Page:Journal of the Optical Society of America, volume 30, number 12.pdf/82

 DECEMBER, 1940

1. Refractive Indices of Liquid Aliphatic Organic Compounds. , Research Laboratories, Eastman Kodak Co.

The molal refraction, defined by a Gladstone-Dale type of equation, R=V(n$D$-1), where V is the molal volume and n$D$ is the refractive index for the Na D lines, is, for a normal paraffin, a rectilinear function of the chain length. For any paraffin, the molal refraction is, practically within experimental error, the sum of “bond refractions,” each of which has a magnitude depending on the kinds of atom (hydrogen; primary, secondary, tertiary or quaternary carbon) joined by the bond. The molal refraction of an unsaturated aliphatic hydrocarbon can be computed from that for the corresponding saturated compound by subtracting a characteristic constant for each double or triple bond (the size of the constant depending somewhat on the number of R groups attached to the multiply bonded atoms) and adding another constant if two multiple bonds are adjacent to or conjugated with each other. The molal refraction of many derivatives of aliphatic hydrocarbons can be computed quite accurately by adding appropriate constants, characteristic of the substituting atoms or groups, to the refractions calculated for the corresponding unsubstituted compounds. Constants have been derived for chlorides, bromides, iodides, amines, alcohols, ketones, aldehydes, acids, esters, ethers, thio-ethers, etc. Equations are presented for the calculation, for compounds of the various classes discussed, of molal refractions from the structural formulas.

2. The Regulation of Tungsten and Mercury Lamps., University of Rochester.

Certain radiometric problems attempted here have required the regulation of high intensity tungsten lamps and of mercury arc lamps. Voltage, current, resistance, radiation, and power d.c. regulators were developed for tungsten lamps. Voltage regulation was chosen. A 1500-watt 115volt tungsten lamp in series with a resistance bank of heater coils is connected to the 220-volt line. In parallel with the resistance bank are six power tubes. Differences in the lamp voltage from a reference voltage are put into a two-stage d.c. amplifier and the output is applied to the grids of the power tubes in such a way as to increase the power tube current when the lamp voltage decreases. Fluctuations in the voltage output of the local generator are several percent, but regulation of lamp voltage is about 1/400 of one percent. However the radiation output of the lamps is not better than 1/10 of one percent due to several causes within the lamp itself. The radiation output of the type H5 mercury arc lamps has been regulated to better than 1/10 of one percent for short periods (30 minutes) by a photoelectric regulator. Six power tubes are connected in parallel with the lamp across the secondary of the lamp’s transformer. Light from the lamp falls on a photo-cell in series with 100 megohms which operates into a one-stage feed-back amplifier. The output of the feedback amplifier goes to the input of a three-stage d.c. amplifier the output of which controls the voltage on the grids of the power tubes in such a way as to decrease the current in the power tubes when the photo-current decreases. Without the regulator, radiation fluctuations are several percent. When the regulator is to be used for long periods a thermopile or other such device is used as a reference standard.

3. Factors Contributing to the Discrepancy Between Subjective and Skiascopic Determinations of the Refraction of the Eye. , Ohio State University.


 * J. P. C. Southall, “Optical principles of skiametry,” J. Opt. Soc. Am. 13, 245-266 (1928).

An eye can be rendered artificially emmetropic by placing before it an ophthalmic lens which corrects the spherical and astigmatic errors of refraction. When such an eye is subjected to skiascopic examination at a distance of, say, 40 cm, the eye can be made to fixate a target in the same plane as the skiascope, and although the subject reports that the target is seen clearly, the skiascope will indicate that the eye is under-accommodated. Conceivably, the following factors might contribute to this discrepancy between subjective and skiascopic criteria of the state of refraction: (1) displacement of the skiascope from the line of sight; (2) the lazy lag of accommodation; (3) spherical aberration; (4) chromatic aberration. The paper reports an investigation of the relative roles played by these factors. A special type of skiascope and an instrument called an aberrometer have been designed for carrying out the investigation. These two instruments make it possible to evaluate the roles played by the different factors. The displacement of the skiascope from the line of sight was not found to be an important factor, and the discrepancy between the subjective and skiascopic determinations of the eye involves to a certain extent all the other factors mentioned above.

4. Ophthalmic Lens Testing Instrument. , Dartmouth Medical School.

In the study of the importance of the relative sizes and shapes of the ocular images in the two eyes to binocular vision, it is necessary to have an instrument with which the optical properties of lenses, as used with the eyes, can be completely determined. Since no existing instrument was adaptable, this necessitated the building of one. The present paper briefly describes the instrument from the point of view of measuring power, astigmatism, peripheral aberrations, prismatic deviation, magnification and distortion for the lens used with the stationary and mobile eye. An example of the measurements is given. (There are two such instruments at the present time—one at Dartmouth,