726 



PHYSICS, PROGRESS OP, IN 1891. 



claims to have measured the time of a revolution 

 to within -0002 of a second. 



Force and Determinism. An interesting dis- 

 cussion in " Nature," participated in by C. 

 Lloyd Morgan, E. T. Dixon, and others, was 

 called forth by a statement of Prof. Oliver J. 

 Lodge that no energy is expended in changing 

 the direction of a body's motion, and by his sug- 

 gestion that the explanation of the control of 

 matter by mind is to be found in some such 

 direction. 



Pressure. L. Cailletet (Paris Academy of . 

 Sciences, April 13) describes the huge manometer 

 which has been constructed at the Eiffel Tower. 

 It is more than 900 feet long, and can measure, 

 by the simple weight of its liquid column, a 

 pressure of 400 atmospheres. The tube is of 

 steel, but at distances of 3 metres stop-cocks 

 connect with glass tubes 3 metres long, en- 

 abling the exact height of the column to be read 

 off when desired. 



Liquids. Solution. The battle between the 

 adherents of the rival theories of solution ('"An- 

 nual Cyclopaedia," 1890, p. 711) still goes on. 

 James Walker, in a review of the situation 

 (' Philosophical Magazine," October), concludes 

 that the hydrate theory is no longer a serious ri- 

 val of the osmotic, the list of whose achieve- 

 ments is constantly increasing. Sidney Lupton 

 (ibid., May) examines the methods of Mendeleef, 

 S. U. Pickering, and other advocates of the hy- 

 drate theory, and asserts that though the accuracy 

 of these methods is great, it is not so great as to 

 warrant their conclusions. He objects particu- 

 larly to the method of drawing graphic curves 

 by laths or flexible rulers. Prof. Pickering de- 

 fends his methods and results in the issue for 

 July, and E. II. Hayes justifies the " lath " 

 method by an elaborate mathematical investiga- 

 tion. Prof. Orme Masson, at the January meet- 

 ing of the Australasian Association for the Ad- 

 vancement of Science, read a notable paper in 

 extension of the osmotic or gaseous theory. If 

 a solid be heated in a vacuum it first vaporizes, 

 then melts, the liquid continues to vaporize, and 

 finally above the critical point vapor and liquid 

 become homogeneous. So it is, says Prof. Mas- 

 son, with a solid and a pure solvent. First the 

 solid begins to dissolve, then it melts, and the 

 liquid continues to dissolve ; finally, at a certain 

 temperature, the liquid and its solvent become 

 homogeneous. This analogy, he claims, is borne 

 out by facts. His final conclusion is that 

 in every system of solution that starts with a 

 solid and a simple solvent, the solid has a " so- 

 lution melting-point" lower than its true melt- 

 ing point. Above this two liquid layers exist, 

 each having some of the other in solution. 

 These become homogeneous at a temperature de- 

 pending on the ratio of the original ingredients. 

 One ratio demands a higher temperature than 

 any other, and this is the " critical solution tem- 

 perature," above which either ingredient is infi- 

 .nitely soluble in the other. Prof. Ramsay (Lon- 

 don Royal Society, March 5) extends these ideas 

 still further. Masson considers only isobaric 

 curves. If isothermal curves be considered, per- 

 haps, on increasing concentration by eliminating 

 one solvent, the other would not separate visibly, 

 but the two would remain mixed till one had 

 been entirely removed. In "Nature" (March 



26) Prof. S. U. Pickering criticises Masson's 

 views, and concludes that the existence of a 

 " critical solution temperature " should follow 

 also from the hydrate theory. He objects espe- 

 cially to the word " pressure " as used by the 

 osmotists. Messrs. Wanklyn, Johnstone, and 

 Cooper (" Philosophical Magazine," November) 

 hold that true physical solution includes only 

 cases where there is no change of volume, 

 such as that of sugar and water, and that where 

 there is a change of volume, however slight, 

 there is always chemical action. Carl Barus, of 

 the United States Geological Survey (" American 

 Journal of Science," February), discusses the so- 

 lution of glass by pure hot water. The solubil- 

 ity is very great at 185 C., and up to this point 

 a mixture of glass and water shrinks by solution 

 more than 11 per cent. The effect of solution 

 is to increase the compressibility. He thinks 

 the solubility of glass is due to the instability of 

 the glass molecule, and concludes that, in many 

 instances, a definite dissociation temperature of 

 the solid must be surpassed before solution sets 

 in. In the same journal (November) Dr. Barus 

 describes similar experiments on vulcanite, 

 which, he thinks, prove that it acts in the same 

 way. This substance has not heretofore been 

 dissolved so perfectly that it could be regained 

 in a solid form, but Dr. Barus has so dissolved it in 

 carbon dioxide, chloroform, the paraffine series, 

 aniline, benzol, and some of the ethers. Vul- 

 canite newly deposited from solution shows curi- 

 ous phenomena of slow elasticity. A stretched 

 thread shortens again very slowly and a twisted 

 thread squirms about like a worm for several 

 minutes. Dr. Barus thinks, however, that the 

 thin solutions of vulcanite are not true solutions, 

 for in sealed vessels they become gelatinous in 

 time. Hofmeister ("Archiv fiir Experimental 

 Pathologic ") has investigated the swelling of 

 gelatin in solutions. In pure water the effect is 

 less than when some salt is present. He considers 

 the forces involved to be similar to those shown 

 in the absorption of gases by liquids and solids. 



Osmosis. Boltzmann (" Journal of the Chem- 

 ical Society," April) has investigated osmotic 

 pressure mathematically from the standpoint of 

 the kinetic theory of gases. He finds that the 

 osmotic pressure equals the gaseous pressure 

 that the dissolved substance would exert if it 

 were distributed as a gas through a volume 

 equal to that occupied by the solvent. He as- 

 sumes that the mean kinetic energy of the dis- 

 solved molecule equals that of the gas molecule 

 at the same temperature. Nernst (Berlin Chemi- 

 cal " Berichte," November, 1890) points out that 

 a layer of water between two layers of benzol 

 dissolved in ether acts precisely like a mem- 

 brane. Ether will dissolve in water, but benzol 

 will not ; so, if the two solutions are of unequal 

 strength, osmosis of the ether will take place till 

 they are equally strong. 



Capillarity. Experiments similar to those of 

 Lord Rayleigh (''Annual Cyclopaedia," 1890. p. 

 711) have been made by Miss, Agnes Pockels 

 ("Nature," March 12). She finds that if a strong- 

 ly contaminated liquid surface be gradually ex- 

 tended, the surface tension at first varies, but 

 finally becomes constant. She calls the former 

 state the " anomalous " and the latter the " nor- 

 mal " condition of the surface.' Every solid 



