156 Scientific Intelligence. 



hollow iron vessel is provided with another vessel closely fitting 

 it. The latter constitutes a Prony friction brake. It is properly 

 mounted with a scale pan at the end of a lever. The revolving 

 vessel is filled with mercury and the friction of the inner iron 

 vessel, of the Prony brake against the revolving vessel raises the 

 temperature of the mercury. The temperature of the mercury is 

 raised to 30° higher than that of the room, and the rotation of 

 the apparatus is so regulated as to maintain this heat constant. 

 Thus the generation of heat is equal to the radiation into the 

 room ; a simple calculation gives as a value of the mechanical 

 equivalent, J = 426, 262 mkg. with a mean error of each deter- 

 mination of ± 2*479. The apparatus is well calculated by its 

 simplicity to take the place of the old form of demonstration 

 apparatus. — Ann. der Physik, Nov. 12, 1890, pp. 748-755. 



J. T. 



10. Electrical waves in open circuit. — A. Elsas employes one 

 Daniell cell, and hangs a telephone upon a continuation of a wire 

 connected with one of the poles of this cell. The connection be- 

 tween the poles of the battery is broken close to these poles by a 

 peculiar current breaker. The telephone at the end of the wire 

 gives a tone which depends upon the self induction and capacity 

 of the wire upon which it is hung. Various modifications of this 

 experiment are described. The telephone is employed in place 

 of a Hertz resonator, to show waves on the wire of the open cir- 

 cuit. — Ann. der Physik, Nov. 12, 1890, pp. 833-849. J. t. 



11. Electrical Waves. — H. Ernst Lecher describes a new 

 method of studying Hertz's phenomena. Instead of a resonator 

 of the type employed by the latter, a Geissler tube is used. 

 Two parallel wires of known self-induction terminate at one end 

 in condenser plates, which are charged in an oscillatory manner 

 by a large Ruhmkorf coil excited by storage cells, TIpon the 

 other ends of the parallel wires rests the Geissler tube. A short 

 wire is then slid alo»g the parallel wires connecting them across 

 like a bridge between two parallel wires on a sonometer. At 

 certain definite points the Geissler tube glows, and the wave 

 lengths of the electrical oscillations can thus be measured. 

 Lecher finds that the velocity of electricity in metallic wires is 

 that of the velocity of light. He points out a slight inaccuracy 

 in Hertz's work. — Ann. der Physik, Nov. 12, 1890, pp. 850-870. 



J. T. 



12. Electrical Gyroscope designed for rectification of the 

 mariners Compass. — A small electrical motor sets in action a 

 gyroscope ; advantage is taken of the invariability of the plane of 

 rotation at definite positions in latitude and longitude, to correct 

 for the deviation of the mariner's compass. The instrument is 

 provided with a small astronomical telescope for observations on 

 the stars. The apparatus is the invention of M. G. Trouve. — 

 Coniptes Pendus, p. 913, Dec. 15, 1890. J. t. 



13. On the periodicity of the Aurora ; by M. A. Veeder (com- 

 municated). — If the numbers of stations reporting auroras daily 



