VI

DISCUSSION OF RESULTS

In order to emphasize the great diversity in the conclusions
reached as a result of the various investigations already referred to,
the following brief summary is given.

1.  Konig and Broca and Laporte agree with Helmholtz in the
view that there is no appreciable difference in acuity between illu¬
minations of different colors, nor is there any difference between
colored and colorless illumination. Failure to determine accurately
the relative intensities of illumination constitutes the chief ground
on which to question these conclusions.

2.  Uhthoff and Orum support, in general, the conclusions of the
present investigation, ascribing the highest efficiency to white illu¬
mination, with red, green and blue following in the order named.

3.  Boltunow, on the other hand, while attributing the highest
efficiency to white light, finds a decided advantage in acuity for
green illumination, as compared with red. In criticism of his work
it has already been pointed out that his test character was not well
adapted to the purpose, and that the method of looking directly
toward the source of illumination does not afford an accurate test
of acuity. This method in reality involves the perception of bright¬
ness rather than the perception of form, a distinction which is con¬
sidered elsewhere. This conclusion is in accord with the assertion of
Engelmann^ that in microscopic work green illumination yields
better results than red, but in this kind of work also observations are
made by means of transmitted light.

In seeking a theoretical explanation of the experimental data,
one is impressed with the great diversity of the factors which enter
into the problem. A few of these have already been made the subject
of separate investigation, but it is clear that the. relation of all to the
main problem will have to be determined with much greater cer¬
tainty before a satisfactory solution is forthcoming. The scope of
the present work permits only an enumeration of the more impor¬
tant of these factors, together with, in some cases, a brief reference
to the work already done in connection with them.

1. The distinction ietween the form sense and the brightness
sense has already been referred to, and the failure to observe thi^

^Engelmann:  cited by Boltunow, Zeitschrift, 1907-8, 42  (2), 359.

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