VISCOSITY OF WATER BY THE.EFFLUX METHOD. 95 
1 
93 7? ia 5 seed p g” 
Q's « L q 
p being the absolute density—grammes per cubic centimetre—of 
1) oles 
the effluent. This will more clearly exhibit the reduction of the 
pressure if put in the form 
ay a { Pe 
| Shel” (ka: RK) 
so that the term in brackets denotes, according to Hagenbach, 
what might be called the reduced pressure,! say P,. Hagenbach 
justly observed that this correction more particularly applied where 
the end of the tube is in the form of a conoidal adjutage. Since 
we propose to consider the value of the coéfficient of the correction, 
the reduced pressure P, may with greater generality be written— 
PG Py £22 (3) 
T 
According therefore to Hagenbach the value of the factor m for 
@ conoidal terminal is, 
m = 2-5 = 0-79370 
‘ Reynolds,’ remarking that Poiseuille, though he measured the 
_ pressures in the vessels supplying and receiving the flowing liquid, 
-“hevertheless neglected the correction, states that, if U denote the 
Mean velocity in the pipe and g the acceleration of gravity, it will 
~ either U* (2g) or 1-505 U? /(2g) according as the entrance 
; pemial of the tube is trumpet-shaped or cylindrical. He also 
ys that, as Poiseuille definitely affirmed the latter condition to 
v5 been realized in his experiments,? the application of the 
“orrection would have made them consistent,' a dictum however 
Se  —— 
It is hereinafter show 
n that Po, may be generally supposed to be 
; (2), but that this su ition may be set aside b 
— evidences of its : 7 . y 
; a ’s treatise, p. 439. La soudure est faite de telle sorte 
avee du + utube D (the capillary) se dilatant ex abrupto, est en rapport 
enflement G (a bulb at the end of the tube forming the reservoir 
_ fIse ct, p. 981, 
