232 Intelligence and Miscellaneous Articles, 



that the inductions transmitted to C D and C D' are equal ; it is 

 sufficient therefore to measure the thicknesses of the dielectric 

 plates to determine by an easy calculation the ratio of the dielectric 

 constants of glass and sulphur. By means of experimental pre- 

 cautions which I cannot mention here I have been able to render 

 this method sensitive and exact. 



The glass plate which I employed was exactly 3 centim. thick. 

 For the other side, I cast two plates of sulphur in the form of 

 prisms of the same angle, in such a manner that by clipping them 

 together, as in Babinet's compensator, a plate with parallel faces 

 was formed the thickness of which could be varied. I found 3' 15 

 centim. for the thickness of the plate of sulphur which exactly 

 compensated the plate of glass. To complete the determination of 

 the dielectric constant of glass that of sulphur had to be obtained ; 

 this was easy, since sulphur is a nearly perfect dielectric. I 

 employed the method indicated by M. J. Curie* and found the 

 number 2-94= (1-67) 2 . 



This result is almost identical with that of Prof. J. J. Thomson. 

 Maxwell's law is not exactly verified, as the mean index of my 

 plate of glass is about 1*51, but the difference is much less than 

 that given by the values of dielectric constants obtained by the aid 

 of slower methods. My conclusion is the same as that of Prof. 

 J. J. Thomson. — Comjptes Bendus, May 11, 1891, p. 1058. 



ON AN IMPROVED METHOD OF DETERMINING SPECIFIC HEAT BY 

 MEANS OF THE ELECTRICAL CURRENT. BY PROF. PFAUNDLER, 



The method published in 1869, which depends on Joule's law 

 according to which the same current develops in spirals of wire 

 arranged in series quantities of heat which are proportional to the 

 resistances, has hitherto met with but few applications, owing to 

 the fact that it is only applicable to nonconducting liquids. The 

 author has got rid of this objection by replacing the spirals of wire 

 by thin glass spirals filled with mercury. He obtained also greater 

 accuracy and certainty by interposing these resistances as branches 

 in a Wheatstone's bridge, so that it was possible to control the ratio 

 of the resistances during the passage of the current and keep it 

 constant. Slight alterations of the resistances were compensated 

 by placing glass threads in the straight ends of the tubes which 

 contained the mercury. In other cases those alterations were 

 measured by displacing the contact-key, and in this way the result 

 was corrected. 



The comparative measurement of the rise of temperature is 

 made more sensitive by the aid of a thermopile. 



Experiments are communicated which show the applicability of 

 the method both for direct and alternating currents. — Wiener 

 Berichte, April 9, 1891. 



* Ann. de Chim. et de Phys. 1889. 



