Hl. de Vries

The heredity of the relative numbers of red and green receptors in the human eye

SummaryThe relative numbers of red and green cones in the human eye have been determined by an analysis of various luminosity curves. These ratios show large variations; in extreme cases one of the cones is missing (colourblindness). It is found that this ratio depends on a sex linked factor. (This was known already for colourblindness). For women the ratio proves to be the mean value of the ratios which would be caused by the two factors alone. This rule explains the wellknown heredity of colourblindness for women.

Radio-carbon dating by a proportional counter filled with carbondioxide

Synopsis A technique is described for the measurement of the natural activity of 14 carbon in a CO 2 -filled proportional counter. The following experimental details are discussed: The characteristics of the counter, the influence of gas pressure on the working voltages and on the counting rates, the effect of electronegative impurities, the background, the chemical procedure, the countertubes, the electronic apparatus and finally the possible sources of errors. The efficiency of the counter is 100 per cent in the sensitive part. The counting rate due to fresh carbon is 5.6/min, whereas the background is 3.9/min. At present the counter contains CO 2 at three atmospheres but the measurements indicate that it will be possible to increase the pressure at least up to about 15 atm. Up to now 30 samples have been dated.

Die Reizschwelle der Sinnesorgane als physikalisches Problem

A survey is given of recent work on physical aspects of sensory processes. The reasoning which leads to the generally recognized view that one rod of the retina is excited by only one quantum of light is given in par. II. In par. IIIa summary is given of the papers byHecht andVan der Velden on the number of rods which must be struck in order to obtaina sensation of light. Par. III describes the role of the quantum character of light at higher intensities (de Vries), where it sets a limit to intensity discrimination and visual acuity. The influence of Brownian movement on the process of hearing is discussed in par. VI. It is found that the Brownian movement of the inner ear is close to the threshold actually observed (de Vries), whereas the Brownian motion of the air at the eardrum (seeSivian andWhite) is below the audible threshold. The role of the Brownian movementin the sense cells is described in par. VII; the results are used for an analysis of the mechanism of hearing (see alsode Vries); evidence is obtained that electric voltages are generated in the tectorial membrane (the well-known cochlear microphonics) and that they play an important part in the mechanism of energy transfer to the sense cells (similar voltages were also derived from the cupolæ in the lateral lines of fishes by the present author). Finally some physical arguments are sumarized againstYeagleys theory of bird navigation.

The fundamental response curves of normal and abnormal dichromatic and trichromatic eyes

Abstract The results of various measurements of the sensitivity (or response) curves of the red and green receptors are discussed. The final result is that these receptors are identical with the receptors of deuteranopes and protanopes. The sensitivity curves of red and green receptors, plotted on a logarithmic scale, are parallel in the red region; for this fact a simple physical explanation is suggested. It is shown that the red receptors of protanomalous and the green receptors of deuteranomalous observers are identical, as was suggested previously by Schouten (ref. 1)). The same receptors have been found in the eyes of an abnormal deuteranope, and in the eyes of daughters of a deuteranomalous father.

On the basic sensation curves of the three-color theory.

A new method is described for the measurement of the basic sensation curves of the three-color theory of Young-Helmholtz.In order to determine the spectral distribution of the absorption of the blue receptors a weak blue spot P that mainly excites the blue receptors is projected on a field F; this field is illuminated by monochromatic light with a wave-length λ. Its energy per cm2E is increased up to the energy E(λ) where P becomes invisible. The leading idea is that the sensitivity of the blue receptors G(λ) for this light is inversely proportional to E(λ). This means that the visibility of P is better when the excitation of the blue receptors by F is small. Some restrictions are given in Section 2. In the discussion of this idea an essential assumption is that a difference in the excitation of cones or rods is never observable if the difference is smaller than 1 percent. Evidence for this law is given. When necessary, the discrimination of P by the green or red receptors is excluded by adding an appropriate amount of green light to the illumination of F. The absorption curve of the green and red receptors may be found when a green or a red spot P is used. In Section 3 the apparatus is described. In Section 4 the results of the measurements are given for the author’s left eye (deuteranomalous), for a normal trichromat, and for a dichromat. The green curve of the deuteranomalous eye lies between the normal green curve and the red curve. In Section 5 some conclusions are drawn from the measurements. It is shown that the so-called international sensitivity curve z, which has its maximum in the blue, represents the absorption curve of the blue receptors; the international curves x and y, however, must be transformed. A tentative transformation is given. Finally it is remarked that the results of our measurements are in complete variance with the so-called four-color theory.

