Luminous Point Research Articles

Convolution and correlation of optical signals by nonlinearoptics techniques

A method for real-time convolution and correlation of optical signals is based on the conversion of a spatial spectrum of a field due to its passage through a nonlinear medium. Examples are given of experimentally obtained convolution, auto-convolution, and correlation functions of objects representing two, three, and four luminous points.

On Fabric Gloss

Luminance distribution curves were plotted, as a light source, using a group of small bulbs set at certain distances in a hemisphere-built acryl resin plate and a parallel luminous flux from the collimeter, thereby the gloss of fabric was examined. The results obtained are:1) The luminance distribution curve for the glossing or diffusing surface illuminated with the above hemisphere light source apparatus was flat in shape.2) When the ratio of the specular reflection Is and the diffuse reflection ID is 1, the gloss can be sensed.3) As for the material with a rugged surface like fabrics, we sense the gloss at Is/ID<1. This is because the luminance points are produced by the specular reflection.

Retinal profiles. A psychophysical test of rod and cone sensitivity.

Modifications of the Goldmann-Weekers adaptometer are described which permit sensitive measurements of visibility thresholds to deep red and deep blue light. The test spots subtend six minutes of arc and fixation is controlled by a movable luminous orange point of light. Consistent measurements, usually made in the vertical meridian, suggest that data obtained with the red test spot represent cone function and data with the blue test spot represent rod function (retinal profiles). Curves are shown for eyes with normal function, color blindness, night blindness, and central defects. It appears that early damage to the macular area (as in chloroquine phosphate retinopathy) can be assessed by this method before it is observed ophthalmoscopically and before it produces notable losses in visual fields or acuity.

Measurement of the figure--effect in the third dimension by the light threshold method--front and rear visual spaces of the stimulus figure with parallel lines

It has been shown that when a stimulus figure exists in the visual field, the figure exhibits the so-called figure-effect in the form of changes in the light threshold for a small luminous point presented at places near the figure on the same front parallel plane. The finding leads to the following possibility: An effect similar to this will also occur in the depth of the visual space.For this reason, in the present study, several experiments were performed with the following two objects in view. The first object is to examine whether such an effect can be shown to exist at all. The second is to examine what tendency the effect has, if it does exist.The experimental conditions and the method of the measurement were as follows: The stimulus objects consisted of two parallel lines which were lit to form a pair of light stimuli, with three kinds of interior interval distance with visual angles of 12′, 18′, and 48′. They were constantly presented on the front parallel plane at a distance of 592.3mm from the observer. In one experiment, only one of them was presented. When the figure was presented, a small luminous point was simultaneously placed at various positions in front and the rear of the figure as shown in Fig. 2 (A), and light threshold for the point, value t, was measured. Then the threshold for the same point was measured again at the same places when the figure was not presented, as shown in Fig. 2 (B). This threshold, called t0, is a criterion value to check the degree of the elevation of the threshold t. That is, the figure-effect was examined by the difference between t and t0, and the value of (t-t0)/t0.The results obtained in the experiments were as follows:(1) It was found that the threshold values, as a whole, were higher in the depth than in the same frontal plane to the figure.(2) The threshold value was gradually elevated as the distance between the figure and the point was increased, and at a certain place far from the figure, a marked elevation was seen. Such a tendency of the elevation was observed both in the front and the rear visual spaces of the figure.(3) Such an elevation of the threshold with the increase of the distance were more pronounced as the interval distance between the two parallel lines became shorter.In view of the above results, it is concluded that the figure-effects are present also in the depth, i.e., the third dimension, of visual space, and that they also cause the elevation of the threshold as the distance from the stimulus figure increases. Such a tendency seems to be dependent upon prevailing stimulus configuration.

A new entoptoscope.

IN A PREVIOUS article1on Scheerer's phenomenon, we stated how, in the course of our research and after many trials, we had succeeded in building a simpler and better apparatus for its observation. Scheerer's phenomenon is the entoptic perception of one's own blood cells circulating in the perimacular capillaries and the closest precapillary arterioles and postcapillary venules. We refer to the luminous points as blood cells, refraining from designating them as white or red, since this is still a moot question that has received contradictory answers from various authoritative sources. There is no doubt, however, that the phenomenon is connected intimately with the blood circulation. The instrument * consists fundamentally of a metal box containing a mercuryvapor grid and a diffusing screen. On the upper part of the box there are two openings through which the light is seen. In the oculars there are filters that permit the passage of

