58 GEOMETRISCHE EIGENSCHAFTEN DES BILDES, DISCUSSION 
to enable everyone to secure the maximum 
economies from this source. 
Mr F. L. CORTEN: I would like to say a few 
words about the testing of aerial photography. 
The testing and checking of air photography 
and its various steps is done and has been done 
ever since air photography began. It has always 
been necessary and it has stimulated the quality 
and development in aerial survey very much. 
Excellent institutes are testing, such as the Na- 
tional Bureau of Standards, Washington, the 
National Research Council in Ottawa, the IGN 
in Paris, the Royal Aircraft Establishments at 
Farnborough, and so on, and these institutes are 
capable of carrying out all checks, testing stand- 
ards and any research which might be neces- 
sary. 
In addition, there seems to be a need for an 
international test house as has been stressed on 
many occasions. For instance, Mr Eden stressed 
it just now, not for reasons of impartiality, be- 
cause the existing institutes are perfectly capa- 
ble of carrying out exact and strictly impartial 
tests, but some of the tests and checks and com- 
parisons, as was mentioned by Dr David, Mr 
Eden and Mr Carman, are of such a character 
that they can best be dealt with by some inter- 
national institute. To pick up the thread left by 
Mr Eden, for example, we at Delft propose to 
carry out comparative tests of different films. 
Due to the time restrictions I would refer 
you to my paper, *Testing in Aerial Photogra- 
phy" where more details are given. There it is 
pointed out that we are prepared to act as such 
an international centre for testing aerial photog- 
raphy in one or more of its phases, as the need 
may indicate. Part of this work is carried out as 
research on our own initiative, but part of it can 
also be carried out in the capacity of the IT C 
Consulting Department for Aerial Survey which 
has been established recently.