1388 
better than any other the fulfilment of the conditions which are 
assumed in the theoretical deduction. 
The form which we choose (diagrammatically represented in fig. 1, 
compare further fig. 2) is distinguished by the following special 
features : 
1. the pressure at both ends of the capillary tube through which 
the gas flows, can be kept constant as long as desired at any height. 
2. the mean pressure and the difference of pressure are imme- 
diately measured at both ends of the capillary. 
3. before it enters the capillary the gas flows through a copper 
tube (in our case 70 em. long) where it acquires the desired tempe- 
rature. 
The calculation of the measurements got by the transpira- 
tion method was made by the formulas of O. E. Mryer and 
M. KNupsen ©); for the amount of gas that passes through a capillary 
they give: 
Q xl = ie 46 
SS SD D == — 
8 au 1 Ps) 3 T a R 
in which 
5 Bet mM il 7 
== 1.05 — ——— and pA= Se es : 
À nl 8 0,30967 Vo 
5 a R of! 
7 = coefficient of viscosity. 
R=radius of the capillary. 
[= length of the capillary. 
t = time of flow. 
p= a —= mean pressure. 
p, = pressure at beginning of capillary. 
p, = pressure at end of capillary. 
QQ =the quantity that has flowed through, measured by the product 
of volume and pressure, and corrected for the temperature 
of the capillary. 
¢—the gliding coefficient which is determined by the two last 
equations, in which g, is the density of the gas. 
The units are those of the C. G. S. system. 
$ 3. Arrangement of the apparatus. The manner in which the 
various quantities in these formulas were determined in the measure- 
ment, will easily be understood with the help of fig. 2, 
1) M. Knupsen; Ann. d. Phys. 28, 1909. p. 75. 
