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has different values in different directions, the condition, which is 
thereby brought about, may be compared with a condition where 
the pressure has a different value in different directions. If we call 
the quantity which is to be considered as the pressure in the direc- 
tion .L to the capillary layer, pj and that in the direction of the 
capillary layer, the following formula would hold: 
J dy Co do 2 2 C 2 d'u 
AT ne ee = Pat AE ng Ba 
or 
to. “Po Ca Ek 
DD = — — 0 — TS Meern IE 
Pi—P2 ar ee eT 
This difference in pressure taken over a surface normal to the 
bordering layer, with a length of 1 em. and a breadth equal to 
the thickness of the capillary layer, furnishes the value of the 
capillary tension : 
{ (ps) dh. 
The work which is to be performed for enlarging the surface 
with 1 em.” the temperature remaining constant, so the capillary 
energy Is: 
¥ ae Bie : ( Co dg Cg do >) : 
2 = iP) n=f Te 
With the aid of this latter consideration we can easily show that 
the capillary energy is equal to the amount with which the thermo- 
dynamie potential of the bordering layer, taken over a cylinder 
whose section is | em.? and whose height is equal to the thickness 
of the capillary layer, exceeds the thermodynamic potential of the 
same mass in the homogeneous vapour- or liquid-phasis. 
Astronomy. — “Determination of the latitude of Ambriz and of 
San Salvador (Portuguese West-Africa).” By C. SANDERS 
(Communicated by Dr. E. F. van DE SANDE BAKHUYZEN). 
During a several years’ residence on the West coast of Africa I 
spent as much as I could of my leisure in making observations 
for determining geographical positions. Till now, besides a rather 
