DIELECTRIC CAPACITY OF LIQUIDS AND GASES. 483 



isotropic or crystallized bodies, by varying the duration of the discharge 

 between pretty wide limits. Bad insulators soon show themselves 

 as conductors ; even for very short contacts it is difficult to prove 

 that specific inductive capacities are unequal in various directions. 



1073. LIQUIDS. The determination of the specific inductive 

 capacity of liquids presents special difficulties, owing to the fact that 

 the molecules of the liquid carry electricity from one armature to 

 the other. We know that it is impossible to give a somewhat strong 

 charge to a liquid dielectric, and particularly to keep it charged. 



With this reserve, we may employ the methods described above. 

 Professor Silow* used a modification of the quadrant electrometer. 

 The quadrants are replaced by four cylindrical sectors, consisting of 

 tinfoil fixed on the inside of a glass cylinder, and the needle of two 

 cylindrical sectors concentric with the first. The needle is in con- 

 nection with the earth, and the two systems of opposed quadrants 

 with the poles of an insulated battery, the centre of which is to earth. 

 The deflection is measured when the apparatus is full of liquid oil 

 of turpentine, for instance. F<?r the same difference of potential, 

 the deflection is proportional to the capacity, and this, again, to the 

 specific inductive capacity ; by reversing the connections of the poles 

 with the quadrants, and measuring the double deflection, a zero 

 reading is avoided. 



1074. GASES. The objection relative to the transport of elec- 

 tricity by molecules does not seem to have the same importance 

 for gases, as experiment shows that the charge of a gas condenser 

 can be maintained for a long time. Faraday, f notwithstanding 

 numerous attempts, was unable to show any difference in the specific 

 inductive capacity of various gases ; these differences are too small 

 to be shown by the methods which he employed. Boltzmann,J and 

 afterwards Professors Ayrton and Perry, succeeded in the following 

 manner. 



Boltzmann's condenser consists of two parallel metal plates, A 

 and B, placed under a bell jar, and protected* by larger plates against 

 any external influence. The plate A is permanently connected to the 

 positive pole of a battery of 300 elements, the other pole of which 

 is to earth, and to one pair of quadrants of an electrometer, the 



* SILOW. Pogg.'Ann., Vol. CLVI., p. 389. 1875. 



f FARADAY. Exper. Researches, 1290, Vol. I., p. 407. 1837. 



\ BOLTZMANN. Wiener Sitz. Berichte, Vol. LXIX., p. 795. 1874. 



AYRTON and PERRY. Mem. lu ^ la Soc. As. du Japan. Yokohama, 1877. 



I I 2 



