Firstly I should like to apologise for Mr. Loebl’s inability to come here today. Because of illness, he has been asked to rest and since he and I are working together on the same problems, he has asked me to present this paper.

It must be obvious to all concerned in the evaluation of photographic images, that microdensitometry has rapidly changed with the advance in technology. Improvements have taken place over the years in the use and refinement of double beam recording instruments. Present trends indicate that little further can be done regarding optical resolution and diffraction limited systems can now be built. The quantitative evaluation of images based on a line integral has not changed in principle for many years. A scanning spot of the requisite size is passed across, for example, a spectral line, and the densitometric profile line gives the information required, either by its height or its area.