Purification of CO2 for use in a proportional counter for14C age measurements

SummaryThe permissible amounts of impurities in carbon dioxide, to be used in a proportional counter, are of the order of one part in a million. Several different steps of purification are necessary. Our physical purification consists of condensing vapours at −80°C, whereafter the CO2 is frozen at −182°C and non-condensible gases are pumped off. About 140 simple inorganic compounds can be left after this purification. It is shown that none of these will escape from the chemical traps, consisting of furnaces with copper and silver. Special attention is paid to the inert gases, of which radon is important because of its radioactivity. In an appendix it is shown that the maximum permissible rate of flow of a gas through a cold trap is about 10/α cm3/s, α being the temperature gradient along the tube. For higher rates of flow fog will be produced that passes through the trap.

Der Einfluß der Temperatur des Auges auf die spektrale Empfindlichkeitskurve

The influence of the temperature of the eye on the spectral distribution of its sensitivity was studied. The leading idea was that the small long-wave light quanta could only decompose a molecule of the photochemical substances if this molecule had already a sufficient thermal energy. One must therefore expect the sensitivity for long wavelengths to be higher at high temperatures; moreover this influence of temperature is most pronounced for the longest wavelengths. In the measurements the sensitivity for the wavelengths of 660 mµ and 730 mµ were comparedwith each other. In the accompanying figure the slit width of the apparatus at 660 mµ is shown as a function of temperature. The experimental points are close to the lines which were predicted by the theory.

Phaserelations Between the Microphonic Crista Effect of the Three Semi-Circular Canals, the Cochlear Microphonics and the Motion of the Stapes

The phaserelations between the microphonic crista effect of the three semicircular canals of the pigeon are found to “reflect” the second law of Ewald. Evidence is obtained that the crista effect has the same phase at both sides of the crista. The cochlea effect, recorded from the round window has its maximum negative value at the moment the stapes has its maximum inward velocity for frequencies between 200 and 1000/sec. For lower frequencies the phase of the microphonic effect is ahead of the phase of the stapes.The results are discussed in relation with the model of the processes in the labyrinth organs recently developed from measurements on lateral line organs of fishes. It is shown that the second law of Ewald is a result of the histological structure of the cristae. The phaserelations between the microphonic effects of the cristae, the cochlear microphonics and the mechanical stimulus prove to be in accord with the model. The microphonics are in phase with the displacement of the cupulae (or tectori...

The resonance levels for neutron capture II1)

Abstract After a short introduction in § 1, § 2 deals with some changes made in the experimental arrangement and a thorough discussion of various corrections. § 3 gives the measurements and § 4 their discussion. They include: A. self-absorption curves for Cu (5 min period), Ag (2.3 min), Ag (22 sec), Al. B. boron absorption measurements from which resonance energies could be calculated. C. Doppler-effect for Ag (22 sec) and Cu (5 min). In the latter case, where the resonance energy is rather high (110 eV), a very definite effect has really been found. D. Activabilities both for resonance and thermal neutrons for the same elements. E. gives for the same elements and moreover for Zn (dealt with in a former paper), the different methods of calculation of the effective level width Г eff ; they are: 1. from the Breit-Wigner one level formula; 2. from the activability; 3. from scattering experiments. This is a new method, a fuller account of which will be given in a following paper, part III. In this paper only the results are used. 4. from Doppler-width. It is shown that methods 1 and 2 in many cases give too high values, as more than one resonance level plays its part. § 5 From a thorough discussion of all results it follows that the effective width Г eff does not increase at higher resonance energy, while the neutron width does not seem to depend upon the resonance energy and the atomic weight. The average distance between resonance levels for neutron capture is about 15 eV for Ag (A = 100) and about 150 eV for Cu (A = 65) in agreement with Bethes theory.

The resonance levels for neutron capture III: Scattering of resonance neutrons1)

Abstract An introduction is given in § 1. In § 2 a new method is dealt with for determining the cross-section for neutron scattering. In § 3 a theoretical treatment has been given of a new method for calculating the level width Г by relating it to the energy-loss in elastic collisions. § 4 gives the measurements and the calculation of: I. the cross-section for neutron scattering, and of II. the level width for neutron capture. In § 5 attention has been drawn to a new effect, for which the name refilling effect has been proposed: If a certain group of neutrons has been absorbed by a resonance absorber, a “hole” is present in the neutron distribution. This hole at the energy Er may be refilled by interposing a second (scattering) absorber (properly speaking, the hole is of course shifted to lower energies).