Volume 13, Issue 12, 01 December 1942
Index of content:
13(1942); http://dx.doi.org/10.1063/1.1714826View Description Hide Description
IN this chapter the following subjects are dealt with: (a) synthetic plastics, the plastic properties of which are of interest from the standpoint of molding and of permanence; (b) glasses, the plastic flow of which in the range from 400 to 600°C is important because this is the annealing range of glasses; (c) lead, in particular in connection with its use as sheath of high voltage cables; (d) electrical ionic conductivity of solid insulating materials in relation to their plastic flow resistance.
13(1942); http://dx.doi.org/10.1063/1.1714827View Description Hide Description
The electron microscope has been used to study two types of structures responsible for the physical colors of insects. The iridescence of the beetle Serica sericea is due to a line grating on its wing‐covers, 0.8μ between lines. The structure giving rise to the brilliant blue color of the tropical butterfly Morpho cypris is quite elaborate, consisting essentially of hundreds of vanes on each wing scale, the vanes possessing linear thickenings 0.2μ apart which reinforce the reflection of blue light. Numerous exceedingly fine markings on parts of the wing scales go down in dimensions to 60A, and some of them may be related to the chemical structure of the scales. Chemical tests show that the scales are not composed of chitin, the principal component of the external parts of most insects. It is interesting that bombardment of the scales with an intense electron beam (1000 electrons per square angstrom per second) for a matter of minutes does not appreciably affect the swelling properties of the scales in organic liquids.
13(1942); http://dx.doi.org/10.1063/1.1714828View Description Hide Description
With the increasing use of bactericidal ultraviolet lamps it has become very desirable to have more information about the accompanying production of ozone which is the only feasible agent for protecting surfaces not exposed to direct or scatteredradiation. Very little published information is available and practically all the data given in this article are new. A low pressure mercury arc lamp of the type of the Westinghouse Sterilamp gives an amount of ozone of the order of 1/100th gram per hour, corresponding to a rate of emission of energy of at least 1/100th of a watt. A gentle air motion increases the yield. All the ozone is produced within a few feet of the lamp. The rate of decomposition of the ozone after the lamps are turned off is faster the greater the surfaces compared with the volume, the higher the temperature, the higher the humidity, and the more 2537 radiation present. The most important factor, the equilibrium ozone concentration, in an enclosure of several cubic meters is proportional to the ozone produced, inversely proportional to the volume, and is reduced to about one‐third when the relative humidity changes from a few percent to near saturation and to about one‐half when the temperature is raised from 7° to 32°C. It is very roughly 25 percent lower if the 2537 radiation of the present Sterilamp, accompanying the short wave‐length ozoneradiation, is doubled.
13(1942); http://dx.doi.org/10.1063/1.1714830View Description Hide Description
For a composite filter made up of several m‐derived sections, the greatest discrimination will be obtained if the values of the design parameter m for the various parts of the filter are chosen so that successive minima of insertion loss in the attenuation band are all the same. Many different low pass structures were set up and adjusted experimentally to show this type of performance. The necessary values of m and the resulting discrimination for each network have been plotted on curves, which give information also about the sharpness of cut‐off. These curves are useful for the most economical design of low pass, or high pass, composite filters to meet definite requirements.
13(1942); http://dx.doi.org/10.1063/1.1714831View Description Hide Description
The paper gives a description of some tests carried out in preparation for the construction and development of an apparatus for artificial atomic disintegrations. The problems involved are (i) the focusing of a beam of 10–30 kv hydrogen ions from a canal‐ray ion source(glow discharge type) and (ii) the behavior of a cascade acceleration tube of the Coolidge type. In particular it was necessary to know the efficiency of the latter, i.e., the ratio of output to input currents. The general properties of electrostatic focusing systems are first treated briefly, and adequate references are given to enable those interested in the problem to pursue the matter further. It is pointed out that in view of the aberrations present, the constants of our lenses cannot be accurately calculated and we have therefore concentrated our attention on presenting the results in a concise form. Several lens systems were used to focus the canal‐ray beams and details are given in tables. It was found possible to focus at least 50 percent of the ion beam emerging from the canal into an area 1–2 cm in diameter at distances of 20–50 cm. Point foci could be obtained but the focused currents were low, i.e., spherical aberration was large. Similar performances could be obtained with a 6′ acceleration tube.
13(1942); http://dx.doi.org/10.1063/1.1714832View Description Hide Description
The relative motion of a train of n uniform cars and a locomotive is considered. If slack and rolling resistance are neglected, the system may be idealized to that of (n+1) masses connected by springs. To generalize the analysis it is assumed that identical shock absorbers of the dash‐pot or viscousfriction type are placed between the units. By considering the electrical analog of this dynamical system, its natural frequencies are determined. It is found that if the shock absorbers have a certain critical strength, no free oscillatory motion between the cars is possible. Expressions are obtained for the velocities of the several cars when the locomotive exerts an oscillatory tractive effort. By the use of the operational calculus, the response of the system when the tractive effort is impulsive is also determined.