366 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



about 0.25 mm. thick was obtained from Drew, a gold-beater in Boston. 

 It was stated by him to be very pure. Its density was determined by 

 weighing in and out of water at a known temperature, and was found by 

 this method to be 19.27 relatively to water at 4° C. From this gold 

 two crosses, called hereafter Plate 1 and Plate 2, were cut about 3 cm. 

 long and 1.1 cm. wide. Contact was made at both the primary and the 

 secondary electrodes by electroplating with copper. The gold was fas- 

 tened on a glass plate with a mixture of resin and beeswax. The plate 

 was placed in a tank through which a current of water was kept flowing. 

 A thermometer was kept in this tank, and the temperature noted. 



The currents, the resistances, and strengths of the magnetic fields were 

 measured as described above. The last mentioned measurement was 

 taken before and after each series of measurements of the Hall effect 

 with Plate 1. The strength of the magnetizing current was not read, 

 however, during the measurements of the transverse effect in the case 

 of this plate. 



The thickness of the plates was estimated by weighing, the value of the 

 density mentioned above being used, and was also measured with the 

 calipers. The effective thickness was taken as the thickness of the plates 

 between the secondary electrodes. The ratio of this thickness to the 

 average thickness was obtained, therefore, by means of the calipers, 

 while the average thickness was obtained by weighing. 



In the following tables, 



i is the transverse current in amperes, 



R is the resistance of the transverse circuit in ohms, 



e is the transverse electromotive force in volts, 



/is the main current in amperes, 



M is the strength of the field in c. g. s. units. 



The value of 



e d 



-^r-r-, is given in c. g. s. units. 

 131 ° 



April 23. Plate 1 ; thickness 0.0238 cm. 



