This paper is the continuation of one written by the author in 1934, in which the results of binocular measurements of adaptation phenomena were reported. In the method of observation used, a patch of light seen in the right eye was compared with a second patch observed in the left eye; the right eye was then subjected to a period of light adaptation while the left was maintained in a state of constant (dark) adaptation, after which the two patches were compared again. The left eye was thus used as a reference standard against which changes induced in the right eye could be measured. The author’s trichromatic colorimeter (Wright 1929) was used in the experiments and it was arranged so that the test patch (the right eye) could be illuminated by any selected monochromatic radiation, while in the left eye a mixture of the three instrument primaries was viewed and these could be controlled to produce a match both in colour and intensity between the two patches. A further series of observations has now been made and is reported here. Some of the earlier experiments have been repeated and a great many new observations have been made, but in all the work some important improvements in the method of observation have led to a greatly increased accuracy and significance in the results and have added materially to the information that can be obtained by this method of experiment.