Luminescence in Hydromedusae

The luminescent responses of Hydromedusae have been investigated by means of photoelectric recording. Animals examined included Aequorea , Halistaura , Phialidium and Stomotoca ; the first proved most suitable for experimentation. Light appears in a ring around the periphery of the umbrella. In Aequorea the luminous points correspond to yellow-green fluorescent masses in the marginal canal. The photogenic tissue in histological preparations appears as oval masses of eosinophilic cells bulging into the cavity of the marginal canal. Luminescence is intracellular. With carefully localized mechanical and electrical stimulation, light appears in one or a few restricted loci; there is no spread of luminescence around the margin. The luminescent response shows facilitation, summation at higher frequencies, and fatigue under continued stimulation. Each flash in Aequorea lasts 0⋅3 to 1⋅5 s; maximal intensity is reached in 0⋅1 s (14 to 16°C). It is concluded that the responses observed involve either direct excitation of the photocytes, or stimulation through local nervous pathways.

On the polycrystalline forms of gypsum and their optical behaviour

The paper brings to notice the remarkable optical effects exhibited by a polycrystalline form of gypsum which is different from both alabaster and satin-spar in its structure. It is not a fibrous material but consists of fine rods orientated nearly parallel to theb-axis of gypsum and exhibits a ready cleavage along planes perpendicular to that axis. A source of light viewed through a plate of the material exhibits, in general, three concentric circles which are polarised in a characteristic fashion. The source itself appears as a luminous point on the second or middle circle. It is shown that these circles arise by reason of the reflection of light at the boundaries between the rod-like crystals composing the material, for which the name “fascicular gypsum” is accordingly proposed. A theoretical explanation of the phenomena is given and photographs of the same are reproduced. Observations on the optical behaviour of alabaster and of satin-spar are also reported.

自動運動の實驗的研究

This experiment was undertaken on the assumption that the phenomenon of Autokinetic Movement was dependent for its appearance upon a central rather than a peripheral process, such as eye-movement.Two light boxes (93×70×38mm and 200×24×16 mm) were used for presenting the stimuli. One end of each of these boxes was equipped with opal glass, covered with a sheet of black cloth paper, out of which stimulus figures were cut. A miniature lamp (1.5v) was placed inside the box so that when this was on, the stimulus figures were lighted. The brightness of the lamp was controlled by manipulating the rheostat connected with it.The subject, seated about 2 meters away from the box and with his head resting firmly upon a head-rest, observed the stimulus through very small round apertures (each about 2.5mm in diameter) cut in a screen which stood close to his face. The results of his observation were reported minutely with illustrations after the manner of experimental phenomenology.The results were as follows:1. When a small arrow figure (about 1cm. length) was presented contrary to our expectations, the direction of the arrow had no influence on the direction of autokinetic movement.2. When points of light were presented, they held generally a reciprocal and intimate relationship, marking a harmonious, large-scale movement together.3. Sometimes a special and labile area was produced around the small arrow or around the two light points, and this area as a whole streamed in the dark.4. In the case of two light points the fixated point played the leading role in the whole movement and was more stable than the other. But at the presentation of a line and a point, the fixation did not produce such an effect. The line always controlled the whole movement and the point moved along the line.5. By straining and relaxing the muscles of head, jaw and arm, we found that there were some relations between autokinetic movement and the tonus of muscles. But we could not determine these relations accurately. It seems that the muscles operate as a whole, but not in separation.6. The general bodily state of the perceiver determined the manner of movement of the luminous point. To the feeling of stability of the subject himself corresponded the stability of the subject himself corresponded the stability of the autokinetic phenomenon.7. The light point came to restrain the range of movement, when the subject pointed it with his finger or held the stimulus box with his fingertips. It was easier to control the autokinetic movement by holding the box than by mere pointing. In both cases the finger played the rôle of the framework in the darkness, but for this the attention should be directed and concentrated to the stimulus.From the above, we may conclude that the autokinetic movement can be restrained or even extinguished when an object obtains an anchorage in the “object-world” which stands face to face with the “ego” or in the “ego” itself, as in our experiment with finger-tips.

Out of Focus Diffraction Patterns*

The diffraction pattern which represents the image of a luminous point produced by an instrument free from aberrations and having a circular aperture, when observed out of focus, has been calculated by A. E. Conrady, A. Buxton, and G. Lansraux. Conrady and Buxton used numerical integration. Such a process yields a sequence of values of the complex amplitude at a particular point in the diffraction pattern for a particular lack of focus, and for any given integration, the distance W of the point under consideration from the center of the pattern, and the lack of focus ψ, are functions of the upper limit of integration. If ψ is plotted against W, the path obtained is a parabola, ψ = aW2.The author has found a method whereby any desired path can be followed instead of a parabola. In particular, if the point of observation is near the edge of the purely geometrical diffusion disk and remains at a constant distance from it as ψ changes, then, for large values of ψ, the form of the diffraction fringes is approximately independent of ψ and their intensity is inversely proportional to ψ2.

