Volume 3, Issue 12, December 1932
Index of content:
3(1932); http://dx.doi.org/10.1063/1.1748889View Description Hide Description
The measurement of intensity of an x‐ray line presents two sets of technical requirements, quite different, according to whether the intensity is to be compared with those of other lines at the same voltage or of the same line at other voltages. The latter set of requirements is discussed here, with a description of a tube designed to meet them. This tube is built of steel and Pyrex, with several sections of each, permitting a variety of high‐voltage connections for special purposes related to possible sources of error. To prevent the deposition of carbon and tungsten on the target, the pumping speed is made very high, especially for grease vapors. The detection of carbon, and rough measurement of its retardation of the cathode rays, is accomplished by one of the special changes of connections. To minimize the effects of such positive ions as may be present in spite of the high pumping speed, the tube has a special form of cathode. And to measure the possible amount of error due to such ions, another of the special connections transforms the cathode‐ray chamber of the tube into an ionization gauge. Finally a third change of connections makes it possible to wear out the sources of minute field currents, that would otherwise cause errors in x‐ray intensity measurements.
3(1932); http://dx.doi.org/10.1063/1.1748891View Description Hide Description
A simple machine is described which quickly and automatically records on a chart the wave‐number intervals between each line in a spectrum and every other line within any desired range. Small rectangular holes are punched in a black paper tape, their positions corresponding to the wave numbers of the lines on a linear scale. This operation is rapidly carried out by means of a magnetically operated punch, working on the tape which passes over a cylinder from which wave numbers can be directly read off. The punched tape is then fed from a reel through a simple device which causes it to return on itself after passing for one meter directly over a sheet of bromide paper which is moving at right angles to the tape at a fraction of the speed of the latter. The returning tape, after passing over itself for a meter, is pulled between two rollers and stored on a reel. A set of lights is hung over the doubled tape, and whenever two punch marks come into coincidence a small rectangle on the photographic paper is exposed. Fairly high tape speeds can be used, so that a complete spectrum can be recorded in a few moments. On developing the record, the photographic paper, 40 inches wide and as long as needed, is found covered with small rectangular dots; the abscissa of each rectangle gives the interval between the two dots producing it, while its ordinate gives the actual wave number of either. Suitable marks having been punched into the tape before and after the spectrum, the calibration of the interval and wave‐number scales to compensate for any shrinkage of the record is automatically made. Those lines having any given separation in the spectrum can be quite readily picked out from the multitude of dots by means of a straight‐edge. By suitably varying the scale used for plotting wave numbers on the tape, the width of the punch marks, and the ratio of tape speed to paper speed, each type of spectrum can be treated in the most suitable manner. Where very large intervals must be recorded while a fairly open scale is still used arrangement is made for keeping a desired constant amount of slack in the returning tape, so that on one record all intervals between 30 and 2030 cm−1 might appear, on another 2000 to 4000, etc. Provision can also be made for determining from the appearance of a dot the approximate intensities of the lines combining to produce it.
3(1932); http://dx.doi.org/10.1063/1.1748896View Description Hide Description
A new optical screen has been designed for making rays of light visible to large lecture classes. The rays are made to strike obliquely across the screen, making a small angle with the plane of the screen. The behavior of rays of light incident on mirrors, lenses, and prisms can be conveniently demonstrated by using the ordinary forms of these optical devices without any special mountings. On account of the efficient utilization of the available light, this screen makes possible a large size pattern of the paths of the rays so that the pattern can be observed from all parts of a large lecture room. The rays of light are in full view of both the demonstrator and the class at all times.
3(1932); http://dx.doi.org/10.1063/1.1748898View Description Hide Description
3(1932); http://dx.doi.org/10.1063/1.1748899View Description Hide Description
3(1932); http://dx.doi.org/10.1063/1.1748901View Description Hide Description
3(1932); http://dx.doi.org/10.1063/1.1748902View Description Hide Description
An infrared spectrometer is described which has the following features: (1) The entire optical path may be evacuated to about 10−4 mm of mercury pressure by the use of charcoal cooled with liquid air. (2) Exit and entrance slits are both adjusted from outside the vacuum by a single graduated head. (3) The optical system is arranged to use one mirror for telescope and collimation with the slits arranged on its optical axis. (4) The prism (or grating) is rotated by a 10‐inch lever actuated by an ordinary micrometer. This lever connecting the prism table, which is in vacuum, with the micrometer which is outside, is sealed by a sylphon tube. (5) By connecting the micrometer head mechanically to a recording galvanometer the spectrometer may be made self‐recording. (6) The spectrometer is constructed in such a way as to give the thermopile maximum isolation from thermal fluctuations in the room.
An absorption cell is described which has the following features: (1) The cell has small windows although it will handle a beam having a numerical aperture of ⅓. (2) The radiation path in the absorbing gas is one meter. The cell may be evacuated or it will withstand pressures of several atmospheres. (4) The cell may be heated to 300°C.
Various techniques for obtaining monochromatic bands of infrared radiation are discussed. A technique is described which makes spectroscopic measurements possible with a source whose temperature may fluctuate (such as the crater of a carbon arc).
3(1932); http://dx.doi.org/10.1063/1.1748903View Description Hide Description