PHYSICS, PROGRESS OF, IN" 1901. 



may be of the character of a pressure. The hard- 

 ness of solid solutions i. e., of alloys will thus 

 be of the nature of an osmotic pressure, and this 

 conclusion explains the varied hardness of iron 

 when alloved with different metals. 



Viscosity. R. Reiger (Physikalische Zeit- 

 sehrift, Jan. 5), from a study of the "time of re- 

 laxation " in colophonium gelatin, and chilled 

 glass, finds that in their plastic state these sub- 

 stances show a relaxation in accordance with 

 Maxwell's theory, whereas in the hard state the 

 viscosity rises first to a maximum before relaxa- 

 tion sets in. With falling temperatures the time 

 of relaxation and the viscosity increase rapidly. 



Elasticity. M. Cantone and G. Contino (Nuo- 

 vo Cimento, 1900) have studied the influence of 

 traction and torsion on the red variety of caout- 

 chouc, and also its thermal expansion. As the 

 load increases there is an increase in the modulus, 

 and not a diminution as postulated by Villari 

 and Rontgen. This is opposed to the behavior of 

 the metals. As regards torsion, the material be- 

 haves in essentially the same manner as do the 

 hard metals. 'Rudeloff has investigated the in- 

 huence of heat on elasticity in cast iron, cast 

 steel, beaten bronze, and lead by bending and 

 stretching rods at various temperatures. Most 

 metals were found to be as strong for small loads 

 at fairly high temperatures as at low tempera- 

 tures; but for greater loads they are much 

 weaker. A. Gray, V. J. Blyth, and J. S. Dunlop 

 (Royal Society Proceedings, Oct. 31, 1900) have 

 determined the Young's and rigidity moduli of 

 metal wires at different temperatures between 

 that of the atmosphere and 100 C. German sil- 

 ver, mild steel, brass, copper (commercial), cop- 

 per (hard-drawn electrolytic), and soft iron were 

 tested. In determining the rigidity moduli by 

 the vibration method, the authors noticed that 

 the decrement of the vibrations appears to be a 

 function of the temperature and of the amplitude. 

 In German silver the decrement is smaller at the 

 high temperatures instead ' of larger as in the 

 others. A. Lafay (Annales de Chimie et de Phy- 

 sique, June) has measured the deformations of 

 two steel or bronze spheres in contact under dif- 

 ferent pressures ; also the deformations when a 

 sphere is in contact with a plane surface. Hertz's 

 mathematical analysis of the problem only im- 

 perfectly represents the real phenomena, and in 

 particular his conclusion that the diminution of 

 distance between centers of two bodies varies as 

 the two-thirds power of the pressure is only true 

 where the deformations are relatively large. The 

 divergence from theory becomes greater as the 

 deformations become less, notwithstanding the 

 fact that the theory is based on conditions of 

 small deformation. 



Rigidity. 1. C. Hebb (Transactions of the 

 Nova Scotian Institute, 10, pp. 273-286, 1900) has 

 confirmed the experiments of W. A. Macdonald 

 which show that the rigidity (kinetically de- 

 termined) of a fresh or partially fatigued vulcan- 

 ized rubber cord, when subjected to increasing 

 tension, at first diminishes, then reaches a mini- 

 mum, and finally increases. In the case of a 

 sufficiently fatigued cord, the minimum point 

 seems to disappear. Increase of tension in a 

 cord that has been stretched for some time imme- 

 diately decreases the rigidity, but if the cord is 

 left under the tension the rigidity increases again. 

 Polish. Rayleigh (Nature, Aug. 15) states 

 that with finely ground, as distinguished from 

 polished, glass surfaces, such fineness may be at- 

 tained that a candle is seen reflected at an angle 

 not exceeding 00, measured from the perpendicu- 

 lar. Such surfaces are still too coarse for per- 



pendicular specular reflection of the longest visi- 

 ble waves of light, although they are fine enough 

 to reflect without sensible diffusion the waves 

 one hundred times longer than those of red light. 

 The balance of evidence, however, indicates that 

 grinding and polishing are essentially different. 

 Jn grinding, the powder hits the surface, break- 

 ing out small fragments, while polishing is in all 

 probability a molecular operation, no coherent 

 fragments being broken out. In one case the 

 author finds that a thickness of about six wave- 

 lengths of mean light was removed during the 

 polishing of a piece of glass; in another case, with 

 very finely ground surfaces, polishing lowered 

 the mean surface two or three wave-lengths. 



Liquids and Gases. Kinetic Theory. Jeans 

 (Philosophical Transactions, May 22) notes that 

 if the mean kinetic energy is the same for each 

 degree of freedom as postulated in the Maxwell- 

 Boltzmann theory of gases, results follow which 

 are irreconcilable with experiment. But he re- 

 marks that Boltzmann's law of distribution of 

 energy is proved to be the necessary law only if 

 certain conditions postulated by Boltzmann are 

 fulfilled. It fails altogether if there be dissipa- 

 tion, even though the conditions in other respects 

 are fulfilled. There is dissipation if we admit any 

 interaction, however small, between molecules and 

 the surrounding ether. That such interaction ex- 

 ists is proved by the phenomena of radiation. He 

 finds that the second law of thermodynamics will 

 not generally hold for a gas emitting radiation. 



Solution. L. Bruner and S. Tolloczko (Zeit- 

 schrift fur Physikalische Chemie, Nov. 2, 1900), in 

 experiments with gypsum, acetanilid, phenyl- 

 acetic acid, phenylpropionic acid, and benzoic acid, 

 have confirmed the formula of Noyes and Whit- 

 ney, according to which the velocity of solution 

 is logarithmic. In addition, they have determined 

 the value of the constant per square centimeter 

 of surface. The system, solid substance unsatu- 

 rated solution, is considered to be practically un- 

 realizable, and the solid substance is regarded as 

 being in contact with a layer of saturated solu- 

 tion from which diffusion takes place into the 

 surrounding liquid. The constants found are 

 therefore diffusion constants. N. Schiller (An- 

 nalen der Physik, May 29), in a thermodynamical 

 investigation of the saturated solutions as modi- 

 fied by varying external conditions, shows that 

 when a single substance is in solution, external 

 pressure in general promotes solution and in- 

 creases the osmotic pressure. Where two fluids 

 dissolve into one another and form two saturated 

 solutions the effect of the external pressure in 

 general depends on the relative quantities of the 

 two fluids. Guinchant (Comptes Rendus, Feb. 

 25) has sought an expression for the variation 

 of the volume of a dissolved body with pressure. 

 Defining the volume of the dissolved body as the 

 difference between the volume of the solution and 

 that of the solvent, the author finds that it is 

 independent of the pressure, at least up to 4 

 atmospheres. The variation of volume which Ac- 

 companies the simple solution of a body in water 

 must then be due to a variation in the state of 

 aggregation of the solvent rather than to the 

 volume occupied by the dissolved molecules. F. 

 G. Donrian (Philosophical Magazine, June) ex- 

 plains colloidal solutions by means of Laplace's 

 theory of intermolecular attraction. Any small 

 volume-element in the bounding interface of a 

 solid immersed in a liquid is acted on by two 

 forces, one due to the attraction of the solid, and 

 the other to that of the liquid. For crystalline 

 solids the former is greater than the latter, while 

 for colloidal matter in contact with certain liq- 



