August 27, 1908J 



NA TURE 



401 



A number of instances are given of the value of mathe- 

 matical research, and a plea is made for greater encourage- 

 ment for mathematicians and more serious work in higher 

 education. For example, as Prof. Bryan points out, 

 " Before the mathematical theory of stability had been 

 developed many ships were sunk and many lives lost which 

 could have been saved if the problem had been properly 

 placed in the hands of the mathematician. It was only 

 after these losses took place that the theory of the meta- 

 centre was finally evolved, and the problem of stability 

 was reduced to one of pure arithmetical calculation. If 

 one-tenth of the money expended in building these ill-fated 

 ships had been offered to a really competent mathematician 

 possessing the highest knowledge of his subject, to enable 

 him to devote his whole time for a year or so to this 

 particular problem, the saving to the community would 

 have been immense. Yet a similar drama may be enacted 

 at the present day in connection with artificial flight, for 

 while the mathematical theory of stability has been out- 

 lined there is ^ great deal of work to be done before the 

 results can be reduced to simple practical rules." 



\ FORM of cadmium cell suitable for supplying a small 

 current much more constant than can be obtained from a 

 storage cell is described by Mr. G. A. Hulett, of Princeton, 

 in the July number of the Physical Kevieui. A wide-necked 

 bottle of about 8 cm. diameter contains a layer of mercury 

 half a centimetre thick covered to a depth of 4 cm. or 

 5 cm. by a solution of 10 c.c. of strong sulphuric acid and 

 800 grams of cadmium sulphate crystals per litre of water. 

 A glass tray about 4 cm. diameter and 4 mm. deep is 

 supported in the solution a little above the surface of the 

 mercury, and contains the 12J per cent, cadmium amalgam. 

 Contact is made with the mercury and the amalgam by 

 means of wires enclosed in tubes. The mercurous sulphate 

 is prepared in the cell by sending a current through the 

 cell from the mercury to the amalgam, the solution being 

 kept well stirred during the process. The internal resist- 

 ance of such a cell is about 6 ohms, and it is capable of 

 giving a current of oooooi ampere for many days without 

 its electromotive force varying appreciably. A larger cell 

 has been used to give a constant current of 0-04 ampere 

 for a long period for bolometrical work. 



In the case of the majority of the ions Prof, .^rrhenius's 

 assumption that the mobility is independent of the con- 

 centration holds good through a considerable range of 

 dilute solutions, though variations occurring in stronger 

 solutions are well known, and have been investigated by 

 Jahn, by Bousfield, and by others. The hydrogen ion 

 appears, however, to be an exception. For some years 

 doubt has existed as to the correct value for its mobility, 

 transference experiments at moderate dilutions having 

 given a value 330, considerably higher than the value 315 

 deduced from conductivity measurements at extreme dilu- 

 tions. This discrepancy has been traced by Noyes and 

 Kato, who describe their observations in a recent number 

 of the Journal of the American Chemical Society, to varia- 

 tions in the mobility of the hydrogen ion occurring at 

 dilutions much greater than those at which the mobilities 

 of the other ions become constant. Concordant values 

 were obtained from independent observations with hydro- 

 chloric and nitric acids, and the evidence for the reality of 

 the variations of mobility appears to be complete. The 

 numbers given in the following table show the magnitude 

 of the changes involved : — 



„ . .. THNO., 0-058 0-0184 0-0067 0-0022 o 



Concentration ^j^(,, ^ ^'.^ ^.^^^^ ^.^^56 00021 o 



Mobihtv '^"^''-'^ 350-3 3402 339-1 332-2 3^4-6 



Mobility ...(^HCl 344-2 340-5 341-4 331-S 3240 



NO. 2026, VOL. 78I 



The Harben lectures of the Royal Institute of Public 

 Health, delivered by Prof. Paul Ehrlich last year upon 

 the subject of " Experimental Researches on Specific Thera- 

 peutics," have been published by Mr. H. K. Lewis, Gower 

 Street, in the form of a small volume, having a portrait 

 of the lecturer as a frontispiece. The price of the volume 

 is 25. 6d. net. 



