Intelligence and Miscellaneous Articles. 527 



transport more than one part of the quantities furnished by con- 

 duction ; a portion remaining in the transitional stage between 

 dielectric displacement and heat, in the form of a sort of packing 

 in the substance of the dielectric. The quantities of electricity- 

 stored up in this way in the course of time form the residue. The 

 true resistance of the substance can only be obtained after its com- 

 plete development. The current which traverses the imperfect 

 dielectric has thus acquired a constant intensity, for the quantity of 

 electricity arriving each moment is usually equal to that converted 

 into heat, and is not partially used in the formation of a residue. 



The investigation extended to the following substances : — 

 Petroleum ether, oils of turpentine, of linseed, castor oil, olive 

 oil, almond oil, bisulphide of carbon, oil of vaseline, benzole, 

 toluole, xylole, water, alcohol, ether, and the solid insulators in 

 ordinary use. 



Of liquids the best insulators are the products of distillation of 

 petroleum, although individual specimens dilfer very materially 

 from each other. 



The specific resistance of petroleum, ether, vaseline oil, and 

 benzole was in most cases higher than 10^* Siemens units. — BericJite 

 der Akad. zu Wien, Feb. 1889. 



THE ISOTHERMS OF GASES. BY M. AEOLDO VIOLI. 



The author deduces from the kinetic theory the general relation 

 between pressure, volume, and temperature of a gas. The begin- 

 ning of the investigation is occupied by an historical account of the 

 efforts hitherto made in this direction which have led to various 

 formulae. On the basis of various hypotheses as to the mode of 

 action of the molecules, and of the surrounding atmospheres, the 

 following equation is finally established : — 



H+_^ - U(1-6) = R. 



^2{i;(l-6)(l + aOr i 

 In this H is the pressure in metres of mercury, t the temperature 

 in degrees Centigrade, a the coefficient of expansion of perfect 

 gases, V the volume reduced to (/% a the constant of molecular 

 attraction, h the ratio of the volume of tlie molecules to the volume 

 of the gas, and R is a constant. Separate expressions are pro- 

 pounded for the magnitudes a and h : namely 



3/- 1 



a = 0-000004568jp^^9j7i - i^^^Qli 

 6=0-0005 V_p; 



in which p is the molecular weight for H.^=2, h the pressure in 

 metres of mercury, and n the number of atoms in a molecule. 



These formula? have been applied to gases in various directions, 

 and the results compared with the theories of Van der Waals and 

 of Blaserna. The conclusion consists of investigations on mole- 

 cular velocity as well as on the critical point. — Bend, dellali. Ace. dei 

 Lincei, vol. iv. pp. 285 et seqq. ; BeihUitter der Physilc, vol. xiii. p. 66. 



