l92 Miss EL Brooks on the Damping of the 



at the time t is further directly proportional to the surface of 

 contact of the reacting parts at the time r x + the instability 

 constant K. At a constant surface of contact of the reacting 

 parts of the heterogeneous system we have 2-f K= constant, 

 i. e. the instability constant does not become evident from the 

 form of the equation. 

 Davy-Faraday Laboratory 

 of the Royal Institution. 



IV. Damping of the Oscillations in the Discharge of a 

 Ley den-jar. By H. Brooks, B.A., Tutor in Mathematics, 

 Royal Victoria College for Women, Montreal *. 



fT^HE method employed in the investigation of this subject 

 -L depends on the partial demagnetization of a magnetized 

 steel needle when placed inside a solenoid through which a 

 leyden-jar discharge is passed. 



The action of a rapidly alternating current on a magnetized 

 steel needle has been investigated by Prof. Rutherford (Trans. 

 Eoy. Soc, June 1896), who has shown that the method can 

 bft employed as a simple means of comparing the intensities 

 of high-frequency currents, and also as a means of determining 

 the damping. 



Erskine (Wied. Ann. vol. lxii. Oct. 1897) has employed 

 such magnetized steel needles for measurements of the resist- 

 ance of metals and electrolytes for rapidly alternating currents, 

 and also for the determination of specific inductive capacities. 



The object of this investigation was to examine in detail 

 the damping of the electrical oscillations in leyden-jar circuits 

 under varying conditions of spark-length, capacity, and 

 pressure. 



The appearance of an air-break in the circuit connecting 

 the outer and inner coatings of the jar when the discharge 

 was passing, was examined by Feddersen by means of a 

 rotating mirror in which the spark was reflected. He found 

 that the image consisted of a series of bright and dark bands 

 rapidly decreasing in breadth and intensity; and when a large 

 resistance was placed in the circuit the image became a broad 

 band of light gradually fading away in intensity. 



This method was used by Trowbridge (Phil. Mag. vol. xxx. 

 1890, and vol. xliii. 1897), who photographed the image of 

 the electric spark drawn out by the rotating mirror and 

 measured the distances between the successive oscillations 

 shown by the dark bands on the photograph. In this way he 

 was enabled to make a comparison of the damping in a few 

 * Communicated by Prof. E. Rutherford. 



