Etfect of slow ^Current of Air flowing past Platinum, 241 



Experimental. 



The flow-tube employed in the present series of experi- 

 ments had a diameter of: 2*0534 cm., the same as that used 

 in previous work referred to above. Fig. 1 illustrates the 



Fiff. 1. 



manner in which the heated platinum wires employed — 

 eleven in number — were mounted, and their mode of in- 

 sertion in the flow-tube. The respective ends of each of the 

 fine platinum wires W were affixed, by means of the smallest 

 amount of silver solder affording a secure junction, to por- 

 tions of considerably thicker copper wires represented by 

 L, L. These copper wires passed tightly through holes in 

 plugs of ebonite P, P, which fitted accurately into rect- 

 angular slots furnished by projections joined to the main 

 tube at right angles, as shown. Precautions were taken that 

 the slots were diametrically disposed with respect to the 

 cross-section of the flow-tube, and after insertion of the 

 plugs the continuity of the inner surface of the tube was 

 restored by carefully filing and polishing the inner surfaces 

 of the respective inserted ebonite plugs. The resistances 

 of the several platinum wires were made as nearly equal 

 as possible in the manner previously explained* ; and by 

 appropriate adjustment of the copper wires to which the 

 platinum wires were affixed, it was possible to secure that the 

 several wires were initially coplanar, and remained equally 

 spaced in the initial diametral plane of the flow-tube on being- 

 heated by means of an electric current. The copper wires 

 passing through the ebonite plugs were, after adjustment of 

 the platinum wires as above, secured in position by means 

 of small screws passing through fine brass bushes inserted 



* Phil. Mag. vol, xl.pp. 641, 642 (1920). 

 Phil. Mag. S. 6. Vol. 41. No. 242. Feb. 1 921. 11 



