618 



PHYSICS, PROGRESS OF, IN 1893. 



Concentration of Energy. G. J. Stoney ("Phil- 

 osophical Magazine,'' April) remarks that if the 

 universe is permanent, concentration of energy 

 must go on somewhere to balance the dissipation 

 of energy which we know to be continually tak- 

 ing place. He suggests that microbes may be 

 its agents, as would be the case if they would 

 assimilate only the swiftest of the moving mole- 

 cules, thus continually sorting these out like the 

 hypothetical " demons " of Clerk Maxwell. 



Kinetic TJieory. Prof. L. Boltzmann (ibid., 

 March), in discussing the equilibrium of vis viva 

 in a gas, proves that the mean kinetic energies of 

 a shell and an atom are equal, and Maxwell's law 

 of the distribution of velocity between shells and 

 atoms is thus satisfied without assuming im- 

 pacts of shells and atoms on each other. If cer- 

 tain forms of central motion are suddenly dis- 

 turbed by collisions, the same will be produced 

 equally often elsewhere. 



Heat. Thermometry. E. II. Griffiths and J. 

 M. Clark (Cambridge, England, Philosophical So- 

 ciety, Oct. 31), following the suggestion of Dewar 

 and Fleming that the electrical resistance of a 

 metal disappears at the absolute zero, find by 

 extrapolation from the scale of a platinum ther- 

 mometer that R = at the mean value 273'86. 

 This agrees nearly with Joule and Thomson's 

 thermodynamic value for absolute zero, which is 

 273-7. They suggest that these data be used 

 in the graduation of a class 01 thermometers. 



Specific Heat. W. Voight (Wiedemann's 

 " Annalen," No. 8), in a series of determinations of 

 the physical constants of metals that have been 

 subjected to the minimum possible amount of 

 manipulation, finds that the specific heat of such 

 metals especially differs from that of drawn 

 and rolled metal. 



Radiation. B. Galitzin (ibid., 47, 1892) finds 

 that the transfer of energy to new masses of 

 ether is accompanied by expenditure of work in 

 the case of reversible operations, and that in the 

 case of adiabatic and reversible processes the 

 amount of disposable energy is inversely pro- 

 portional to the cube root of the volume 

 throughout which this energy is distributed. 



Mechanical Equivalent. E. H. Griffiths (Lon- 

 don Royal Society, Feb. 16) has endeavored to 

 secure great accuracy in the determination of 

 this constant by using a calorimeter that was 

 practically suspended in the bulb of a huge 

 thermometer, containing 70 pounds of mercury 

 and showing a change of 1 centigrade by a rise 

 of '300 millimetres. He finds that J=427'45 

 kilogram metres in the latitude of Greenwich. 



Conductivity. It has been generally supposed 

 that freedom from convection currents in meas- 

 uring the conductivity of liquids was insured 

 by letting the flow of heat take place from above 

 downward, but R. Wachsmuth (Wiedemann's 

 " Annalen ") shows that this is by no means the 

 case, using a solution of blue iodide of starch, 

 which is decolorized by heat. He observed in 

 the liquid strata with wavy outlines, in some 

 cases cooler at the top than at the bottom, and 

 obtained evidences of vortex motion. It seemed 

 impossible to avoid these movements in the 

 liquid. 



Temperature, of Vapor. Sakurai (" Journal of 

 the Chemical Society," June. 1892) has estab- 

 lished the fact that the vapor from a boiling salt 



solution has exactly the temperature of the solu- 

 tion, instead of that of the boiling point of pure 

 water, as was formerly believed. 



Sound. Photography of Sound Waves in Air. 

 C. Vernon Boys, in experiments having pri- 

 marily for their object the photography of a 

 moving rifle bullet, has obtained interesting 

 records of the accompanying aerial waves. His 

 apparatus, which was a triumph of delicate and 

 ingenious construction, worked on the principle 

 of making the bullet close an electric circuit in 

 its flight, causing a spark to pass just as the 

 bullet passed in front of the camera. The re- 

 sulting photograph was really that of the bul- 

 let's shadow, being perfectly black. The air 

 waves left their trace by refracting the trans- 

 mitted light just at the crest where the variation 

 of density was greatest. No waves at all ap- 

 peared when the velocity of the bullet was less 

 than the velocity of sound in air, and the in- 

 clination of the wave front to the vertical in- 

 creased with the velocity of the bullet, both 

 these facts being analogous to those observed 

 when an object travels through water. See the 

 illustration, which is a reproduction of one of 

 Prof. Boys's photographs. Dr. Raps (Berlin 

 Physical Society, Oct. 20) has gone further and 

 photographed the vibrations in organ pipes, not 

 directly, but by means of the displacement 

 caused by the waves in a series of interference 

 bands from an interference refractometer (see 

 LIGHT, below). The results, as recorded on a 

 moving sensitized surface, show sine curves cor- 

 responding to the fundamental when the pipe is 

 sounded gently. When it is blown harder, har- 

 monics appear superimposed on this, and finally 

 the harmonics alone appear. Dr. Raps has also 

 shown by this method the characteristic over- 

 tones of each vowel as they appear when sung. 



Vibrating Strings. The experiments of Raps 

 and Menzel (" Annual Cyclopaedia," 1892, p. 637) 

 have shown in their photographic records of the 

 movements of strings that during part of the 

 vibration the velocity of the strings is constant, 

 while during another part they are practically at 

 rest, the photographs showing zigzag lines with 

 straight, flat portions at top and bottom. 



Motion of Sound Waves. C. V. Burton (Lon- 

 don Physical Society, Feb.24) shows that always 

 in the case of plane waves, and in all practically 

 possible conditions in spherical waves, the mo- 

 tion involves a surface of discontinuity. If the 

 front of an air disturbance is produced by an 

 impulsion from a moving source, the wave front 

 always moves faster than the source, even if the 

 latter is moving faster than a feeble sound. 



Light. Diffusion. Chr. Wiener (Wiede- 

 mann's ' Annalen," 12), in experiments on diffu- 

 sion by rough surfaces, finds that Lambert's law 

 that the brightness of the surface is independent 

 of the angle is not strictly correct, the bright- 

 ness at the edge of a rough surface being only 

 six tenths that given by the law. At greatest 

 brightness the angle of incidence exceeds that 

 of reflection. W. E. Sumpner (London Phys- 

 ical Society, Dec. 9) thinks that the influence of 

 diffusion in increasing the illumination of rooms 

 and open spaces has not been sufficiently ap- 

 preciated. In general, the light from the walls 

 is Tnuch more important than that received di- 

 rectly, being in some cases twice as great. Ex- 