For the third year in succession the Library Association 

 has published its " Class List of Best Books and Annual 

 of Bibliography." The work is a classified and annotated 

 catalogue of important works which appeared in the year 

 endedon June 30. The previous year's issue comprised 

 iSoo titles ; this year the number has risen to more than 

 2500. The publication should be useful both to the general 

 reader and the student as a guide to recent literature of 

 noteworthy value. 



The third edition of Prof. H. Snyder's " Soils and 

 Fertilisers " has just been published by the Macmillan 

 Co., New York. The second edition was reviewed in 

 Nature of January 18, 1906 (vol. Ixxiii., p. 266) ; and 

 though the work has been enlarged and revised, no further 

 description of its contents is necessary. It is sufficient 

 here to say that the book presents in a concise form the 

 scientific principles involved in the successful treatment of 

 the soil and the production of crops. 



OUR ASTRONOMICAL COLUMN. 

 ■luE Origin of ihe Recently Discovered Jovian 

 Saiellites.— Criticising Prof. Forbes's recent suggestion 

 (Naiure, p. 30, No. 201 1, May 14) that the newly dis- 

 covered eighth satellite of Jupiter may in reality be the 

 long-lost Lexell's comet of 177°. captured by the giant 

 planet in 1779, Prof. Tarrida del Marmol conjectures that 

 a more likely explanation of the origin of the sixth, 

 seventh, and eighth satellites is to be found in the sugges- 

 tion that they are asteroids which revolved at the same 

 distance from the sun as Jupiter, and were captured by 

 the latter. He shows that if the asteroid be either further 

 away from, or nearer to, the sun, the annexation cannot 

 take place, but when the distances are equal the asteroid 

 will, with its relatively negligible mass, be effectively 

 the inferior planet, and will suffer capture The recent dis- 

 covery of the four Jovian asteroids Achilles Patroc us. 

 Hector and 1908 C.S., strengthens the possibility of this 

 conjecture. Prof, del Marmol concludes his note which 

 appears in the August number of Knoivledge and niiis- 

 ^^^cTscientific N^ws (vol. v.. No. 8, p. 185), with the 

 tentative suggestion that the Saturnian satellites Hyperion 

 Themis, and Phoebe may have been captured by Saturn in 

 the same manner. , , ^ 



In answer to our inquiries concerning the above sug- 

 gestions, Mr. Melotte, the discoverer of J"?'^'^^/'^ Xe^ 

 satellite points out that the images found on the plates 

 tive no i^ication whatever of diffuseness, such as migh 

 be expected from a cometary body, but are in every respec 

 similar to the photographed images of the other a.nt 

 satellites. According to Hind, Lexell s _ comet, when 

 nearest the earth, exhibited a white -bulosity surrounding 

 the nucleus and subtending an angle of 2 23, although 

 no tail was visible. Mr. Melotte also suggess that others 

 of the nTajor planets may be attended by ^ateites hitherto 

 undiscovered by reason of their faintness, and tha the 

 motions of these may subsequently be found to be retro 

 grade, thus reducing ihe importance of the anomalies which 

 have hitherto nuzzled astronomers in considering the origin 

 of the satellites under discussion. In '^°"'^1"';°"'^ .^^^ 

 adds that possibly Prof, del Marmol intended to write 

 Tapetus in place of Themis, as, so far as is known, the 

 latter rarely reaches a distance of 220" from Saturn. 



Elements of the Oriut of Jufiter's Eighth Satellite. 

 -Circular No. .02 from the Kiel Centralstelle contains 

 the following equatorial elements for the orbit of Jupiter s 

 eighth satellTte, computed by Messrs. Crawford and Meyer 



