Absence of Dispersive Properties of Space for Electromagnetic Radiation Tested to ± 14 x 10^-5; Comments on a Proposal of Softky and Squire

In session I 1 of the Berkeley meeting of December 30, 1960, S. D. Softky and R. K. Squire proposed a test for dispersive properties of space for electromagnetic radiation by detonating a nuclear explosive at a distance of 10^6 miles from the earth and noting the arrival times of different types of radiation at detectors above the atmosphere. The purpose of this note is to point out that Softky and Squire have overlooked the fact that a test for the dispersive properties they postulate already exists, covering perhaps not quite as extensive a range of the electromagnetic spectrum as they hope to cover (they claim a factor of 10^11) but nevertheless sufficient to render any such effect extremely unlikely over a range of frequencies of a factor of 5 X 10^9. I refer to a measurement performed in 1950 by means of the bent quartz crystal diffraction spectrometer [1] of the wavelength of the annihilation radiation generated in a block of copper by positrons from the nuclide 64Cu

A new Parallel Plate Comparator

The "Parallel Plate Comparator" is best adapted for measuring the separation of two parallel lines (eg. spectral lines) whose structures are practically identical and which are on the same negative and only a few millimeters apart. It consists of two plane parallel plates of glass attached to a mechanism such that they can be set at equal and opposite angles with the plane of the negative. The two equal and opposite angles between the plates and the negative must lie in a plane normal to the lines whose separation is to be measured. The lines are viewed through the inclined glass plates with a long focus microscope having a sufficiently large field to include both plates and both lines. The lines are brought into apparent coincidence in the field of the microscope by varying the obliquity of the glass plates to the line of sight. This obliquity is then a measure of the separation of the lines. If the lines are of identical structure and intensity, even though they are not symmetrical in structure, much greater precision is possible by bringing them into apparent coincidence than by attempting to set a crosshair first on one line and and then on the other. (The lines should be photographed or blocked off so that the upper half of one and the lower half of the other only is visible. The slightest fault in the apparent coincidence of the ends of the two half lines is then glaringly evident through the microscope. When coincidence is obtained, the two half lines give a good photometric match across their juncture and appear as one. In a properly designed instrument, the crack separating the two plane parallel glass plates is invisible because it is not in the focal plan of the objective.

The "Palace of Discovery" at the Paris Exposition of 1937

During the summer of 1937 it was my pleasure and privilege to visit on many occasions the "Palace of Discovery" of the Paris Exposition. This vast, splendid and instructive exhibit of scientific principles and progress was essentially the idea of that "grand old man" of French science, Jean Perrin. The details were admirably worked out with the wholehearted cooperation of many of the most important French scientific workers who gave freely of their time and energy

A High Resolving Power, Curved‐Crystal Focusing Spectrometer for Short Wave‐Length X-Rays and Gamma‐Rays

Description is given of a transmission‐type, curved‐crystal focusing spectrometer for short wave‐length x‐rays, and gamma‐rays having a dispersion of 1.186 x.u. per mm at short wave‐lengths. The spectrometer utilizes the (310) planes of quartz in a crystalline plate of dimensions 80×70×1.0 mm curved cylindrically to a radius of two meters. High luminosity is obtained since the useful aperture in the crystal holder has an area of 10 cm2 and subtends 0.00025 stereradians at the focus. It also affords high resolution since by photographic tests with x‐rays the curved plate has been shown to focus a specified x‐ray wave‐length to within 0.06 mm of the same position on the focal circle for all parts of its useful aperture and over the entire operating wave‐length range. The geometry of the mechanism permits absolute measurements with a precision screw of the sine of the Bragg angle on both sides of the reflecting planes, affording a wave‐length range which includes at longest wave‐lengths the K‐spectrum of silver and goes down to zero wave‐lengths. For short wave‐length gamma‐rays the source is placed at the focus. A multiple‐slit collimator of tapering die‐cast lead partitions spaced apart with tapering separators, is used at short wave‐lengths to transmit the monochromatic diffracted beam and absorb the directly transmitted and scattered heterogeneous beam. The present collimator limits the spectrum that can be studied to a shortest wave‐length of 7. x.u. corresponding to 1.75 Mev. The intensity of the diffracted beam is to be measured with a special multi‐cellular G. M. counting tube of high efficiency, provided with a number of thin lead partitions through which the beam passes successively. In photographic spectra made with this instrument the tungsten and also the silverKβ_1β_3 doublet is completely and clearly resolved. Reproductions of such photographic x‐ray spectra are shown in which the line breadths have substantially the natural breadth. Fluorescence spectra of silver have been made in 10‐minute exposures. A companion paper gives the all‐important precision technique of generating the curved cylindrical stainless steel clamping blocks for the crystal

