690 



Dr. J. S. Q. Thomas on 



Experimental. 



The flow tube consisted o£ a brass tube of 2'011 cm. 

 diameter wound with one layer of asbestos cord (diameter 

 of cord about 3 mm.), inserted in the flow system as detailed in 

 previous papers *. The sups ly of air was derived from a gas- 

 holder of 5 cubic feet capacity connected with the laboratory 

 hi.uh-pressure air service, and a steady and calculable flow 

 of dry air in the system was established as already detailed t« 

 The heating element employed is shown in fig. 1 [a and b). 

 A is a portion of brass tube (i mm. in length, exactly simi'ar 

 to the main flow tube. It fitted tightly within the ebonite 

 ring B. A number oE thin copper pins, bent at right angles 



B- 



A 



l*C 



IA\ l^ 



6. 



as shown at C in fig. 1 b, were driven securely into holes 

 drilled in the ebonite ring, and slots were cut of an appro- 

 priate width and depth in the brass ring A so that these pins 

 were insulated from the latter. A length of fine platinum 

 wire was soldered in zigzag fashion to these pins as shown, 

 the minimum amount of solder being employed for this pur- 

 pose. The ends of the wire were connected by short copper 

 leads with the terminals T. Holes H were drilled at angular 



* See e.g. Phil. Mag. vol. xli. p. 242 (1921). 

 t Phil. Mag. vol. xxxix. p. 509 (1920). 



