PHYSICS. PROGRESS OF, IX 1896. 



630 



the viscosity is found to increase with the molec- 

 ular weight", and the more symmetrical the mole- 

 cule i if an isujncric compound, the lower the vis- 

 cosity. 



Diffusion of Ifefab. Roberts- Austen, in his 

 Bakerian Lecture before the London Royal Society 



- iencc." June 5). describes his experiments on 

 the diffusion of one metal in another. For molten 

 metals tin- " dillusivity " measured in square centi- 

 metres a day is a- ful. 



Gold in lead 3'19 at 500. 



" bismuth 4'.VJ 



- - tin 4-0.-1 ' 



Silver in tin 4'14 



Lead in tin 3".S 



Rhodium in lead 3'04 ' 



Platinum in lead 1'69 " 490 



Gold in lead *"* " 



Gold in mercury '~2 " 11 



For solid metals the results are as follow : 



Diffusivity of gold in fluid lead at 550 3" 19 



solid " 251 0-03 



200 0007 



165 O-i i' >4 



100 000002 



Fluid Friction. Umani (' Xuovo Cimento ") 

 concludes from experiments on mercury and nickel 

 that finite slipping takes place, in this case at least, 

 at the surface of a solid in contact with a liquid a 

 vexed question in the theory of fluid friction. 



Capillarity. Linebarger (" American Journal of 

 Science,'' August) has devised an apparatus for the 

 rapid determination of the surface tensions of 

 liquids, based on Jager's method of immersing two 

 capillary tubes of different bore and measuring 

 the difference of the depths to which they are 

 plunged when the forcing out of air bubbles at 

 the bottom requires the same pressure in both. 



<'ttion. Palmer ("American Journal of 

 Science," October) finds that in a vertical steam jet 

 the surface that separates the invisible from the 

 visible part is sharply marked and oscillates up and 

 down. The demarcation seems to be due to the 

 fact that the instantaneous heat of condensation 

 can superheat the supersaturated steam as it arrives 

 at the surface. The velocity of condensation in- 

 creases with the pressure, aud the amplitude of the 

 oscillations decreases with it. 



Critical State. Barns (" American Journal of 

 Science," July) regards his experiments as proving 

 that there is no "real continuity between COi gas 

 and CO a liquid at the critical temperature. There 

 is continuity between the liquid and a gas which 

 preserves the same molecule, the same molecular 

 structure as the liquid from which it issues. Doubt- 

 less at still higher temperature the gas with the 

 liquid molecule will break up into the true gas with 

 the gaseous molecule." 



Impact with a Liquid Surface. Worthington 

 and Cole (London Royal Society, Dec. 12. 1895) have 

 studied this phenomenon by means of instantaneous 

 photography, and have thereby added much to the 

 accuracy and fullness of detail of our knowledge of 

 what takes place during a " splash." 



Flotation <tf Jfetals. Mayer ("Science." Sept. 4) 

 finds that rings of metal wire, highly polished and 

 chemically clean, will float on water. He regards 

 the phenomenon as dependent on the condensation 

 of a film of air on the metallic surface, for if one of 

 the rings be heated and placed on the water as soon 

 as it is cool it sinks at once. 



<i;i>ps. Kinetic Theory. Bertrand (Paris Acad- 

 emy of Sciences. May 4). after a critical examination 

 of Maxwell's formula for the relation between the 

 velocities of the gaseous molecules and their compo- 

 nents in any arbitrarily chosen direction, concludes 

 that it is absurd, since it gives an apparent solution 

 of a problem that is, from its nature, insoluble. M. 



Bertrand points out that Maxwell, in finding the law 

 of distribution of speed in a syMi-ni of m*.;. -rules, 

 assumed that the velocity in any direction was in- 

 dependent of that in any perpendicular direction. 

 This assumption M. Her: rand regards as unjustifi- 

 able. Boltzmann (Wiedemann'a Annalen." May) 

 regards the Boltzmann-Maxwell law as a theorem 

 in probability rather than a principle of abstract 

 dynamics, there being nothing to preclude the pos- 

 sibility of the molecules behaving at any instant in 

 a manner quite different from that indicated by 

 the law, although the greater the number of mole- 

 cules the more improbable does such a departure 

 become. Tait (Edinburgh Royal Society. June 15), 

 in a defense of Maxwell's proof against Hertrand's 

 attack, asserts that the proof involves none of the 

 absurdities charged against it. The gist of the 

 matter, in his words, is this: "There is a unique 

 solution of the problem : Maxwell's is one solution, 

 therefore it is the solution. Del Lungo (Atti dei 

 Lincei) asserts that the independence of distribu- 

 tion of velocities assumed by Maxwell in his proof 

 is a necessary consequence 'of the conservation of 

 momentum and of energy. The distribution in 

 question, he says, satisfies many conditions that are 

 not satisfied by any other, and that represent closely 

 the phenomena of gases. 



Viscosity. Xoyes and Goodwin (" Physical Re- 

 view. 1 ' Xovember-December) conclude, from experi- 

 ments on the viscosity of mercury vapor, that the 

 space occupied by a molecule is of the same order 

 of magnitude as that occupied by an atom, so that 

 viscosity can not be used to determine molecular 

 complexity. 



Velocity in Tubes. Bazin (Paris Academy of 

 Sciences, June 1) finds from experiments that no 

 single expression can be found that will accurately 

 represent the velocity of an air current at any given 

 point between center and circumference of a tube. 

 At a distance from the center equal to three fourths 

 of the radius, the velocity is equal to the mean for 

 the whole tube. 



Barometry. Hefner-Alteneck (Berlin Physical 

 Society, Dec. 13, 1895) has devised an instrument 

 for demonstrating minute changes in atmospheric 

 pressure, which is said to be 150 times more sensi- 

 tive than a mercury barometer. It consists of a 

 flask whose neck communicates with a horizontal 

 gla-s tube. The central part of the tube, which 

 bends slightly downward, contains an index of 

 colored petroleum, which moves at the slightest 

 change of external pressure. 



Acoustics. Variation of Intensity with Distance. 

 Shaefer (Wiedemann's "Annalen," April) has 

 proved, by attaching a telephone to a clock and 

 bringing it to different degrees of sensitiveness, that 

 sound does not diminish in intensity strictly with 

 the square of the distance, but at first more slowly 

 and then more rapidly. 



Sensitive Flames. Bouty (Paris Academy of 

 Sciences, Feb. 1?) has shown that the nature of the 

 gas that is used affects the sensibility of a sensitive 

 flame to sound. For instance, that of a pure hydro- 

 gen flame, which is small, can be increased by ad- 

 dition of an inert gas. such as nitrogen or carbon 

 dioxide. Jastrow ( Science." April 10) uses for the 

 study of sound intensities in his psychological lab- 

 oratory a singing flame whose intensity can be 

 regulated very delicately by means of a supply 

 valve bearing an index that magnifies the change 

 in the height of the flame 100 times. Hallock, by 

 photographing sensitive flames that are set in vibra- 

 tion by resonators, has been able to obtain a very 

 perfect registration of compound tones, with all 

 their characteristics. He believes that he has 

 proved by this means that the human voice is anal- 

 ogous to "a stringed rather than to a reed instru- 



