In the article entitled "The quantic and statistical bases of visual excitation" (J. Gen. Physiol., 1947–48, 31, 269), in footnote 1, at the bottom of page 274, read, The product k (k–1) ..., may be written

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On page 284, in equation (1) add, t = mτ; m = 1,2,3....

I take this occasion to call attention to the fact that in 1944 van der Velden developed two equations, one of which described the variation of liminal energy with the flash time and the other this variation with the visual angle of the spot; both of them apply in the case of homogeneous populations of receptors (rods). These equations are very similar to mine, obtained in an entirely different manner and published nearly 4 years later. In fact, until very recently I was not aware of the equations of van der Velden, published in Physica, 1944, 11, 179, because the papers published in that journal, and particularly those which are written in Dutch, generally become known to French physiologists as abstracts which are often incomplete.

Thus the priority of the theoretical basis of the empirical laws which are directly related to the two equations in question belongs entirely to van der Velden.

ERNEST L. M. BAUMGARDT

In Vol. 31, No. 3, January 20, 1948, page 261, in equation (1) for H2 read H1.

On page 262, in equation (5) for H read H2.

On page 265, in the third line from the bottom of the page, for 4 c.mm. read 5.24 c.mm.

On the same page, in the second line from the bottom of the page, for 5 c.mm. read 6.86 c.mm.

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