Improvements in the precision of beta-ray spectroscopy

The direct measurement of gamma‐rays only yields about half the picture in the study of nuclear energy levels. The other, and indeed to most physicists more familiar, half concerns the β‐rays, including in this term both the continuous β‐ray spectrum and the line spectrum by “conversion”, either internal or external. Ever since 1948, therefore, we have been much occupied with the design and construction along rather novel lines of a high precision helical focusing magnetic β‐ray spectrometer planned as a companion instrument to the crystal diffraction spectrometer as regards absolute precision and accuracy. We have only very recently completed this instrument and made the first tests on it which indicate that it will meet all our expectations both as to high absolute accuracy and high luminosity and sensitivity to weak sources. The beta‐ray spectrometer discussed in the following pages has recently been completed at the California Institute of Technology. It is shown in cross section on the cover

Present Status of Precise Information on the Universal Physical Constants. Has the Time Arrived for Their Adoption to Replace Our Present Arbitrary Conventional Standards?

Three years ago Dr. E. R. Cohen and I prepared and published our latest (1955) least-squares adjustment of all the most reliable data then available bearing on the universal constants of physics and chemistry. Since then new data and information have been accumulating so that a year or two from now the time may perhaps be propitious for us to prepare a new adjustment taking the newly-gained knowledge into account. At present it is too early to attempt such a re-evaluation since many of the investigations and re-determinations now under way are still far from completed. I shall be obliged, therefore, to content myself in this talk with a description of the sources of information upon which our 1955 evaluation was based, mentioning however, the weak points where these are now either well established as errors or at least considered to be under strong suspicion of systematic error. I shall also tell you a little of some of the new re-evaluations now under way

Pilgrims' progress in search of the fundamental constants

The practice of making broadly inclusive surveys, from time to time, of the status of our knowledge of the fundamental constants of physics and chemistry may be said to have started with a famous paper by Raymond T. Birge, of Berkeley, published in Reviews of Modem Physics in 1929. To Professor Birge, also, is due the credit for being the first, as far as I know, to apply the method of least squares in order to determine most probable values of three of the constants; e, the electronic charge m, the electron rest mass; and h, Planck's constant, using a highly overdetermined set of experimental data on functions of these three quantities. The fundamental constants of nature are so interrelated that a measurement affecting one affects them all. The author became interested when Millikan's oil‐drop value of the electron charge was different from the value given by x‐ray determination of crystal spacings. To assist in finding the true values, he invented a method for plotting various functions of the constants in a space of as many coordinates as there are constants. If all measurements are consistent, the plotted functions intersect in a point. When they do not intersect, one examines standard deviations, which correspond to thicknesses of surfaces, in an effort to find out what is wrong. In three decades, searches of this kind have reduced uncertainties in the constants from a fraction of a percent to, at most, tens of parts per million

Two applications of the sylphon bellows in high vacuum plumbing

The term "vacuum plumbing" is intended to express briefly the mass of technique which has recently been developed by which vacua from 10^(-4) to 10^(-6) mm Hg or better are obtained in systems mainly of metal and of large volume. The large high voltage x-ray tubes and ion accelerating tubes of C. C. Lauritsen at the California Institute of Technology, E. O. Lawrence at Berkeley and Merle Tuve at the Bureau of Terrestrial Magnetism are three examples of such systems

Conditions for Optimum Luminosity and Energy Resolution in an Axial β‐Ray Spectrometer with Homogeneous Magnetic Field

In a β‐ray spectrometer with axial homogeneous magnetic field, it is shown that optimum energy resolution and luminosity are obtained when the trajectories make an angle close to 45° with the field and that an annular resolving slit should be provided at a determined radial and axial location relative to the source. The combined effect of three independent sources of instrumental energy line width is analyzed for the optimum condition. Formulas are given for the optimum dimensions, the energy resolution and the luminosity