PHYSICS, PROGRESS OF, IN 1894. 



053 



tained to the thousandth of an inch of mercury 

 without a vernier. 



Heat. Tliermometry. Barille (Paris Acad- 

 emy of Science, Jan. 29) has devised an electric- 

 alarm thermometer for laboratory ovens. When 

 the mercury reaches the desired point a circuit 

 is closed by a platinum wire attached to a small 

 iron tube that slides along a fixed wire and that 

 is regulated in position by a magnet attached to 

 the supporting frame. Baly and Chorley (" Na- 

 ture," April 5) have devised a high-temperature 

 thermometer in which the expanding substance 

 is a liquid alloy of potassium and sodium. This 

 alloy boils at about 700 0. and solidifies at 

 8 C., and the thermometer should be par- 

 ticularly useful for determining high boiling 

 points. 



Specific Heat. Silvio Lussana ("Ntievo Ci- 

 mento," abstracted in " Nature," Sept. 20) has 

 obtained the specific heats of gas by an ingen- 

 ious apparatus that uses the same gas over and 

 over again, and thus obviates the necessity of a 

 large amount of gas. 



Expansion. Max Toepler ( Wiedemann's " An- 

 nalen," October) finds that the coefficient of ex- 

 pansion of elements in the solid state and their 

 change of volume during melting show a definite 

 relation. 



Conductivity. I. T. Osmond (" Physical Re- 

 view," November-December) finds that the ther- 

 mal conductivity of cast iron is about 15 per 

 cent, greater from a little below 100 C. to 200 3 

 than it is between 60 D and 90. Saret (" Biblio- 

 theque Universelle," No. 4, 1893), from examin- 

 ing the shape of the isotherms in certain sections 

 "of crystals of gypsum, finds no evidence of the 

 existence of rotational coefficients of conduc- 

 tivity. 



High Temperature. C. Barus (" American 

 Journal of Science," October) points out various 

 anomalies in the accepted results of researches 

 on high temperatures, and states that to clear 

 these away either the boiling point of zinc must 

 come down from 930 to 905 C., or else the 

 melting points of gold, silver, and copper must 

 move up 30 or 40, or both must move toward 

 each other by corresponding amounts. 



Sound. Velocity. J. W. Lowe (Wiede- 

 mann's " Annalen," August) finds, from experi- 

 ments with a Quincke interference tube, that 

 contrary to the results of Kundt, Regnault, 

 Konig, and others for closed tubes the velocity 

 of sound in air and in carbolic acid is the same 

 for notes of different pitch and intensity when 

 they are propagated in open space. 



Pitch. P. Melcle (Wiedemann's " Annalen," 

 June) has devised a new method of determining 

 the pitches of high tuning forks independently 

 of the ear. The fork is vibrated with one prong 

 touching a metallic rod clamped at one end, 

 which is thus caused to vibrate transversely, and 

 the pitch is determined from the nodes of this 

 rod, observed by means of fine sand that has 

 been dusted on it. 



Beats. It is well known that two timing 

 forks produce beats even when one is held to 

 each ear in such manner that a sound wave can 

 not pass from one to the other through the air. 

 Wundt thought that in this case the beats had 

 their origin in the brain. Schaefer, however 

 (" Zeitschrift fiir Psychologic und Physiologic 



der Si nnesorgane"), regards the effect as due to 

 conduction by the bones of the skull. 



Residual Sensation. Alfred M. Mayer ("Amer- 

 ican Journal of Science," January) has investi- 

 gated the connection of the pitch of sounds with 

 the length of their residual sensations that is, 

 with the sound perceived by the ear after actual 

 vibration has ceased. The duration of the resid- 

 ual sound was measured by rotating perforated 

 disks opposite the nipples of resonators that 

 were sounded by tuning forks and noticing at 

 what speed of rotation the interrupted sound 

 seemed to become continuous. The duration 

 was less the higher the pitch, varying from 

 0-0231 second for a frequency of 128 to 0'0049 

 second for a frequency of 1,024. 



Minimum of Audibility. Lord Rayleigh 

 (" Philosophical Magazine," September), in ex- 

 periments to determine the minimum current 

 audible in the telephone, finds that the maxi- 

 mum sensitiveness to currents occurs in the 

 region of frequency 640, where a current of 

 4-4 X 10~ 8 amperes produced an audible sound. 

 Telephones varied greatly in sensitiveness. The 

 same writer (ibid., October), in experiments on 

 the amplitude of just audible aerial waves, finds 

 that for a frequency of 256 this amplitude is 

 about 1-27 X 10~ 7 centimetres. 



Light. Luminosity. P. Glan (Wiedemann's 

 " Annalen," March) finds that the ratio of the 

 volume of a candle flame to its illuminating 

 power is very nearly constant, the difference be- 

 tween the actual luminosity and that calculated 

 from this ratio being never greater than 3 per 

 cent. Equal volumes of the bright flame of 

 any two candles thus give the same amount of 

 light. 



Reflection. W. Wernicke (Wiedemann's " An- 

 rialen," March) shows that when light is reflected 

 from a silver film between two transparent me- 

 dia, the anterior of which has the higher refrac- 

 tive index, there is not only a normal accelera- 

 tion of phase increasing continuously from zero 

 to \ or f of a wave length as the thickness of the 

 silver increases from zero to opacity, but also an 

 anomalous retardation, which shows itself when 

 there are traces of another substance between 

 the silver and the front medium, and which 

 may amount to between and f of a wave 

 length. 



Absorption. G. B. Rizzo (Turin Academy) 

 finds that Kirchhoff's law connecting the ab- 

 sorptive and emissive powers of substances does 

 not. hold good for cobalt glass. While its emis- 

 sive power decreases nearly uniformly between 

 wave lengths 685 and 580, the absorptive power 

 shows decided maxima in the red, yellow, and 

 green, that have no relation whatever to the 

 emission. 



Dispersion. II. Rubens (Wiedemann's "An- 

 nalen," October) finds that Helmholtz's electro- 

 magnetic theory of dispersion accords with re- 

 sults obtained for fluorspar, quartz, rock salt, 

 sylvine, and one of the heavy Jena silicate 

 flint glasses over the region of the spectrum 

 that was investigated 5 octaves. 



Photometry. J. B. Spurge (London Physical 

 Society, Jan. 26) employs a photometric method 

 in which two diffusing screens, illuminated re- 

 spectively by the lights to be compared, are used 

 as secondary sources, and the luminosities of the 



