640 



PHYSICS, PROGRESS OF, IN 1896. 



ment. His device may be used in tone analysis, 

 and may become a useful adjunct in voice culture. 



Resultant Tones. Everett (London Physical So- 

 ciety, Jan. 24) has propounded a new theory of re- 

 sultant tones, depending on the fact that while by 

 an analysis of a periodic curve compounded of two 

 simple harmonic motions, only two terms of a 

 Fourier scries are obtained, if some error has been 

 made originally in adding the motions, which error 

 is repeated for each wave, then a third term ap- 

 pears, having a frequency that is the greatest com- 

 mon measure of the original two. The "error" in 

 the acoustical case, Prof. Everett supposes to occur 

 during the transmission of the sound by the ossicles 

 of the ear. The theory is supported by the fact 

 that in the violin, where the sound post transmits 

 the sound in some respects like the ossicles, it is 

 easy, by sounding two strings, to obtain tones that 

 agree with the hypothesis. 



Heat. Thermometry. Fessenden (" Nature," Jan. 

 16) describes a new method of measuring tempera- 

 ture, which he has used for several years. He uses 

 two thermo-j unctions, one in the substance whose 

 temperature is to be measured, the other in the 

 bulb of an air thermometer, which contains also a 

 coil of platinum wire connected in series with a 

 carbon resistance and a storage battery. The coil 

 is heated by means of the current from the battery, 

 and its temperature is adjusted by varying the re- 

 sistance, till the galvanometer shows that the 1 wo 

 thermo-j unctions are at the same temperature, 

 which is read off on the air thermometer. Some of 

 the advantages are that no assumption is made 

 about variation of thermo-effect with temperature 

 or about variation of voltage with temperature. r 

 with regard to temperature or temperature-co- 

 efficient of wires. The apparatus is extremely 

 simple. Parent y and Bricard (Paris Academy of 

 Sciences, April 27) have devised a self-registering 

 thermometer balance, in which the two arms carry 

 respectively a barometer and an air thermometer, 

 both dipping into the same mercury trough. At 

 constant temperature and varying atmospheric 

 pressure the equilibrium is undisturbed, the altera- 

 tions in the weight of the arms caused by move- 

 ment or' the mercury being the same for each, but 

 with change of temperature the equilibrium is de- 

 stroyed, and the beam moves. The apparatus can 

 be used also as a thermostat, llarker (London 

 Royal Society, June 18) has determined the freez- 

 ing point of mercurial thermometers by a new meth- 

 od, in which distilled water is cooled below the 

 freezing point, the thermometer is inserted, and 

 then freezing is brought on by dropping in a crys- 

 tal of ice. It was found easy to keep the tempera- 

 ture in the freezing vessel constant to one or 

 two ten thousandths of a degree for an hour at a 

 time. 



Temperature. Waggoner (Berlin Physical So- 

 ciety, Nov. 15, 1895) has measured the temperature 

 of a Bunsen flame with carefully tested thermo- 

 electric elements. He finds that the results are in- 

 fluenced by the thickness of the wires that he uses, 

 the thinnest wire giving the highest values in the 

 outer edge of the flame and in the zone of active 

 combustion, but not in the inner cone. By calcu- 

 lating from the highest results given by four wires 

 of different thicknesses, the value 1,750" C. was ob- 

 tained for a wire of zero thickness, and this was 

 taken as the temperature sought. 



Specific Heat. Lindau (Berlin Physical Society, 

 March 13) holds that the specific heat of gases may 

 be determined from their cooling during adiabatic 

 expansion. In opposition to this view, Planck 

 (ibid.) points out that the cooling does not depend 

 solely on specific heat, but also on the extent to 

 which the gas differs from a perfect gas. Amagat 



(Paris Academy of Sciences, Jan. 13) shows that 

 Joly's determinations of specific heats at constant 

 volume, and those at constant pressure by Lussana, 

 give widely different results when used as bases for 

 computing the ratio of the specific heats of air at 

 50 under pressures of 1 to 50 atmospheres. He 

 shows that Joly's figures are the more probable. 



Fusion. Demerliac (Paris Academy of Sciences, 

 May 18) has studied experimentally the lowering of 

 the melting point of benzene by pressure. The al- 

 teration in melting point for an additional pressure 

 of one atmosphere was found to be 0'0294, which 

 agrees, within errors of observation, with the al- 

 teration that can be deduced from the formula of 

 Clapeyron. Ramsay and Eumorfopoulos (London 

 Physical Society, Feb. 14) have measured the melt- 

 ing points of various substances by means of Joly's 

 meldometer, an instrument that consists essentially 

 of a strip of platinum heated electrically. Small 

 fragments of the substance are placed on the strip 

 and the temperature at which they melt is deduced 

 from the length of the strip. For calibration, gold 

 was used, and Violle's value of 1,045 C. for its fus- 

 ing point was taken. The zero point of the instru- 

 ment was found to be constant to within a quarter 

 of a degree. 



Conductivity. Peirce and Wilson (" American 

 Journal of Science," January) find that the tempera- 

 ture variation of the thermal conductivity of marble 

 and slate is practically null, these substances con- 

 ducting heat equally well at temperatures from 350 

 C. to zero. This result was reached by slicing slabs 

 into layers between every pair of which thermom- 

 eters were introduced. Villari (Paris Academy 

 of Sciences, Oct. 19) finds that gases that are sub- 

 jected to the action of a series of electric sparks 

 acquire increased conductivity for heat. Von Be- 

 zold (Berlin Physical Society, Nov. 22, 1895) explains 

 the so-called "thermic after effect" in thermal ex- 

 pansion by the assumption of minute nonconduct- 

 ing particles scattered through the conducting sub- 

 stance. 



Thermodynamics. Onnes (Amsterdam Royal 

 Academy of Sciences, Jan. 25), starting from the 

 theorem that Van der Waals's "corresponding 

 states" are dynamically similar, infers that the 

 cooling of the gas in Thomson and Joule's porous 

 plug will become zero and turn into heating, with 

 all gases, at sufficiently high temperatures. 



Light. Photometry. Whitman ("Physical Re- 

 view," January-February) has devised a new form of 

 photometer for colored lights, based on the " flicker " 

 principle discovered by Prof. Rood. The observer's 

 eye receives light alternately from a colored surface 

 and a rotating white disk that hides the surface 

 during half of each revolution. At high speeds the 

 flickering sensation that is noticed at first disap- 

 pears, and with it practically the sensation of color, 

 so that the instrument can then be used as an ordi- 

 nary photometer and different-colored luminosities 

 can be compared. Violle (Paris Academy of Sci- 

 ences, Jan. 13) finds that a flat flame of acetylene 

 burning under a pressure of 30 centimetres of water, 

 and used with a screen, gives perfectly satisfactory 

 results as a secondary photometric standard. 



Absorption. Spring (" Bulletin of the Belgian 

 Royal Academy "), in experiments on the trans- 

 parency of liquids, finds that the absorbent powers 

 of different liquids for light form a decreasing 

 scale, the simplest substance, water, offering the 

 greatest resistance. The influence of temperature 

 is considerable ; with a mass of liquid 26 metres 

 thick, a difference of temperature of half a degree 

 centigrade will produce opacity by means of the 

 currents to which it gives rise. 



Spectroscopy . Donath (Wiedemann's " Annalen," 

 August) has investigated bolometrically the absorp- 



