As there is such a close analogy between the kodak and theeye, an extensive series of investigations is being carried on in physiological optics in this laboratory and this paper gives a brief summary of some of the results obtained up to this time. By making a detailed study of the functions of the eye it is hoped that some information may be discovered relating to some of the new uncertain points in photography.
The eye and the photographic plate are the most widely used instruments for studying light problems, and in practically all cases the final judgments are rendered by the eye. The eye operates through a range of ten billion to one, and maintains a remarkable efficiency throughout a greater part of this extensive range.
By knowing the efficiency at which the eye operates we are able to determine the accuracy to which photographic results may be determined.
In this research one of the problems studied was the least amount of physical radiation which will give rise to a, perception. This depends on several factors, the greatest of which is the adaptation of the eye. When the eye is fully adapted to absolute darkness its sensibility is the greatest, and the threshold obtained under this condition gives the absolute photochemical rea#ctivity of the retina.
When viewing a r-mm. spot at a distance of 3 metres the minimum radiation visually perceptible was found to be 17 x 10-l~ ergs per second.
When the test-spot was increased to a s-cm. square and the observing distance was 3 j cm., a dask-adapted eye could just perceive a brightness of * Communicated by the Director. lcommunication No. 52 from the Research Laboratory of the Eastman Kodak Company