510 Mr. R. Hosking on the 



A set of readings was taken at 25 c C. and also at 0° C, 

 and values for K 25 and K were found. The results are 

 tabulated below, and the corresponding graphs appear in 

 fig. 6. Thev bear out the conclusions arrived at in connexion 

 with the results at 50° C. 





Tube I. 



Tube II. 



Tube III. 



Tube IV. 



K(25'0) 



•00896 

 •01791 



•003407 



•00893 

 •01790 



•002908 



•00892 

 •01790 

 •003774 



•00890 

 •01791 

 •003172 



T ^ 



E/L 



In the general reduction formula, the most difficult constaut 

 to measure accurately is R, the mean radius of efflux. Capil- 

 laries are not generally right circular cylinders, nor even ellip- 

 tical cylinders ; and as the degree of precision with which R 

 must be calculated is always four times as great as that required 

 in the deduced viscosity, the examination and measurements 

 of the capillaries must be carried on with extreme care. 



Tubes L, II V III., and IV. were in the first place selected from 

 a large number on account of their uniformity of bore — tested 

 with a small mercury column — and their circular end sections. 



The first method of measuring R was by contained volumes 

 of mercury. The values obtained (at 0° (J.) for the mean radii 

 were -018968, '018926, '020416, and '020482 cms. respectively. 



At the conclusion of all the experiments sections about 

 J cm. in thickness were cut from the tubes at regular in- 

 tervals ; they were ground, polished, and mounted in a brass 

 plate. Three independent sets of readings of their dimen- 

 sions were obtained by me — firstly, by direct comparison 

 with a micrometer eyepiece in a microscope ; secondly, by 

 means of a microscope fitted to the dividing engine belonging 

 to the Physics Laboratory, Melbourne University ; and, 

 thirdly, by means of a micrometer microscope at the Sydney 

 University. The following average values were obtained 

 for the radii of the sections reduced to 0° C: — 



pillary I. 

 Circular). 



First 

 Method. 



Second 

 Method. 



Third 

 Method. 



Mean 

 Values. 



Section 1 



•01905 cm. 



•01879 cm. 



•01880 



•018838 



2 



. -01929 „ 



•01919 „ 



•01899 



•019106 



„ 3 



. '01932 „ 



•01933 „ 



•01877 



•019048 



„ 4 



. '01926 „ 



•01880 „ 



•01881 



•018882 



[Mean radius (by mercury) = '018968 cm.] Mean = '018968 cm. 



