518 Intelligence and Miscellaneous Articles. 



propagation through air is very sensibly equal to that which this 

 same circle gives along wires, the quarter of each being itself 

 almost equal to twice the diameter of the corresponding circle. 

 From this it follows that the velocity of propagation of Hertz's elec- 

 trical oscillations across air is very nearly the same as that with 

 which they are transmitted along a conducting wire*. — Comptes 

 Rendus, March 31, 1891. 



ON AX IMPROVED METHOD OF DETERMINING SPECIFIC HEATS 

 BY THE ELECTRICAL CURRENT. BY PROF. J. PFAUNDLER. 



The method published by the author in 1869, which depends on 

 Joule's law, in which one and the same current develops quantities 

 of heat, in coils of wire arranged in series, which are proportional 

 to the resistances, has hitherto found but few applications from the 

 circumstance that it only applies to non-conducting liquids. The 

 author has got rid of this drawback by substituting for the coils 

 of wire spiral glass tubes filled with mercury. He has also given 

 the method far greater accuracy and certainty by inserting three 

 mercury resistances in the branches of a Wheatstone bridge, by 

 which it is possible to control and keep constant the ratio of the 

 resistances during the passage of the heating-current. Small 

 variations in resistance are compensated by introducing glass 

 threads in the straight ends of the tubes which contained the 

 mercury. In other cases these changes are measured by displacing 

 the contact-key, and in this way the result is corrected. 



The comparative measurement of the rise of temperature is 

 made more delicate by means of a thermopile. 



As instances of the utility of the method, experiments were made 

 both with continuous and with alternating currents. The attempts 

 of the author to use this method for the determination of the 

 thermal capacity of water at different temperatures were inter- 

 rupted by the author's transference to Griitz, and will be repeated 

 on a larger scale ; these experiments are to be regarded as pre- 

 liminary ones intended to test the method. — Wiener Berichte, 

 April 9, 1891. 



ON PERIODICALLY VARIABLE ELECTROMOTIVE FORCES WHICH 

 ACT ONLY IN ONE DIRECTION IN A CONDUCTOR WITH SELF- 

 INDUCTION. BY PROF. PULUJ OF PRAG. 



In this paper the laws of the flow of electricity in a conductor 

 with self-induction are theoretically investigated, when the external 



* We have already enunciated this in a preliminary communication 

 made on this subject to the Societe de Physique et d'Histoire naturelle 

 de Geneve at a meeting on May 1, 1890 (Archives des Sciences phys. et 

 nat. vol. xxiii. p. 557) ; we have since then completely repeated the 

 researches by varying the conditions in a number of ways, and it is 

 this latter research which we give here. M. Lecher, in Vienna, has 

 found by an entirely new method that the velocity of electrical undula- 

 tions along a wire is equal to that of light. 



