Volume 12, Issue 2, 01 February 1941
Index of content:
12(1941); http://dx.doi.org/10.1063/1.1712881View Description Hide Description
The optical properties of rubber are discussed under four main headings: absorption,scattering,refractive index, and double refraction. A general survey of the results of previous work in each of these fields is given. Some of the possibilities for future investigation are indicated. New experimental data are presented for the transmission values of milled pale crepe and a soft vulcanized rubber compound at wave‐lengths from 400 to 750 mμ. The results of some measurements on scattering are also included. The variation of refractive index with wave‐length is given, as calculated from unpublished measurements of the angles of minimum deviation of prisms of unvulcanized and of vulcanized rubber.
12(1941); http://dx.doi.org/10.1063/1.1712883View Description Hide Description
An account is given of further work on capillary ion sources of the diffusion type. Both metal and glass capillaries have been investigated. The performance of the metal sources is affected by surface conditions which are difficult to control. The average proton yield from these sources is about ten percent. It was found that the yield could be increased to about fifty percent by coating the surface with phosphorus pentoxide. Sources constructed of Pyrex have a proton yield of about sixty percent and also greater stability in operation, as well as certain other advantages. Various characteristics of the output of both types of source are described as functions of the source geometry, arc current, and other variables.
12(1941); http://dx.doi.org/10.1063/1.1712884View Description Hide Description
An experimental investigation has been made of the initial focusing of ions from capillary sources of the diffusion type described in the previous paper. The lens system used consisted of a 90‐degree cone at the ion source followed by three coaxial cylinders which were arranged at various potentials up to 25 kilovolts. Since the beams are rendered slightly luminous by traces of gas in the high vacuum region, they have been studied by a photographic method. The beams have also been studied by an electrical scanning method. Both types of investigation were made as functions of the electrode potentials and arc variables and are in good agreement. Based on these observations a focusing and canal arrangement suitable for differential pumping has been tested. This arrangement has been embodied in a design for a projected ion gun assembly.
12(1941); http://dx.doi.org/10.1063/1.1712885View Description Hide Description
When an oxide‐coated cathode tube of the gas or vapor type passes more than a certain amount of current a spark or cathode spot occurs on the cathode and the tube is damaged. A peak current rating is, therefore, essential for any tube of that type and it becomes necessary to take data on how the sparking current is influenced by cathode temperature, vapor or gas pressure and other factors. By ordinary test methods each spark is so destructive that only one reading can be taken on one tube and the effect of the above factors is confused by the variation in quality of tubes used to obtain the data. The authors have developed a test procedure that so limits the duration of the spark that very little damage to the cathode results. This makes it possible to obtain a large number of readings on each tube and thereby observe effects otherwise obscured. The experimental procedure appears to be a good one for investigations in this field and the results obtained shed some light on the mechanism of sparking.
12(1941); http://dx.doi.org/10.1063/1.1712886View Description Hide Description
The settlement of soils under load is caused by a phenomenon called consolidation, whose mechanism is known to be in many cases identical with the process of squeezing water out of an elasticporous medium. The mathematical physical consequences of this viewpoint are established in the present paper. The number of physical constants necessary to determine the properties of the soil is derived along with the general equations for the prediction of settlements and stresses in three‐dimensional problems. Simple applications are treated as examples. The operational calculus is shown to be a powerful method of solution of consolidation problems.
12(1941); http://dx.doi.org/10.1063/1.1712887View Description Hide Description
It has been found possible to draw currents of the order of several thousand amperes from cold metals by field emission in vacuum. This principle has been put to use in the design of a condenser discharge x‐ray tube for high speed radiography. An auxiliary electrode spaced close to the cathode and connected to the anode through a high resistance serves to initiate the discharge which is then transferred to the anode. This auxiliary electrode is made in the form of a focusing electrode.Radiographs of bullets and the internal workings of other high speed objects are now made possible.