PHYSICS, PROGRESS OF, IN 1898. 



any of the methods of rational mechanics, for tin- 

 very troublesome characteristic of all unstable states 

 of a system is that subsequent aspects of the system 

 are influenced to a finite extent by infinitesimal 

 initial causes. He concludes that the law of veloci- 

 ty as related to temperature with at least two pipes 

 of different roughness, as well as that connecting 

 velocity with radius, needs further experimental in- 

 vestigation. Hele-Shaw (Institution of [British] 

 Naval Architects, July, 1897. and April, 1898) shows 

 that the flow of water in two dimensions past va- 

 rious cylindrical and prismatic obstacles can be in- 

 vestigated experimentally by using water containing 

 air flowing between parallel glass plates. The air 

 makes the water turbulent where the flow is most 

 rapid. His photographs show in every case a clear 

 line around the boundary, indicating that a thin 

 film there remains comparatively calm, while shear- 

 ing motion takes place in it. They also show "dead 

 water" behind blunt edges, confirming the view 

 that to minimize resistance a solid must taper at 

 the stern rather than at the bow. The stream lines 

 shown in the experiments coincide with those cal- 

 culated mathematically for a perfect liquid, not- 

 withstanding the difference in conditions. Prof. 

 Shaw's work has been praised by some as the first 

 to make hydrodynamics an experimental science. 

 Others criticise it as dealing with a mixture of 

 water and air instead of with pure water. 



Diffusion. Griffiths (London Physical Society, 

 June 10), in experiments on diffusive convection or 

 currents in a liquid caused by variations in the 

 quantity of dissolved substance, finds that when 

 two tubes of slightly different lengths unite an up- 

 per compartment filled with water to a lower one 

 filled with a solution of copper sulphate, this kind 

 of convection occurs up the longer tube and down 

 the shorter, while diffusion takes place up both. 



Absorption. Vignon (Paris Academy of Sciences, 

 July 4) finds that textile fabrics have specific ab- 

 sorptive powers for each liquid. Silk has the high- 

 est, wool is nearly equal to it, and cotton falls con- 

 siderably below. Physically, textiles should be 

 regarded as porous bodies ; their absorptive power 

 for water is about equal to that of a large sponge. 



Condensation. Wilson (Cambridge [England] 

 Philosophical Society, Jan. 24) finds that ultra-violet 

 light focused in moist dust-free air determines con- 

 densation as a bluish fog. If substances opaque to 

 the rays are interposed there is no condensation. It 

 is possible that the small particles to which the blue 

 of the sky is due result from this action. 



Solution. Van der Lee (Amsterdam Academy of 

 Sciences, Oct. 29) finds that the critical temperature 

 of solution of a mixture of phenol and water ap- 

 pears to rise with increased pressure. Experiment 

 confirms the theoretical indication of a maximum 

 in the line that shows the pressure of the vapor in 

 contact with the liquid as a function of the compo- 

 sition. Lehfeldt (London Physical Society, Nov. 25) 

 finds that the same pair of liquids is completely mis- 

 cible above 68 C., and incompletely below that tem- 

 perature. At temperatures not too close to the criti- 

 cal point the vapor pressure of a saturated mixture 

 is approximately the sum of the partial pressures 

 calculated for the two saturated solutions. The au- 

 thor states that normal organic liquids always mix 

 completely, but according to Prof. S. Young (ibid.) 

 there are pairs of such liquids that approximate 

 closely to partially miscible liquids, as benzene and 

 normal hexane. Traube (Berlin Chemical Society, 

 February) concludes that the contraction that takes 

 place on the solution of a substance in water is 

 proportional to the concentration of the solution 

 and almost independent of the nature of the dis- 

 solved substance. In aqueous solutions he believes 

 it due to the attraction between the solvent and the 



dissolved substance. The number of water particles 

 with which a given molecule of a substance in di- 

 lute solution combines is equal for all non-electro- 

 lytes, and for electrolytes increases proportionally 

 to the number of ions. Van't Hoff's law of osmot- 

 ic pressure may be deduced from this if we suppose 

 that a molecule of any non-electrolyte in any dilute 

 solution is at any moment united with only one 

 particle of the solvent. 



Hi/drometry. O'Toole (Dublin Royal Society) has 

 devised a new form of hydrometer in which between 

 the floating bulb and the weight pan there is what 

 he calls a " standard bulb." The weights required 

 to alter the immersion of the instrument from a 

 point below to a point above this bulb equal the 

 weight of its volume of the liquid. 



Sedimentation. Spring (Belgian Royal Academy) 

 finds that pure water holding in suspension finely 

 divided silica, or other non-electrolytic matter, be- 

 gins to clear gradually when two platinum elec- 

 trodes are plunged into it and a current is passed 

 through them. He asserts that the turbulent state 

 is due to a modification of the electric state of the 

 particles caused by the change in the energy of at- 

 traction of the matter forming them, consequent 

 on disintegration. 



Crystallization. Friedlander and Tammann 

 (" Zeitschrift fiir physikalische Chemie ") find that 

 the speed of solidification (the speed of propagation 

 of the separating layer between liquid and solid 

 when a liquid is in a state of superfusion), while it 

 increases at first proportionally to the degree of su- 

 perfusion, as shown by Gernez, afterward attains a 

 value which it maintains for a long time and finally 

 decreases again with further increase of the super- 

 fusion. Every substance has its own curve denot- 

 ing its behavior under these circumstances. 



Uases. Waves of Explosion. Violle (Paris Acad- 

 emy of Sciences, Jan. 8). in experiments on the ve- 

 locity of the wave produced by exploding powder 

 and mercury fulminate in a steel tube, finds that as 

 initial condensation increases the mean velocity of 

 propagation also increases from that of sound up to 

 about four times that speed. Jones and Bower 

 (Manchester Literary and Philosophical Society, 

 Jan. 25). from investigations on the collision of two 

 explosion waves, believe they have proved that there 

 is an increase of pressure at the point of collision. 

 This is established by hydraulic tests, by photo- 

 graphs, and by the increase of luminosity at the 

 point of collision, as well as the fact that the speed 

 of the reflected wave is greater than if it had been 

 reflected from a hard surface. 



Mixtures. Leduc (Paris Academy of Sciences. 

 Jan. 17) proposes to replace Dalton's law (that the 

 pressure of a mixture of gases is the sum of the 

 pressure due to each) by another to the effect that 

 the volume occupied by such a mixture equals the 

 sum of the volumes that the components would 

 occupy at the same temperature and pressure. These 

 two laws are equivalent only when Boyle's law 

 holds exactly. 



Expansion. Teudt ("Zeitschrift fiir physika- 

 lische Chemie," XXVI, 113) has studied a curious 

 deviation of atmospheric air from Gay-Lussac's 

 law, the expansion above 350 C. being 'excessive. 

 The deviation from the law is 2 per cent, at' 400 

 and 3 per cent, at 450% and is due to nitrogen alone. 

 The author suggests that this gas exists in the at- 

 mosphere in an allotropic form, which is changed to 

 the ordinary form at high temperatures. 



Acoustics. Velocity. Leduc has objected to the 

 common method of measuring the velocity of sound 

 in air. owing to the presence of moisture, but Violle 

 (Paris Academy of Sciences, Dec. 5) shows that the 

 correction due to this is smaller than the experi- 

 mental error of the measurements. 





