PHYSICS, PROGRESS OF, IN 1890. 



713 



searches on this subject and which do not alto- 

 gether agree with them. He has shown that 

 when two simple tones interfere two sets of pri- 

 mary beats are produced, " inferior " and " su- 

 perior," corresponding to the positive and nega- 

 tive remainders obtained by dividing the fre- 

 quency of the higher tone by that of the lower. 

 Thus, if the frequencies are 74 and 40, the beats 

 are 34 and (5 per second, since we may say that 40 is 

 contained in 74 once with a remainder of 34, or 



twice, with a remainder of 6. He has shown 

 that the so-called combinational tones are due to 

 the coalescence of beats. By his " wave siren " 

 he proves also that the difference of phase of the 

 elements of a compound note affects its timbre. 

 In this siren a toothed cylinder revolves before a 

 vertical slit through which a stream of air passes. 

 The intensity of the sound varies- according to 

 the shape of the teeth, and by shaping them 

 properly the timbre of any compound note can 

 be imitated. It is found thus that the sound 

 of two notes differing in phase by one quarter is 

 distinctly more forcible than that of the same 

 notes differing by three quarters. 



Voice figures. This name is given by Mrs. 

 Watts Hughes to what are practically Chladni's 

 figures in a viscid medium. A semi-fluid paste 

 is spread on an elastic membrane which is made 

 to vibrate by a steadily sung note. The paste is 

 thrown into beautiful forms that resemble waves, 

 flowers, and trees. In one set of figures, called 

 by Mrs. Hughes "daisy forhis," the number of 

 petals increases as the pitch rises. 



Heat. Thermometry. The experiments of 

 Dr. Sydney Young show that the main part of 

 the observed permanent ascent of the zero point 

 of a mercury thermometer, after prolonged heat- 

 ing, is not due to compression of the bulb, as has 

 been supposed. H. Tomlinson supposes that the 

 molecules of all solids, after heating nearly to 

 the melting point, are, after cooling, in a state of 

 constraint. This state would be abolished by re- 

 peated heating and cooling, the particles, by 

 what Prof. G. Wiedemann calls "accommoda- 

 tion," settling into their normal positions. Young, 

 however, says that long-continued steady heating 

 is more effective. J. Puluj has invented a new 

 telethermometer, which has a glass tube of hy- 

 drogen, in which is a carbonized thread fastened 

 to an iron spiral. These form two branches of a 

 Wheatstone's bridge. When the temperature 

 changes, the resistances of the two substances 

 change in opposite directions, destroying the 

 balance and affecting a galvanometer at any dis- 

 tance. The instrument will show a change of 

 0-1 C. 



Heat of Vaporization. E. Mathias, from ex- 

 periments on carbon dioxide near its critical 

 point, finds that if a curve be constructed with 

 temperatures as abscissae and heats of vaporiza- 

 tion as ordinates, its tangent at the critical point 

 is vertical, making it probable that the latent 

 heat vanishes altogether at the critical point. 



Boiling Points. Carl Barus, of the United 

 States Geological Survey (" Philosophical Maga- 

 zine," February), has determined the pressure 

 variations of certain high temperature boiling 

 points. In the equation of Dupre, log p=A 

 B/0 C log 0, where is the boiling point and p 

 the pressure, he has found the values of the 

 quantities A, B, and C, for several substances. 



C was practically constant for all. Assuming it 

 to be absolutely so, the results were: 



The same experimenter(" Philosophical 

 zine," October) thinks that whenever a substance 

 passes from the liquid to the gaseous si site, no 

 matter whether above or below the critical point, 

 the cause is a change of the molecule from a 

 more complex to a less complex form. So long 

 as the molecule is unchanged, the isometrics 

 (lines of equal volume) are all straight lines, but 

 as soon as the change begins they curve. He 

 remarks, however, that pressures that seem very 

 large to us may be infinitesimal compared with 

 the molecular pressures in liquids and solids. 



Energy of a Gas. G. Staub compares this 

 quantity with the light the gas is capable of 

 emitting, by placing a Geissler's tube in an ice 

 calorimeter. The ice transmits the luminous 

 rays, so that only the energy of the dark ones is 

 measured. The measurement is then repeated 

 with the surface of the tube blackened so as to 

 absorb all rays. The maximum of light was 

 found to be 10 per cent, of the total energy, 

 which rose to 32'8 per cent, when condensers 

 were used. In hydrogen the optical effect was 

 less than in air. 



Kinetic Theory. E. P. Culverwell ("Philo- 

 sophical Magazine," July) grants Sir William 

 Thomson's objection to the kinetic theory. 

 That objection is that mutual action of mole- 

 cules, mathematically considered, does not tend 

 to establish temperature equilibrium. Culverwell 

 says, however, that owing to the impossibility of 

 excluding the action of the ether, it can never be 

 proved that the unaided gas molecules do tend 

 practically to this result. He regards the actual 

 tendency to uniform heat as an action of the 

 ether analogous to conduction. This assump- 

 tion reduces the number of facts explicable by 

 the pure kinetic theory, by shifting the trouble 

 to the ether. Ladislaus Xatanson (" Philosophi- 

 cal Magazine," January) remarks that in the 

 kinetic theory we are far from possessing a gen- 

 eral definition of temperature, the usual one be- 

 ing applicable only to perfect gases. In cases 

 where atoms and molecules both exist in a gas 

 the mean values of the kinetic energies of the 

 two classes may be different, and not even in 

 constant ratio. Which should measure the tem- 

 perature? It seems necessary to suppose that 

 iodine atoms, N0 ? groups, etc., combine into 

 molecules only during collision, and this is prob- 

 ably true of all gaseous molecules. 



Light. Velocity. Prof. E. W. Morley finds 

 that the velocity of light increases in a magnetic 

 field by 7 parts in 1,000,000,000. 



Measurement by Light Waves. Prof. A. A. 

 Michelson (" American Journal of Science," 

 February) concludes from experiments with the 

 refractometer that with a few pieces of plane 

 glass it is possible to construct an instrument 

 that combines the functions of a microscope, 

 telescope, and spectroscope, and that, for pur- 

 poses of measurement, it may be made far to 



