foote: macnktic rotation I 15 



TABLE II 



Volts (max.) 47(H) 7100 11 inn L4500 18600 



Decrement 0.0435 0.0440 0445 0445 0445 



Comparisons were next made between throe jars in oil and three 

 in air using the added resistance method in a circuit excited by a 

 quenched gap circuit. The results were found to vary according 

 to the cleanliness and nature of the glass in the jars exposed to t he 

 air; the difference in resistance in air and in oil being nearly negli- 

 gible at 4000 volts, and amounting in the Wireless Specialty jars 

 to about 1.4 ohms at 20000 volts. The increase was approxi- 

 mately proportional to the square of the voltage, in agreement 

 with the results of Fleming. 



From this follows a conclusion which is contrary to the ordi- 

 narily accepted view; that is, that the brushing losses are not 

 reduced by placing jars in series if the capacity and voltage remain 

 the same, for if one jar be replaced by four jars in parallel series, 

 the voltage on each jar is reduced to one-half and the loss per jar 

 to one-fourth. The brushing surface is increased four times there- 

 fore the total loss remains the same. This conclusion was proved 

 by experiment to be correct. 



Another experimental fact which is not so easily explained is thai 

 the losses in jars with only their edges immersed in oil are consid- 

 erably greater than when the whole conducting surface is covered. 

 This result is opposed to the idea that the air losses lie wholly at 

 the edges of the conducting coatings. This fact has been verified 

 a number of times. 



PHYSICS.— The magnetic rotation and ellipticity for massive 

 metal mirrors. Paul D. Foote. Communicated by ( J. W. 

 Waidner. To appear in the Physical Review. 



Plane polarized light incident normally upon a mirror of a 

 magnetic substance placed in a magnetic field in which the lines 

 of force are perpendicular to the mirror surface, is, in general. 

 reflected in the form of an elliptic vibration whose axes are inclined 

 at a small angle to the plane of the incident polarization. A series 

 of measurements were made upon mirrors of iron, cobalt, steel, 



