Viscosity of Water. 503 



The ends A and B were connected to the reservoir of 

 compressed air or the outside air by means of three-way 

 taps. Measurements of viscosity were taken first with the 

 water flowing out of R into L, and secondly with the water 



Fig.l. 



B. 



A. 



L 



I — 10 



K 



-5 



L.0 



flowing in the opposite way, under the pressure of air in the 

 reservoir. The average of the two determinations was taken 

 as an absolute value of the viscosity. The pressure was 

 measured by means of (1) a water manometer 200 cms. long, 

 (2) a mercury manometer in cases where the pressure was 

 greater than 200 cms. of water. 



To facilitate the reading of the water manometer, a pair 

 of small parallel mirrors was attached to each of the arms. 

 These were inclined so as to make an angle of 45° with the 

 vertical manometer scale. One was fixed near the centre of 



