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E o ee 
Fig. 9. An octant of the glass plate showing the theoretical deflection in microns 
due to the own weight. 
  
scope method. In some cases (plates of the size 23 X 23 cm) the maxi- 
mum deformations were found to be about 0.1 mm. The standard error 
of the individual measurements is of the magnitude 0.005 mm. It seems 
most important that such determinations of the flatness of glass plates 
for photogrammetric purposes are performed. 
Summary of the investigations in 1956 
From these preliminary tests it is evident that the tower method for 
checks of aerial cameras is of considerable value, in particular for 
investigations of the influence upon the geometric qualities of the pho- 
tographs from varying outer circumstances as for instance temperature, 
filters, plates or film etc and for the determination of the basic accuracy 
of the photographs. It therefore seemed desirable to continue the in- 
vestigations in 1957 for more experience. 
4. The experiments in 1957 
In 1957 the experiments were continued primarily for the practical 
tests of an arrangement for obtaining low temperature of the camera 
lens. Further tests of wide angle cameras were also performed in order 
to determine the relative accuracy between film and plates. cot WT 
4.1 Tests of an aerial camera in different temperatures 
In cooperation with the Division of Applied Thermodynamics and 
Refrigeration at the R. Institute of Technology different methods were 
tested for cooling and heating the camera. The tests were applied to the 
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