PHYSICS IN 1899. 



705 



abnormal, about 600 metres per second, or nearly 

 twice that of sound. On reflection at the ends 

 the waves are re-enforced in intensity, owing 

 probably to the fact that the gas in the tube 

 moves in the direction of propagation on the pas- 

 sage of the waves, which movement is arrested 

 by the ends of the tube. 



Pitch. Stumpf (Wiedemann's Annalen, Janu- 

 ary) defends the method of determining high 

 pitches by means of difference tones, which he 

 regards as convenient and reliable. When the 

 primary notes are in the same octave there are 

 only two difference tones below them, one repre- 

 senting the difference between the two notes 

 sounding together, and the other the difference 

 between the higher note and the octave of the 

 lower one. As the higher note ascends the pitch 

 of the first difference tone rises, while that of 

 the second one falls. Von Lang (Wiedemann's 

 Annalen, June) finds that stretched India-rubber 

 threads when vibrated give a constant note be- 

 tween certain lengths, because the ratio of length 

 to tension remains constant during the stretching. 



Beats. Maltezos (Paris Academy of Sciences, 

 Aug. 28) notes that the ordinary equation for a 

 thin elastic string, giving the relation between the 

 number of vibrations, tension, section, and length, 

 does not explain beats. Taking into account the 

 rigidity of the string, he deduces theoretically an 

 expression for the number of vibrations, which 

 leads to the conclusion that the number of beats 

 is proportional to the square root of the area of 

 the section, inversely proportional to the cube of 

 the length, and inversely proportional to the 

 square root of the tension. The last conclusion 

 agrees with experiment, but the second does not, 

 experiment showing that the number of beats is 

 nearly inversely as the simple length of the 

 string. Hence some additional factor beyond 

 rigidity must enter into the problem, probably a 

 difference of elasticity in two directions across the 

 sectional area. 



Radiophony. Dussaud (Comptes Rendus, 

 XXVIII, p. 171) has transmitted sound to a 

 distance of 10 miles by using a selenium cell in- 

 fluenced by ultraviolet light through the inter- 

 mediary of a fluorescent screen. Sella (Nuovo 

 'Cimento, VIII, p. 4) also uses ultraviolet light, 

 but substitutes an influence machine for the se- 

 lenium cell. The light, falling on a short air gap, 

 modifies the sound of a telephone in circuit. 



Heat. Expansion. Le Chatelier (Paris Acad- 

 emy of Sciences, Aug. 7) finds that, while differ- 

 ent specimens of iron and steel expand similarly 

 up to about 750, above the temperature of mo- 

 lecular transformation they expand very differ- 

 ently, according to the amount of carbon present. 

 For an increase of carbon from 0.05 to 1.2 per 

 eent., the coefficient doubles. 



Temperature. Berkenbusch (Wiedemann's An- 

 nalon, LXVII, 3, p. 649), using two new methods 

 for measuring flame temperature indicated by 

 Nernst one founded on an estimation of the rate 

 of heating and cooling of a thermo-couple, and 

 the other on the electrical heating of a thermo- 

 element to the temperature of the flame finds 

 that points in a Bunsen flame give a mean of 

 1,S30. This accords with Waggener's results and 

 with thermo-chemical calculation, which gives 

 1,820. 



Rddiation. Angstrom (Wiedemann's Annalen, 

 LXVIT, 3, p. 633) has devised what he calls an 

 electric compensation pyrheliometer for measur- 

 ing thermal radiation. Of two similar thin metal 

 strips, one is exposed to the radiation, while the 

 other is heated correspondingly by an electric 

 -current supplying a known quantity of energy. 

 VOL. xxxix. 45 A 



Crova (Annales de Chimie et Physique, No. 17) 

 calculates the intensity of solar radiation from 

 the readings of a thermometer whose spherical 

 black bulb is concentric with a metal sphere with 

 a small window in it. The instrument is kept 

 in partial shadow by diaphragms. Thus inclosed 

 and protected, when the interspace between bulb 

 and sphere is maintained at constant tempera- 

 ture the bulb shows by its rise of temperature 

 in a given time the amount of radiant energy in- 

 cident upon the exposed area. 



Conduction. Lees (Memoirs of the Manchester 

 Literary and Philosophical Society, XLIII, 8, p. 

 1) finds that the thermal conductivity of glass, 

 ebonite, and soft sandstone increases with pres- 

 sure, while that of granite and marble did not 

 change within the limits of the experiment (1 to 

 54^ atmospheres). The same experimenter (Philo- 

 sophical Transactions, CXCI, p. 399) finds that 

 poor solid conductors (except glass) generally de- 

 crease in conductivity with increase of tempera- 

 ture in the neighborhood of 40 C.; that liquids 

 follow the same law near 30 C.; that conductiv- 

 ity does not always change abruptly at the melt- 

 ing point; that the conductivity of a mixture 

 lies between the conductivities of its constitu- 

 ents; and that mixtures of liquids decrease in 

 conductivity with increase of temperature at 

 about the same rate as their constituents. Hempel 

 (Wiedemann's Annalen, January) finds that the 

 improved Dewar vacuum insulator (see article 

 on LIQUID Am, Annual Cyclopaedia, 1898) will 

 maintain the temperature of test tubes filled with 

 ether and solid carbonic acid as low as 70 for 

 eighty-eight minutes. Tubes packed in wool, 

 cotton, or silk rose to 45 to 55 in the 

 same time. Eiderdown kept the temperature 

 down to 66. 



Ebullition. Richards and Harrington (Zeit- 

 schrift fur physikalische Chemie, XXVII, p. 421) 

 have inquired whether the fact that a solution 

 of mixed salts boils at a lower temperature than 

 that calculated from adding the depressions cor- 

 responding to the constituents may not be due 

 partly to the fact that the dissociation of one 

 salt is affected by the presence of another. They 

 find that molecular combinations appear to ac- 

 company the reaction. 



Solidification. Battelli and Stefanini (Nuovo 

 Cimento, IX, p. 5) conclude that the molecular 

 depression of the freezing point remains practi- 

 cally constant as dilution increases, and that for 

 very dilute solutions it does not differ much 

 from 1.87. This agrees with the results of Raoult, 

 but not with those of the majority of other in- 

 vestigators. Tammann (Zeitschrift fur physika- 

 lische Chemie, XXVIII, p. 17), in a determination 

 of the viscosities of various supercooled organic 

 substances, finds that in the neighborhood of the 

 freezing point the viscosity increases normally, 

 but at an average of 90 below it the increase 

 begins to be abnormally rapid. The same investi- 

 gator (Wiedemann's Annalen, LXVII, 4, p. 

 871), after an inquiry regarding a critical state 

 between the solid and liquid states, concludes 

 that no such state has ever been observed. An 

 apparently continuous transition from the crys- 

 talline to the liquid state has been reported, but 

 only when the conditions are unfavorable for see- 

 ing the dividing surface. 



Specific Heat. Sohncke (Wiedemann's An- 

 nalen, LXVI, 1, p. Ill) concludes from the close 

 agreement of the temperature coefficient of the 

 specific heats of solids, liquids, and gases that for 

 all bodies (when not near a change of state) the 

 change of specific heat with temperature is deter- 

 mined chiefly by increase of internal molecular 