CHAPTER I: Earlier investigations concerning the star figures seen surrounding distant luminous points

Acta OphthalmologicaVolume 26, Issue S30 p. 9-11 CHAPTER I: Earlier investigations concerning the star figures seen surrounding distant luminous points First published: February 1948 https://doi.org/10.1111/j.1755-3768.1948.tb05308.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume26, IssueS30February 1948Pages 9-11 RelatedInformation

The Place of X-ray Crystallography in the Development of Modern Science

VON LAUE'S discovery of the diffraction of X-rays by crystals effectively provided science with a new eye with which to see the ultimate arrangement of the nuclei and electrons of solid matter. It is true that X-ray analysis does not show atoms and electrons to the eye in the way that a microscope does; the process of interpretation is more complicated, but it is essentially analogous. In an ordinary optical instrument the interference of rays from luminous points is used to build up the optical image by means of a lens system. In X-ray analysis the interference pattern is taken and interpreted mathematically instead of optically to give the nature of the object observed, so that it is just one step farther removed from our inherited mechanism for appreciating the external world. Now we have had this new eye only seventeen years, and although it has shown many marvellous things and enabled us to build for the first time a picture of the intimate structure of solid matter, we cannot believe that it has more than begun to be used. Many more important discoveries are bound to follow from it, and it has still to find its place as an essential instrument in every branch of scientific research. The object of this article is to point out what can already be seen of its possibilities and how it is likely to affect science in the near future. The Three Forms of Information from X-ray Diffraction Apart from the knowledge given on the nature of X-rays—which was of such critical importance in the discovery of atomic numbers and in the verification of Bohr's quantum theory of radiation—the diffraction of X-rays by crystals yields information about three grades of fine structure of matter. Ultimately the diffraction of X-rays is due to the interaction of the radiation with the electrons in the atoms of matter, and so the deepest information it can give is on the position of the electrons in the individual atoms, or, more correctly, information as to the average distribution of density of negative electricity. Here it is most closely related to pure physics and leads to the possibility of the complete description of the state of any piece of matter. But without going nearly so deeply, X-rays can show the position of the maxima of electrical density, that is, the position of each kind of atom, in a regular crystalline structure. It is in this field that the chief work of X-ray crystallography has been done. It is faced with the extensive problem of determining all the different possible types of atomic arrangement in solid substances, which has such a clear bearing on chemistry.

IV. — Aberration diffraction effects

The image of a luminous point, given by a symmetrical optical system, will not itself be a point; and this will follow both from the nature of light and also from the necessary ‘ imperfections ’ of the system. A part only of the incident wave will pass through the system and diffraction phenomena will appear ; in addition the emergent wave will not be a portion of a sphere but will be distorted by the geometrical aberrations of the system. Diffraction theory would indicate that corresponding to a point source of light a system of luminous rings should be produced upon the image plane ; this was investigated by Airy in 1834 ; geometrical theory, on the other hand, leads to a consideration of several types and orders of aberration, the more common ones being better known as the 'Five Aberrations of Von Seidel.’ They are: Spherical Aberration, Coma, Astigmatism, Curvature of the Field and Distortion ; these are well known and they have been investigated by a number of writers. In the present paper a consideration is undertaken of the modification of the ‘ ideal ’ diffraction pattern produced by these geometrical aberrations. The method adopted depends upon the Eikonal Function of Bruns, and a summary of the properties of this function is given, therefore, in Part I of the paper ; Part II deals with the Aberration-Diffraction effects. Throughout Parts I and II of the paper it is assumed that the stops of the optical system are circular, with centres upon the axis of symmetry ; and this is generally the case. Occasionally, however, other stops are used, and in Part III of the paper is undertaken a consideration of the diffraction effects of such. The precise forms of aperture considered are the following :— 1. the usual circular aperture with the central portion stopped out—as suggested by Lord Rayleigh : 2. one (or two parallel) narrow rectangular apertures—as used for the determination of the diameters of large stars and for the separation of close double-stars : 3. a semi-circular aperture—as used in a heliometer.

