362 
We shall speak about the value of u presently. 
a l 
We may also write: oe 
r Ar 
From this we see that the greatest thiekness of the segment is 
4 
equal to =, and that it only exists for /=0; it would, therefore, 
be found if the liquid state could still exist at the absolute zero. 
Further that the mean thickness of the segment is equal to the 
mean value of the fourth part of /, and as /, and also 7, hence also 
v, is determined at given temperature, also the segment, and there- 
fore also a, is determined. 
Of the boundary of the said segment we have as yet only accounted 
for the point that lies halfway AP. To find also the other points 
we must make the line AP revolve, retaining the angle it makes 
with 45, then the point P, in the plane that we have taken as 
boundary plane between the spaces belonging to A and B, will 
describe a circle. The points [ying halfway on the lines joining A 
with the points of that circle, and which therefore also trace a 
circle on the sphere A, namely the boundary of the segment under 
Yigal; 
