VISCOSITY OF WATBR BY THE EFFLUX METHOD. 79 
his regret that Euler, who in the course of his great labours often 
directed his attention to physico-mathematical problems, failed to 
treat the theory of the motion of fluids having regard to molecular 
cohesion and to some sort of internal friction (quelque espéce de 
frottement). 
The first attempt to measure the viscosity of water, so far 
as I am aware, was Lambert’s,! about 1784, and was made by 
observing oscillations in U-shaped tubes. _Coulomb’s* celebrated 
measurements by means of oscillating discs followed about 1799 
or 1800. He expressed the frictional resistance under the form 
au +bu*, w denoting lineal velocity and a and 6 constants depend- 
ing upon the physical constitution of the liquid, a form earlier 
employed by Newton,’ Bernoulli, and s’Gravesande* to express the 
resistance of the atmosphere. Coulomb practically ignored the 
influence of temperature in -his experiments, stating that between 
the limits 10° and 16° Reaum.’ its effect was insensible. Gerstner® 
however, had in 1798 noticed that the flow of water in small tubes 
varied very perceptibly with temperature, demonstrating the fact 
: by a series of experiments at Prague. In 1816 Girard’ continued 
the observation of flowin capillary tubes and deduced a formula, 
which however had no generality and must be regarded as errone- 
_ ous. Nothing in the way of experiment seems then to have been 
_ Made till about 1840, but it should be remembered that in this 
© PSS gems ye ne a a 
1 Ny j ci eae : me 
ae relativement 4 l’hydrodynamique.—Mém. 
3 ale ss! ey " 
. miences destinées & déterminer la cohérence des fluides et les lois 
tio resistance dans les mouvements trés lents.—Mém. de I’ Institut 
: a t. 3, Pp. 261. 
gp en teed au} but + cu*.—Vide the Principia Lib II. Prop. xxxt, 
by deere Newtonaniz Institutiones. 5 Loc. cit. p. 349. 
Peraturen, — die Fliissigkeit des Wassers bei verschiedenen Tem- 
th. p. 14] 78 dhm Gesell. der Wiss. Prag Bd. 3, phys-math. 
~160, 1798 
Filia 3, Mouvement des fluides dans les tubes capillaires et 
188-274, température sur ce mouvement.—Mém. I’Acad. t. 1, p. 
