An Attempt to Detect a Change in the Heat Conductivity of a Selenium Crystal with a Change in the Illumination

Modern electron theories indicate that the electrical and thermal conductivities of good conductors should stand in very close agreement with each other. One of the first theoretical developments was that of Drude. While perhaps, it will not be necessary to rewrite his formula here, we can at least state that he determined on purely theoretical grounds that the ratio of the thermal to the electrical conductivities for good conductors should he a function only of the absolute temperature. This theoretical formula has had excellent verification in the work of Jaeger and Disselhorst, who worked with most of the common metals. It occurred to the writer that an interesting experiment could be performed with an isolated crystal of selenium in order to determine whether or not the action of light lowers its resistance to heat conduction in the same or any other measure that it does in the case of the electrical resistance

The Effect of Drawing on the Crystal Structure of Tungsten Wires

The writer has in various places published results of tests on the coefficient of rigidity of drawn tungsten wires. The latest results indicated clearly that in a series of wires drawn down from the same original stock the coefficient of simple rigidity progressively increased as the diameters of the wires decreased. For example, the value of n ranged in the case of two extremes of five such wires from 14.15xl011 to 15.10x1011 dynes per square cm., for corresponding radii of 0.0227 cm., and 0.00240 cm. The hypothesis was put forth at that time that a change in the crystal structure which was limited to the surface, and which yielded a greater rigidity for the wire would account for the results. This, because as the wires become progressively smaller the effect of the surface would become more and more pronounced

The Photographic Determination of the Form of an Airplane Loop, and the Dynamics of the Loop

During a greater part of the years 1918 and 1919, the writer was engaged at Langley Field, Virginia, on experimental work connected with the determination of bomb trajectories. The work was under the direction of Dr. A. Wilmer Duff, as Engineer-in-charge, and the writer as assistant engineer. The credit for the development of the photographic method, described below, is due to Doctor Duff. The details connected with this paper, have been worked out by the writer as an interesting and important side issue of the main problem

On the Variation in the Reflecting Power of Isolated Crystals of Selenium and of Tellurium with a Variation in the Azimuth of the Incident Plane Polarized Light

The reflecting power of a surface is defined as the ratio of the intensity of the light reflected at perpendicular incidence to the intensity of the incident light. There are two ways of determining the reflecting power of a metallic surface. One is by a direct, or photometric (dioptric) method. The other is by an indirect (katoptric) method

Some Recent Discoveries Concerning the Behavior of Platinum-Iridium Wires

The remarkable elastic properties of a certain platinum-iridium wire containing 40 per cent of iridium were first announced by Guthe. In his experiments the wire was used as the suspension of a torsion pendulum. Although the amplitudes of vibration were less than 50 degrees, a marked increase both in the period and in the logarithmic decrement accompanied the increase in the amplitude. Cylinders of equal mass but of different moments of inertia were suspended from the wire, set in vibration, and timed, but as a result of these experiments no change was observed in the logarithmic decrement-amplitude curves. This absence of any effect led to the supposition that the damping was proportional to the amplitude, and independent of the velocity

A Note on Kater\u27s Reversible Pendulum

In one of our laboratory classes recently, in connection with a routine experiment with Kater\u27s pendulum, certain of the students were confronted with the situation in which, although the periods of vibration from each of the two knife edges were practically identical, the distance between the knife edges was by no means equal to the length of the equivalent simple pendulum. None of the treatises on dynamics available offered any help in their difficulty. In all the discussions it was virtually stated that when the periods from the two knife edges were equal the distance between knife edges was equal to the length of the simple pendulum of equal period

A Redetermination of the Principle Reflecting Powers of Isolated Selenium Crystals

Some time ago, following the publication of a paper by one of my former students, Mr. C. H. Skinner, I attempted to check his results by direct experiment. The paper referred to dealt with the optical constants of isolated selenium crystals. Of these constants, the reflecting power is the only one that offers itself to an easy experimental test. It must be said that the results obtained by Skinner were obtained by indirect means, and since the equations used in reducing his results to optical constants were somewhat complicated, and rested on foundations none too sure, it was important for our own satisfaction at least, to make a direct test of their accuracy

On the Recovery of the Elastic Properties of a Platinum Iridium Wire

The writer has at various times discussed the elastic properties of wires made by alloying different percentages of iridium with platinum. In particular this study has been carried on with a 40 per cent alloy. The principal feature of the previous work was a study of the torsional elastic properties of this wire; the wire in these cases being used as the suspension of various torsion pendulums. One of the facts of most importance developed in this investigation was that the period of the pendulum not only depended upon the amplitude (a fact discovered by Guthe) but that the relation of the period to the amplitude was not always a constant one. In fact in the earlier investigation it appeared that the connection between period and amplitude was such a complicated one, that any further study of the elastic properties must first be directed toward this one relation of period and amplitude. A good advance in this knowledge was recorded in the paper previously referred to, but much remains to be done. Its importance in the theory of elasticity can hardly be overestimated

The Intrinsic Intensity and Percent of Polarization of Light Transmitted through Deep Slits

It is assumed that the light incident upon the first opening of a slit between various metals is diffracted in the usual manner, and finally emerges from the far end of the slit after repeated reflections. The reflecting coefficients of the various metals considered are calculated for the proper angles of incidence from a knowledge of the index of refraction of the metal, and from its coefficient of absorption. In view of the fact that the coefficients of reflections for light possessing an electric vector perpendicular are much larger than for light with the electric vector parallel to the plane of incidence, there will be partial polarization of the emergent light

Notes on Certain Elastic Peculiarities of Phosphor Bronze Wires

Some previous work by one of the authors with wires of an alloy of platinum-iridium, portions of which work were published in these Proceedings, indicated that when the wires were used as suspensions for torsion pendulums, the relations between the period of vibration and the amplitude were exceedingly complicated. The effect of drawing these wires was dealt with in another paper. In all these papers referred to, the statement was made that similar tests should be applied to some of the more common wires in the hope of finding similar, even though smaller effects. Through press of work these experiments have been deferred until the present year. This particular paper will deal with but one feature of the work, namely, the effect of drawing on the elastic nature of phosphor bronze wires. The writers are indebted to the American Electrical Works, of Phillipsdale, Rhode Island, for kindly furnishing them with specimens of the wires