654 



Mr. J. 8. G. Tho 



mas o??, c/^ 



f/i, 



by the second wire in the former case is considerably less 

 than in the latter case, and corresponds moreover to a 

 considerably higher value o£ the impressed velocity. Fig. 3 

 shows analogous results to those given in fig. 2, employing 

 platinum wires of diameter 0*202 mm. The corresponding 

 deflexion-velocity curves are given in fig. 1, together with 

 the calibration curve for the same wires when mounted at 

 an inclination of 45° to the horizontal. The values given 

 in Table III. are deduced from the results represented in 

 figs. 2 and 3. 



Table III. 

























02 



u 



"5 £ 



O nd 

 o ^ 



03 q 





city o 

 whic! 

 istanc 

 seconc 

 sec). 







d 



^o 



o 



.2 S 



Ratio : 



r-H <D W S 



Diameter 



of 

 Wires 

 (mm.) 



Plane 

 Vv ires. 



OS 



pe rat nre c 

 ro flow (° 



stance of 

 re. Zer 

 hm.). 



imum res 

 tained by 

 re (ohm). 



Max. Res. 

 Initial Res. 



ressed ve 

 •earn at 

 aximum r 

 attained ' 

 ire (cm. p 







a o3 



w 



1* 



"Si te o 



3* S 





cu-u d m & 



0101 



Horizontal. 



1:2 



470 



0-642 



0686 



1-068 



5-2 





Vertical. 



1-2 



555 



0-698 



0710 



1-017 



1-8 



0-202 



Horizontal. 



3-3 



472 



0-1976 



0-212 



1073 



5-9 





Vertical. 



3-3 



538 



0-2121 



0-218 



1027 



2-0 



(2) Dependence of the critical velocity — £/*e velocity at which 

 the maximum galvanometer deflexion occurred — upon 

 (a) the heating current employed and (b) the diameter 

 of the wires. 



In order to determine how the critical velocity — i. e., the 

 velocity at which the galvanometer deflexion attained its 

 maximum velocity — depended upon the heating current 

 employed in the bridge, a number of calibration curves 

 of directional anemometer D4 (diameter of wires O'lOl mm.) 

 were obtained, employing heating currents in the bridge 

 ranging from 0*7 amp. to 1*5 amp., the temperature of the 

 wires being thereby raised to temperatures ranging from 

 125° C. to 842° C. The various calibration curves obtained 



