S. I. VAVILOV, The Eye and the Sun. On light, the sun, and vision, 2nd ed. GTTI, M.–L., 1932, 64 pp., price 2 rubles.

Among the enormous number of popular books on optics, the small book by S. I. Vavilov occupies a special place. Written in a meaningful and brilliant manner, it is one of the very few popular books that will be read with keen interest and great benefit both by the established specialist and by the beginning student. An idea of the contents of the brochure may be obtained from its concluding paragraph, which says the following: “The fundamental feature of the eye is its adaptation to a definite energy, the presence of ‘daytime’ and ‘nighttime’ vision, and the selection of the visible portion in the boundless spectrum—all this is the result of the adaptation of the eye to sunlight on earth. The eye cannot be understood without knowing the sun. Conversely, from the properties of the sun one can, in general outline, theoretically infer the features of the eye without knowing them in advance.” The reader will find in this brochure a whole series of vividly and engagingly presented facts relating both to the very latest successes of optics (wave mechanics, for example) and to its history (Ch. 1); in the 2nd and 3rd chapters information is given from the physics of the sun and the physiology of our vision, necessary for substantiating the above-cited principal thesis of the brochure. This brochure will undoubtedly go through more than one edition, and therefore it is worth pointing out here also a few accidental oversights that should be corrected in subsequent editions.

In the text explaining Fig. 34 (reading speed as a function of illumination), it is stated that the “intensity of illumination” is plotted along the axis of abscissas in meter-candles (lux). In fact the intensity of illumination is expressed here in foot-candles, and therefore the increase in reading productivity ceases at a significantly larger number of lux than is indicated in the text: not at 16, but at 172 lux. Thus the author’s conclusion also falls away: “There is no practical sense in further increasing brightness (above 16 lux.—N. F.).” (Fig. 34 was borrowed by the author from Schulz’s book Das Sehen, where it is given incorrectly.) On pp. 57–58, where the expediency of the structure of the eye is explained, Figs. 35 and 36 give curves of energy distribution in the spectrum of the sun with a maximum between 700 and 800 mμ, contradicting what the author himself gives earlier (pp. 30 and 32). These curves depict the distribution of energy in the prismatic spectrum, and therefore, of course, cannot serve as a basis for the considerations developed by the author on these pages. In particular, if one takes the chlorophyll spectrum given on p. 58, then the maximum of solar energy will lie near the minimum of the chlorophyll absorption curve. If, instead of the curve in Fig. 35, one takes the curve given by the author earlier, on p. 30, then the “sun-likeness” of the eye turns out to be still more striking. Namely: the maximum of the “visibility” curve lies at 556 mμ, while the maximum of the curve of energy distribution in the solar spectrum (according to Abbot’s data for the December Washington sun) lies around 550 mμ. The first phrase of the third paragraph on p. 46 should have been changed to read: “defects of the eyeball (elongation in the axial direction) and of the natural lens…,” since the former is encountered much more often as the cause of nearsightedness and farsightedness than the defects of the crystalline lens indicated by the author. In Fig. 38, in accordance with the text, what should have been given is not the curves of elementary stimuli, but the curves of the “principal sensations.”

All these remarks in no way diminish, of course, the value of this excellent little book, to which one can only wish the widest possible circulation.

N. Fedorov