V.—Symposium—The Time Difficulty in Realist Theories of Perception

Is the time intervening between stimulus and perception an obstacle to a realist theory of perception ? The question is not a new one. It is one of the ordinary difficulties that the idealists have urged against the realists, but it has a special significance in relation to recent developments of physical theory. The electro-magnetic theory has established the fact that there can be no immediate action at a distance, a time interval intervenes between the emission and the reception of a luminous or any other kind of signal. Neither light nor gravitation nor any other kind of influence of one object on another is instantaneous. When the rays from a luminous point impinge on the different parts of my retina I perceive the point whence the rays are coming. The perception seems to me the immediate apprehension of this point, and to be there in space where the point is. But this is impossible, for the rays I perceive are not at this point when I perceive it. The object of visual perception can never be actually present to me, for no signal can travel more quickly tharl light and so make me aware of the object before I receive the luminous signal. If the point is on the sun, the light wave takes eight minutes, if it is on Sirius it takes about eight or nine years, and if on more distant stars, hundreds or thousands of years. On the other hand, however close to me it is, it must occupy some time, even though it be the quite inappreciable infinitesiinal fraction of a second.

On the formation of multiple images in the normal eye

It is well known that a small bright object for which the eye is not accommodated often presents a multiform appearance, the number of separate images perceived varying in different cases from about six to fifteen. In Helmholtz’s ‘Physiological Optics,’ drawings are given illustrative of the phenomena exhibited by a luminous point when the conjugate focus is situated a little in front of or a little behind the retina. A narrow luminous line such as that formed when a spectroscope slit is held before a flame or other bright background may become similarly multiplied.

Are Röntgen Rays Polarised?

MR. L. CASELLA has made for me a Crookes' tube having as the anode a platinum window sealed into the end of the tube opposite the kathode, which is the ordinary aluminium disc. Owing to the glass sealing, only a small portion of the platinum, about 3 mm. in diameter, is free to act. The light from all but this portion was screened off by thick glass discs and a brass disc, these having each an aperture in the centre. The result, with the fluorescent screen, was at first poor, because the vacuum was too low; but as that got higher it improved, and I was able to electrograph a part of the hand, by the rays given off by this small platinum window, in 15 seconds, the plate being 2½ from the window. An ordinary focus tube takes 30 seconds to produce the same effect under similar conditions, but gives better definition. With the platinum window tube, though the bones are defined on the fluorescent screen, there seems to be too much white light, and the difference between bones and flesh is less marked. The tilted platinum of a focus tube, apparently, reflects most of the kathode rays, but transmits some. Compare the behaviour of the platinum in both tubes with the action of 9 light on glass. With both glass and platinum, part of the rays are transmitted and part reflected, the proportion varying with the angle of incidence; but, with both, those rays which are perpendicular are apparently transmitted. If the glass be tilted at the proper angle, the reflected rays and a small part of the transmitted rays are polarised. Suppose the plate of glass in the position of the platinum window, and the source of light a luminous point within the tube; although most of the transmitted light would be radiated direct from the luminous point, part would be rays which had been polarised by reflection from the walls of the tube. The analogy would still hold good, for we know that, as far as X-rays are concerned, glass behaves very similarly to platinum, for these rays are under suitable conditions given off by both.

The Spectrum of Helium1

IN the Chemical News for March 29 last (vol. Ixxi. p. 151), I published the results of measurements of the wave-lengths of the more prominent lines seen in the spectrum of the gas from clèveite, now identified with helium. The gas had been given to me by the discoverer, Prof. Ramsay; and being from the first batch prepared, it contained other gases as impurities, such as nitrogen and aqueous vapour, both of which gave spectra interfering with the purity of the true helium spectrum. I have since, thanks to the kindness of Profs. Ramsay and J. Norman Lockyer, had an opportunity of examining samples of helium from different minerals and of considerable purity as far as known contamination is concerned. These samples of gas were sealed in tubes of various kinds and exhausted to the most luminous point for spectrum observations. In most cases no internal electrodes were used, but the rarefied gas was illuminated solely by induction, metallic terminals being attached to the outside of the tube.1 For photographic purposes a quartz window was attached to the end of the tube, so that the spectrum of the gas could be taken “end on.”

Measurement of Jupiter's Satellites by Interference

IT has long been known that even in a telescope which is theoretically perfect, the image of a luminous point is composed of a series of concentric circles with a bright patch of light at the common centre. This system of circles can easily be observed by examining any bright star with a telescope provided with a circular diaphragm which diminishes the effective aperture. The appearance of the image is shown in Fig. I, a. In the case of an object of finite angular magnitude the image could be constructed by drawing a system of such rings about every point in the geometrical image. The result for a small disk (corresponding to the appearance of one of the satellites of Jupiter as seen with a 12-inch telescope whose effective aperture has been reduced to six inches) is given in Fig. 1, b; the chief points of difference between this and Fig. 1, a, being the greater size of the bright central disk, and the lesser clearness of the surrounding rings. The larger the disk the more nearly will the appearance of the image correspond to that of the object; and the smaller the object the more nearly does it correspond with Fig. 1, a, and the more difficult will be the measurement of its actual size. Thus, in the case just cited, the actual angular diameter is about one second of are, and the uncertainty may amount to half this value or even more.

