RECENT DETERMINATIONS OF THE VISCOSITY OF WATER. 187 
a? R* 
2 
P,=P-m 
equation (3) page 95, in my previous paper. Wilberforce himself 
agrees with Gartenmeister, for he also assigns the value unity to 
the factor m, regarding it as defective only by reason of the viscous 
resistance of the fluid as it approaches the tube. 
Thorpe and Rodger call the correction referred to, the Couette- 
Finkener correction for the kinetic energy of the flow.! I have 
already drawn attention to the fact, that it should be associated 
with Neumann’s name, since he deduced it as far back at least as 
1860, in the September of which year it was quoted by Jacobson 
as Neumann’s, see page 97 of my former paper; that experiment- 
ally its value appears to vary considerably ; that by kinetic theory 
Boussinesq had shewn it should be about 1°12; and that this last 
value should be used in the absence of experimental knowledge 
for particular cases. 
The examination of the circumstances of flow, near and just 
within the terminals of a tube, will probably contribute important 
results ; according to a recent number of the Journal de Physique, 
the latter element is at present being studied by Aignan.? But 
however well ascertained these circumstances are, an accurate 
evaluation will necessitate a disposition of apparatus such as will 
reduce their influence to a minimum ; this is abundantly evident 
from the discussion in Section 8 of my former paper.? 
3. Theory of correction of length of tube-—In Thorpe and 
Rodger’s paper previously referred to, Couette’s proposed correc- 
tion to be applied to the length of the tube to equate the resis- 
tances at the terminals, and to take account of the various circum- 
stances of the motion thereat, has been discussed. In the reduc- 
tion of their observations no notice has been taken of the corree- 
tion, because their values for the viscosity were found to agree 
1 phil, Trans., Vol. 185, pp. 435 - 438. 
2 Ecoulement de l’ean dans un tuyau cylindrique.—Journ. de Phys. — 
tne sér. t. 5, pp. 27, 28, 1896. 
Ppp. 93 — 103. ves : 
