THE VISCOSITY OF WATER. 45 
—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° C.) for 
the mean radii were °018968, °018926, °020416 and °020482 
cms. respectively. 
At the conclusion of all the experiments, sections about 
4 cm. in thickness were cut from the tubes at regular 
intervals; they were ground, polished and mounted in a 
brass plate. Three independent sets of readings of their 
dimensions were obtained by me, firstly by direct com- 
parison with a micrometer eye-piece 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 micro- 
scope at the Sydney University. The following average 
values were obtained for the radii of the sections reduced 
to 0° OC. 
Capillary I. First Second Third Mean 
(Circular) Method. Method. Method. Values. 
Section 1] 01905 cm. | ‘01879 cm.| -01880 018838 
3 2 01929 | O EotoN 01899 019106 
Pee: (ON9S2) | 01933). 01877 019048 
‘3 4 OO 26 aa ONS SOi.. 01881 ‘018882 
[Mean radius (by mercury) = °018968 cm.] ; Mean =-018968 cm. 
Capillary II. | First Second Third Mean 
(Circular) Method. _| Method. Method. Values. 
Section 1 01899 cm.; :01889 01880 018862 
siti) eee ‘OSG, |, 701861 ‘01880 018763 
Peo ‘O1942 ,, 701910 01891 "019009 
ae 4 | O90Ge= 01909 01890 018990 
[Mean radius by mercury =:018926 cm.] Mean=-018906 cm. 