MEASUREMENT OF JUPITER'S SATELLITES BY INTERFERENCE

IT has long been known that even in a telescope which is theoretically perfect, the image of a luminous point is composed of a series of concentric circles with a bright patch of light at the common centre. This system of circles can easily be observed by examining any bright star with a telescope provided with a circular diaphragm which diminishes the effective aperture. The appearance of the image is shown in Fig. I, a. In the case of an object of finite angular magnitude the image could be constructed by drawing a system of such rings about every point in the geometrical image. The result for a small disk (corresponding to the appearance of one of the satellites of Jupiter as seen with a 12-inch telescope whose effective aperture has been reduced to six inches) is given in Fig. 1, b; the chief points of difference between this and Fig. 1, a, being the greater size of the bright central disk, and the lesser clearness of the surrounding rings. The larger the disk the more nearly will the appearance of the image correspond to that of the object; and the smaller the object the more nearly does it correspond with Fig. 1, a, and the more difficult will be the measurement of its actual size. Thus, in the case just cited, the actual angular diameter is about one second of are, and the uncertainty may amount to half this value or even more.

The Cross as a Sun Symbol

THE use of the cross as a sacred symbol dates from the earliest times, and is almost universal. It occurs upon the monuments and utensils of every primitive people from China to Yucatan. In many, perhaps in a majority of, instances it is used as a symbol of the sun. One of the oldest and most widely occurring forms is the cross with crampons turned to the right or left, the svastika and sauvastika of India, the “Thor's hammer” of Western Europe. Prof. Max Muller thinks that the svastika represents the vernal sun, and is hence an emblem of life, health, and creative energy (Schliemann's “Ilios,” p. 348). Mr. Edward Thomas (ibid.) believes it to have arisen from the conception of the sun as a rolling wheel. The Chaldean sun symbol was first a circle, then a circle with an inscribed cross. The symbol of the sun-god at Sippara is a small circle with four triangular rays, the four angles between being occupied by radiating lines, and the whole circumscribed by a larger circle. The same symbol occurs repeatedly upon the shell gorgets of the mound-builders (Second Annual Report of the U. S. Bureau of Ethnology, plates liii., lviii., and lix.). The peculiar figure repeated upon the facade of the “House of the Nuns” at Uxmal seems to be a conventionalised circle and cross with rays. The Moqui symbol for the sun is a Greek cross with a small circle at the centre, in which are three marks to indicate the eyes and mouth of a face (First Annual Report of the U. S. Bureau of Ethnology, p. 371). It is needless to multiply examples: the important question is, How has the cross come to be a symbol of the sun? If anyone will observe carefully a lamp, or other bright light, with partially closed eyes, the answer will be obvious. The rays which appear to proceed from the luminous point always form a cross of some kind. A little experimenting will show that this appearance is due to reflection from the eyelashes and edges of the eyelids. The same experiment may be tried with the sun itself: if observed when considerably above the horizon, squinting will be unavoidable. If the head is erect, the downward arm of the cross will be much the strongest, and the upward arm may be obsolete; but if the head is thrown back, the arms will be nearly equal. The evolution of the sun symbol seems to have been as follows: He was first represented by a circle or disk as he appears when near the horizon; observations made when he was shining brightly revealed the crossed rays. This led to a combination of the circle and cross. If this hypothesis be correct, the svastika was originally neither a rolling wheel, nor, as Burnouf supposes, the crossed sticks from which our ancestors elicited fire; but it is a modification of the circle and inscribed cross.

Focal Lines

WHEN a pencil of light proceeding from a luminous point is incident upon a prism, the rays after refraction do not as a rule diverge from a point, but from two short lines at right angles to each other at some distance apart depending on the angle of incidence of the pencil. These lines are known as the focal lines of the pencil. If the edge of the prism be vertical and the axis of the pencil He in a horizontal plane, the focal lines are respectively horizontal and vertical. The position of the horizontal line is independent of the angle of incidence of the pencil, its distance from the prism being the same as that of the luminous point, or with the notation of Parkinson's “Optics”(p. 88)—