1889.] Revision of the Atomic Weight of Gold. 



71 



Villari's strained disk and Liidtge's strained prism. The disk was 

 free from strain in the middle, the prism free from strain at the ends. 



I have repeated Villari's experiment at the Cavendish Laboratory, 

 using, at Mr. Glazebrook's suggestion, an elliptic analyser to deter- 

 mine the magnetic rotation. With the disk spinning about 200 times 

 a second, the magnetic rotation was reduced from 10° to 6°. This is 

 not so great a diminution as Yillari observed, bat his glass may have 

 been softer and more easily strained. 



Yillari thought that the effect he observed was due to the time 

 required to magnetise the glass. That this supposition was erroneous 

 has been clearly established by the experiments of Bichat and 

 Blondlot, recently repeated by Dr. Lodge. In these experiments 

 the oscillating discharge of a Leyden jar was found to rotate the plane 

 of polarisation in time with the oscillations. Before hearing of these 

 results I had myself attacked the problem in a somewhat similar 

 manner. A coil of wire was wound round a piece of heavy glass, and 

 a current alternated 250 times a second by a tuning-fork was sent 

 through the coil. The current was measured by a dynamometer and 

 a tangent galvanometer. The first gave the measure of the current 

 independently of its sign, the second showed that the integral current 

 was zero. When the current was passing it was found impossible to 

 extinguish the light, owing to the rapid alternations of the plane of 

 polarisation. 



In conclusion, I have to express my thanks to Professor Thomson 

 and Mr. Grlazebrook for many kind suggestions and encouragement, 

 and especially to Professor Thomson for the privilege of using the 

 Cavendish Laboratory. 



II. " Revision of the Atomic Weight of Gold," By J. W. 

 Mallet, F.R.S., Professor of Chemistry in the University 

 of Virginia. Received April 15, 1889. 



(Abstract.) 



After noticing and giving the results of the earlier determinations 

 of the atomic weight of gold, and the recent researches of Kriiss and 

 of Thorpe and Laurie, the author reports upon experiments of his 

 own in the same direction, which have occupied much of his time and 

 labour for the last three or four years. 



The difficulties connected with the accurate determination of the 

 atomic weight of this metal are remarked upon, and the general 

 principles are reviewed which ought to be observed in all investiga- 

 tions of this kind. 



The means and methods of weighing used are stated, and the pre- 



