680 SCIENTIFIC RECORD FOR 1868. 



the relation/ (1)pi)=Q in gases, and on the law of expansion of gases 

 at constant volume. (Ann. Chim. Phys., April, 1883, V, xxvm, 456, 

 464, 480, 500.) 



Vernon Harcourt has devised an instrument for giving by simple in- 

 spection the volume of a mass of air which, saturated with humidity, is 

 capable of occupying unit volume under normal conditions. By divid- 

 ing the volume of a gas by the indications of the instrument it is re- 

 duced to the normal standard. The author has given to the apparatus 

 the name of aerorthometer. (Proc. Boy. Soc, xxxiv, 166 ; J. Phys., 

 August, 1883, II, ii, 374.) 



Waitz has studied the law of the diffusion of gases by means of opti- 

 cal methods of great delicacy. Carbon dioxide and air were used in the 

 experiments, the progress of the diffusion being shown by a continuous 

 displacement of the interference fringes. From this displacement 

 the composition of the mixture could be deduced at each instant, and 

 hence the coefficient of diffusion. The author concludes (1) that this 

 coefficient at the same depth depends upon the partial pressure of the 

 carbon dioxide, and (2) that it may be considered a linear function of 

 the depth ; consequently the theory of Maxwell cannot be exact, since 

 it leads to a constant value of this coefficient. The same is true of 

 Stephan's formula. Meyer's formula, in which this coefficient decreases 

 indefinitely with the partial pressure of the carbon dioxide, is also inex- 

 act. ( Wied. Ann., xvn, 201 ; J. Phys., April, 1883, II, n, 190.) 



Mascart has completed the details of construction of his gravity 

 barometer. It now consists of a modified siphon barometer, the lower 

 reservoir being closed, and containing nitrogen under a pressure which 

 sustains a column of mercury a meter high in the tube. To make an 

 observation the barometer is placed in a tin cylinder filled with water 

 and the temperature carefully noted. The upper end of the tube pro- 

 jects above ttiie liquid and the level of the mercury is then read off. 

 Experiments have been made with the new instrument at Hamburg, 

 Stockholm, Drontheim, and Tromso, as well as at Paris. (Jour. Phys., 

 August, 1883, II, ii, 341.) 



Dufour and Amstein have described a new registering barometer in- 

 stalled in the Meteorological Observatory of Lausanne. It consists of 

 a glass tube 6 mm. in interior diameter, bent four times at right angles in 

 the same plane, twice at each end, so that the ends project vertically. 

 This tube is suspended by its middle point. As the pressure varies, the 

 center of gravity also varies, and the tube rotates about the point of 

 suspension. A style attached to the lower part of the tube is thus dis- 

 placed horizontally and records its motions upon a strip of moving 

 paper. It has performed satisfactorily for two years. (Jour. Phys., 

 August, 1883, II, ii, 375.) 



Teissier has suggested the use of the air-pump for filling vessels 

 terminating in capillary tubes, such as specific-gravity flasks, thermome- 





