( 809 ) 
the formula (8) and for which interval in the chosen time-ensemble. 
Of course this question cannot be answered. We can only remark 
that as well for the majority of all intervals in the same time- 
ensemble as for the majority of all time-ensembles (3) has the same 
value. This value is that of p for a stationary system. 
Instead of paying attention to the phases taken successively by a 
single system and to unite these to a time-ensemble we can imagine 
the path £ filled with some distribution of systems. This kind of 
ensembles I shall call line-ensembles. The number of systems on an 
element ds of the path is represented by o, ds. The line-ensemble is 
stationary if the number of points on the line does not change by 
the motion of the representing points. It is easy to indicate the 
condition necessary for g, in a stationary line-ensemble. 
Let P and P' be two points of the trajectory 4 and v and v' the 
velocity of the representing point while eg, and 9’, represent the 
density in their immediate vicinity. The number of systems lying 
on the part PP’ of ZL does not change by the motion of the sys- 
tems if 
N 1 1 
So the line-ensemble is stationary if g, is represented by 
C 
Ce Ay ee LP ee Oe ee 
The mean value of a quantity gy, having a detinite value for each 
system, can be defined by 
In this formula s, and s, denote the distance from P, and P, to 
a fixed points P, measured along the line Z. For the stationary line- 
ensemble we find 
EN em ee ee tee ev (6) 
