Page:Journal of the Optical Society of America, volume 30, number 12.pdf/83

 Department of Research in Physiological Optics, and the second at the American Optical Company in Southbridge, Massachusetts.)


 * A. Ames, Jr., G. H. Gliddon and K. N. Ogle, ”Size and shape of ocular images. I. Methods of determination and physiologic significance,” Arch. Ophth 7, 576-597 (April, 1932); A. Ames, Jr., K. N. Ogle and G. Gliddon, “Corresponding retinal points, the horopter and size and shape of ocular images,” J. Opt. Soc. Am. 22, 614 (1932); K. N. Ogle, “The correction of aniseikonia with ophthalmic lenses," J. Opt. Soc. Am. 26, 323 (1936); E. H. Carleton and L. F. Madigan, “Relationships between aniseikonia and ametropia,” Arch. Ophth. 18, 237-247 (August, 1937).

5. Photographic Analysis of Some Unexplored Visual Phenomena., Columbia University. If an observer fixate a stationary point along the track of a speeding automobile, he will apparently see the spokes of the rotating wheels. This effect has been tentatively ascribed to stroboscopic vision, or to subjective factors. Photographs (with camera speed slow, relative to automobile velocity) show this same effect, proving that it depends on objective factors. Experiments reveal that apparent spoke visibility is limited to the lower hemisphere, that the eye must rigorously fixate a nearby stationary point, and that the effect is independent of velocity, lighting, or angle of vision. Photographs, exactly duplicating the visual impressions, are obtained by keeping the camera shutter wide open during the transit of the experimental wheel. Analysis shows that this effect depends entirely on mechanics. The apparent “spokes” are, in reality, the locus of maximum overlap (and therefore of maximum brightness) of the cycloids formed by the combined rotation and translation of each spoke. The summation of these cycloids forms a static pattern (progressively created by the combined rotation and translation of the wheel), which glides across the sentient retina or the sensitive film. Instead of demanding a stroboscopic theory of vision, therefore, this “cycloid effect” favors a theory of continuity of vision analogous to the continuous sensitivity of the camera film with wide-open shutter. A comparable illusion was described in 1821, whereby the spokes of a rapidly rolling carriage wheel, when viewed through a series of fixed vertical slits, appeared curved. Roget, in 1824, explained this effect as due to mechanical factors, and showed that the same phenomenon could be produced by a stationary rotating wheel when viewed through a transversely moving system of slits. This “Roget effect” is experimentally duplicated, and seen as a startling fixed pattern of variably curved vertical lines. Photographs made with wide-open camera shutter produce an image identical with that seen by the eye. The “cycloid effect” and the “Roget effect” are examples of the manner in which both eye and camera build up, by a summation of mechanically produced images, a retinal (or optical) pattern, which has wholly objective causality, but wholly subjective (or photographic) existence.


 * P. F. Gaehr, Science 68, 567 (1928); R. M. Packard, Science 68, 567-568 (1928); C. E. Ferree, Science 68, 645-646 (1928); J. P. Guilford, J. Exp. Psychol. 12, 259-266 (1929); H. S. Gradle, Science 68, 404 (1928); “J. M.,” Quarterly Journal of Science, Literature, and the Arts 10, 282 (1821); P. M. Roget, Phil. Trans. Roy. Soc. London 1, 131 (1825). Cited by Helmholtz, Physiological Optic (Optical Society of America), Vol. 2, p. 223.

6. A Supersonic Cell Fluorometer. , Bell Telephone Laboratories.

A method will be described for the measurement of the rise and decay of luminescence in phosphors excited by cathode-ray beams. It is particularly suited to the investigation of phosphors classed as fast, i.e., those in which the major changes in intensity occur in a few microseconds. The problem is to measure the intensity of the emitted light at definite time intervals after the excitation has started or stopped, and during periods sufficiently short so that no major changes in intensity occur within the measuring interval. This is accomplished by utilizing the properties of a supersonic cell arranged to produce the Debye-Sears diffraction effect. The high speed shutter action is obtained by modulating the supersonic wave train to produce short steep sided pulses. Time intervals in the decay process are measured in terms of distances traversed by the sound waves in water. Light intensities sufficient for direct measurement in terms of photoelectric cell response are obtained by synchronizing the periodic excitation of the phosphor with the diffracting wave pulses in the liquid. The phase relation between the excitation of the phosphor and the diffracting wave pulses may be continuously varied by moving the supersonic cell to increase or decrease the distance from the quartz crystal generating the sound waves to the section of the liquid traversed by the light beam. Several methods of using the device will be described, and some results obtained by these methods will be shown.

7. Interference Phenomena with a Moving Medium. AND, Bell Telephone Laboratories.

An experimental study of interference patterns set up on a mercury surface when the source of ripples is in motion with respect to the surface. Ripples are produced by air jets interrupted by sector disks in the air supply, and the ripple patterns, or the standing wave patterns, are photographed by intermittent and steady illumination. The air jets, light source and camera are arranged on a lathe bed so as to move with velocities which are a large fraction of the ripple velocity. The Fresnel biprism is simulated by two jets, and it is shown that the interference pattern with a moving medium is altered from that for a stationary medium in a manner which is corrected by the Fitzgerald contraction and the Larmor-Lorentz change of frequency. Stationary interference phenomena produced by the simultaneous occurrence of both capillary and gravity waves of different velocities are shown to call for the Fresnel drag coefficient to nullify effects of motion of the medium. The amplitudes of the “biprism’’ or double jet interference fringes are unaltered by motion of the medium. The question of the rate of, flow of energy in front of and behind a moving source is discussed.