere may be expressed by the formula o"ooi86/(36 -\- p), 

 where/ is the pressure in tons per square inch. The 

 compressibility of solutions of NaCl, containing s parts 

 of salt to 100 of water, is given by the formula 



o"ooi86/(36 ■{• P ■\- s). 



The depth of a sea about six miles deep is reduced by 

 620 feet by compression. If the ocean were incom- 

 pressible, the level of the surface would be 116 feet 

 higher than it is at present, and about two million square 

 miles of land would be submerged. Finally, the maxi- 

 mum density-point of water is lowered by about 3' C. by 

 an additional pressure of 150 atmospheres, and the tem- 

 perature of maximum density coincides with the freezing- 

 point at - 2°-4 C. under a pressure of 2-14 tons per 

 square inch. 



Vol. xli.— No. 1060. 



It will be seen from this brief recapitulation of his 

 results that Prof. Tait has carried through a very diffi- 

 cult research with success, and has made substantial 

 additions to our knowledge. It may therefore appear 

 ungracious to criticize points which do not touch the 

 essence of the investigation, but it is impossible to read 

 the Report without feeling that, in some respects, it falls 

 short of the standard of classical perfection which ought 

 to be attained in papers published at the national expense 

 to illustrate a great national research. 



In the first place, the C.G.S. system is entirely 

 ignored. As the compressibilities are measured per 

 atmosphere, this is, so far, not of importance ; but in the 

 formulae quoted above, which express the compressibility 

 per atmosphere, terms occur in which the pressures are 

 measured in tons per square inch. The units are thus 

 mixed, and though the requisite data for conversion into 

 atmospheres are supplied, there is no doubt that foreigners 

 will have some difficulty in interpreting the results. 



Again, though we cannot but admire the scrupulous 

 honesty with which he tells the tale, some annoyance 

 may justly be felt that a paper should go forth to the 

 world in a publication intended to mark the highest level 

 to which British science has attained, marred by the 

 confession that the author — who deservedly holds a place 

 in the very foremost ranks of British physicists — had 

 never heard of Van der Waals' work on the continuity 

 j of the liquid and gaseous states till the end of the year 

 1888. 



Van der Waals' investigation was published in Dutch 

 in 1873. In spite of the disadvantage due to the lan- 

 guage in which it was written, its importance was at once 

 recognized. Clerk- Maxwell gave a long account of it in 

 Nature in 1874 (vol. x. p. 477). He returned to the sub- 

 ject in a lecture delivered before the Chemical Society on 

 February 18, 1875, and reported in full in Nature (vol. 

 xi. p. 357). After indicating what he considered to be 

 the weak points of Van der Waals' theory, he added that 

 nevertheless " his attack on this difficult question is so 

 able and so brave, that it cannot fail to give a notable 

 impulse to molecular science. It has certainly directed 

 the attention of more than one inquirer to the study 

 of the Low-Dutch language in which it is written." 

 Maxwell again referred to Van der Waals in his 

 articles on "Atom" and "Capillary Action," published 

 in the " Encyclopaedia Britannica" in 1875 and 1876. So 

 important was the theory considered, that, although it 

 was then four years old, twelve pages were devoted to it 

 in the first number of the " Beiblatter " to Poggcndorff's 

 A}inalen{i^77). O.E. Meyer discussed it inhis"Kinetische 

 Theorie der Case" in the same year. It is described in 

 modern German text-books, such as Riihlmann's " Hand- 

 buch der Mechanischen Warmetheorie," and Winkel- 

 mann's edition of Graham-Otto's " Lehrbuch der Chemie," 

 both published in 1885. It was translated in full into 

 German by Dr. Roth in 1881, and an English translation 

 by Prof. Threlfall, of the University of Sydney, is about 

 to be published by the Physical Society of London. 



In spite of all this, the author of the Report we are dis- 

 cussing informs us, in an addendum da'.ed August 8, 1888, 

 that only a few days before he had been told by a visitor 

 to his laboratory " that one of Van der Waals' papers (he 

 did not know which, but thought it was a recent one) 



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