in a Magnetic Field at Different Temperatures. 



GS 



apart by means of two adjustable brass pieces cast so as to 

 tit over the pole-pieces and held by means o£ nuts and bolts 

 at the desired distance. This bath was connected to a boiler 

 and condenser, and so could be filled with vapour o£ liquids 

 boiling at suitable temperatures. The results given were 

 obtained when the bath was empty and when filled with the 

 vapour of act- tone or steam. 



The use of this steam-jacket surrounding the coil com- 

 pelled a gap between the pole-pieces nearly a centimetre in 

 width, so that the fields obtainable never reached 14,000 

 C.G.s. units. Experiments were also made at the tempera- 

 ture of liquid air, for which purpose a vacuum vessel 

 was made by Baumbach by flattening the lower portion 

 of a glass cylinder 2 inches in diameter until the opposite 

 faces were about 4 mm. apart, and surrounding this with a 

 jacket of similar shape. 



The experimental coil was then enclosed in mica and 

 immersed in liquid air contained in the vessel. The use of 

 this vessel required a gap between the pole-pieces of about 

 1'8 cms., so that experiments at this temperature were made 

 with fields which did not exceed 4000 c.G.s. units. The 

 metals used were supplied by Messrs. W. G. Pye & Co., while 

 for the Graphite I am indebted to the Morgan Crucible Co. 



Experiments with Cadmium. 



Experiments were made with currents through the electro- 

 magnet varying from 1*8 to 10 amperes. These currents 

 were measured by means of a Kelvin Standard Ammeter. 



The following table shows a few readings from which the 

 results given are obtained. 



December 13th, 1908. Bath heated by acetone. 

 t = 55°'3. Y = 210. X = 1520. r = 18*5 ohms. 



Current, through 



Deflexion on 



Deflexion due 



Electromagnet. 



reversal. 



to field. 







19 





i 4-4 . 



I 



123 







29 





44 



45 



22-7 







255 





4-4 



3 



20 7 







22 



22 1= mean. 



As previously explained an approximate balance was found 

 by making Y=210 and then adjusting X to 1520 ohms. 



