PHYSICAL FACTOR RESULTS 99 
tained from the ecograph which makes it possible to get the exact mean 
from the sum of all the hour readings. When it comes to the seasonal 
mean, the ecograph is even more necessary, exception being made for 
‘water-content, in which case a number of readings on various days through 
the season will suffice. The value of factor means for diagnosis and for 
curves has already been sufficiently commented upon, and the feasibility of 
factor sums already indicated. 
