720 Dr. J. S. G. Thomas on a Kidl-Deflexion 



Experimental Results and Discussion. 



The following particulars refer to anemometer-tube R 3 r 

 used in the present investigation : — 



Ratio arm 1000 ohms. 



Internal Diameter of Flow Tube. ... 2*039 cm. 



External Diameter of Flow Tube. ... 2*238 cm. 



Internal Diameter of Shielding Tube. 0*242 cm. 



External Diameter of Shielding Tube. 0*419 cm. 

 Mean Diameter of unprotected and 



protected wire. 0*101 mm. 



Temperature coefficient of wire 0'003588. 



Ro. of exposed wire (0 = 0*02 amp.) 0*2337 amp. 



Ro. of shielded wire (0=0*02 amp.) 0*2445 amp. 



The whole of the flow system, including the anemo- 

 meter-tube, was tested for leakage by closing the outlet and 

 establishing a pressure of 10 - 5 inches of water within the 

 tube. At this pressure the leak was ascertained to be 0*06 

 cubic feet per hour. As the pressure in the flow tube during 

 a series of calibrations never exceeded 0*1 inch of water, the 

 leakage in the system is obviously extremely small and 

 negligible. 



A series of determinations was made of the variation 

 occurring in the values of the resistances of the respective 

 wires, heated by various currents (1*5 to 0*9 amp.) with vari- 

 ations in their inclinations to the horizontal. No detectable 

 variation with inclination occurred in the resistance of the 

 shielded wire, for all values of the inclination from the 

 horizontal to the vertical position. Subsequent investigation 

 showed that any such variation as occurred was certainly 

 less than 02 per cent, of the initial resistance of the wire. 

 The enclosure shielding this wire appears, therefore, to 

 have been of such dimensions that no appreciable con- 

 vection current from the wire employed is set up therein 

 when the heating current employed has any value up 

 to 1*5 amp. The determination of the dimensions of a 

 chamber wherein the free convection effect experienced 

 by a fine heated wire is negligible is of importance in 

 connexion with the design of the katharometer * 3 and the 

 method of rotation of the chamber as described affords a 

 ready means of ascertaining the degree of elimination of such 

 free convection current in any given case. In the case of 

 the exposed wire, considerable alteration of resistance 



* Dayn.es, Proc. Koy. Soc. A. vol. xcvii. p. 276 (1920). 



