VISCOSITY OF WATER BY THE EFFLUX METHOD. 85 
the velocities were sufficiently small. He was under the impress- 
ion that this had not already been done, but as previously pointed 
out Jacobson had anticipated him. Although Reynolds’ experi- 
ments are not suitable for the derivation of an exact value for 
viscosity, it may be observed that his results are consistent with 
Poiseuille’s. In 1884, Réntgen' and Warburg and Sachs’ examined 
the influence of pressure and density upon this coéfficient and the 
year following Kénig® ascertained that there was no sensible 
difference in the time of efflux when it took place in a powerful 
magnetic or electric field. He made some further measurements* 
in 1887 but not by the efflux method. 
The next important contribution is Couette’s® whose experiments 
embrace two methods, viz. that of measuring the tangential force 
on an internal cylinder exerted by liquids lying between it and a 
coaxial outer rotated cylinder—method (e)—and that of efflux (¢). 
In regard to the latter it may be said that he considerably advanced 
the theory of the correction of the pressures registered by the 
manometers in the vessels at the terminals of the tubes, and 
indicated a method of observation by which the corrections may 
be entirely eliminated. Couette’s correction for the fall of pressure 
at the entrance of the capillary, though more exact than Hagen- 
bach’s 8 (1860), and very much more exact than Reynold’s s (1883) 
i evenetroted hy Bonstinesn’ in 1891 to be true 
sr “pig Einfluss des Druckes auf = ——, der Fliissigkeiten, 
—Wied. Annal. Bd. 22, p. 510-518, 1884. 
Ueber den Ristiks der Dichtigeit si ae Vinsostt tropfb 
Flunigte pfbarer 
ote iten.— Wied. Annal. Bd. 22, p 
vee ok einiger Reibu Sait HT rad View tiber den 
|-Plissigk, sas Magne tisirung und Electri: rey! auf die Reibung der 
eee oy 0 eee al. Bd. 25, p. 618 — 625, 1885. 
: bien mi ung v n Reibungscoéfiicienten tropfbarer Fliissig- 
: mittelet de Sateanes Schwingungen.— Wied. Annal. Bd. 32, p. 193 
vat eee me SS de liquides.—Annal. de Chim. et de Physique 
§ Su 
tireulaine " sais oe a iteesée dans un tube cylindrique de section 
AUX ¢ Pe aboot ’son entrée, se distribuent depuis cette entrée jusqu’ 
vit se trouve établi un régime uniforme.—Comptes Rendus, 
; Ulaire, évasé 4 son : bl t 
: entrée eg qu’ un régime sensiD! emen 
Bement dee reese’ tt de Ia dépense d e charge qu’y dniaaine V8 établis- 
PA Ne Te Teste FIL Asean ee rs ae Perea 
Mee 
