When aluminum was used against iron in atmospheres of air and hydrogen, a rectification of 20 per cent was again observed. When hydrogen was used, the rectification was just perceptibly less than in air.

7. Placing a metallic band about one electrode and connecting this band with the other electrode, a strong, often complete, rectification is produced, the current passing toward the electrode having an external band. It has frequently been noticed that placing the hand near a discharge tube steadies the discharge. An earthed metallic band about the tube near one electrode was much more effective in strengthening

the discharge. Finally, this band was connected with the opposite electrode and complete rectification obtained. A similar device has been used to facilitate starting in mercury vapor lamps, a metallic covering being placed about the cathode and connected to the anode.

Throwing an intense beam of sunlight on the front face of one of the (disk) electrodes by means of a lens produced no perceptible rectification. The effect of exposing one electrode or the adjacent gas to the action of X rays was not tested, but from (4) and (6) we should expect the side exposed to become anode.

Tests 8 and 9 were made with tubes provided with three mercury electrodes. One of these was connected to one 2,000-volt terminal, and the other two, through different resistances, to the other. Current was found to enter through the low resistance and leave by the high. Such an effect by (3) would be produced by the low-resistance electrode being more heated by the greater current. When connections were made with equal resistance and one electrode heated the current passed from hot to cold in accordance with (3) and (4).

We may get a better idea of what actually occurs in the process of partial rectification from the accompanying figure (fig. 2). Let the curve () be the characteristic gas-conduction curve for the tube used-i. e., the fall of potential between electrodes as a function of the current. Impress the alternating voltage E (1) on the tube having such an external (ohmic) resistance in circuit that the line E-i R will have the slope indicated, then i (t), here plotted directly, will represent the form of the corresponding curve of current through the tube as a function of time. Anyone who has ever plotted these current curves knows how entirely their form changes with even a slight change in the form of the gas curve & (), and these & (2) curves change in form greatly as conditions in the tube are varied. For instance, at very low pressures the () curve is elevated and flattened. At high pressures it may rise continually, particularly if the electrodes be small or pointed. If the tube be illuminated by X rays the maximum of the ε (i) curve will be sharpened, lowered, and displaced toward the left. If then the electrodes are under different conditions, the (¿) curve will vary in form with the direction of the current through the tube, and therefore the current curves i (t) will no longer be symmetrical about the horizontal axis. The reversed (lower) part of the curve will be more flattened or rounded say than the upper, and the effect will be shown as partial rectification.

A tube having one internal and one external electrode showed no trace of rectification. This might have been expected, since in this case the (i) curve rises steeply and continuously and the current curve i(t) is a low, broad sine curve which would show little, if any, dissymmetry.

ON FIBERS RESEMBLING FUSED QUARTZ IN THEIR

ELASTIC PROPERTIES.

By K. E. GUTHE.

The advantages of quartz fibers as suspensions, principally their small elastic fatigue, great strength, and the possibility of drawing very fine threads, have led to their use in a great many important investigations where fine suspensions and a steady zero point are required.

In my work, suspensions were needed, able to carry a load of 500 grams and more and at the same time having as small an elastic fatigue as possible. Naturally fused quartz was selected as the substance promising the best results. Such fibers must be rather thick, from 0.1 to 0.2 mm in diameter. Since it was desired to draw them at least 1 meter in length, it required the melting of a rather large bead free from air bubbles. The process of building up quartz rods is known to be rather tedious. Shenstone's method" is simpler, and consists of heating the crystals to about 1,000° C. and suddenly quenching them in cold water. The crystals after such treatment are not shattered, and do not break when brought into the oxy-hydrogen flame. A stick of the proper dimensions is easily formed, containing, however, a large number of air bubbles. To remove these is a very tedious task and particularly exasperating, because quartz at the high temperature of the blowpipe flame is quite volatile, about one-half of the mass evaporating during the process.

Whichever method is employed it means a considerable loss of time, if a great many fibers of the dimensions necessary for this work have to be drawn.

Boys, in his first paper on this subject,' mentions his experiments on a great many minerals, of which only a few, however, could be drawn into fibers, and these he says were far inferior to those made from

a Shenstone: Nature, 64, p. 65; 1901.
Boys: Phil. Mag., 23, p. 489; 1887.

fused quartz. I have also tried a great number of substances, all silicates of magnesium: Enstatite, Olivine, Serpentine, and Meerschaum, without success. Only the Amphibol-Asbestos, Mg,CaSi,O,2, in the ordinary mineral form, as well as when specially prepared for chemical purposes, and the Steatite or Soapstone, Mg,H,Si,O,,, give clear beads before the oxy-hydrogen blowpipe. These, under proper precautions, can be drawn easily to fibers of the desired dimensions. The soapstone is especially easily worked and gives fibers of practically the same elastic properties as those of quartz. Since the method of making them is so simple and requires little time, a short description may be of general interest. The soapstone when heated to a high temperature becomes exceedingly hard, and is used commercially under the name of “lava" for making apparatus intended to be able to stand high temperatures-for example, tips of gas-burners. While it can not be melted before an ordinary blowpipe, it does so before an illuminating gas-oxygen jet and forms a clear bead, usually of a greenish tint, due to the presence of a trace of iron. The original soapstone or the "lava" will do equally well, the most convenient form being small cylindrical sticks. (I obtained such cylinders 3 mm in diameter and 7 cm long, giving colorless transparent beads about 5 mm in diameter, from the Chattanooga Sunlight Lava Manufacturing Company.) If the flame of the blowpipe is too long or the mixture of the gases not well adjusted, the substance will boil violently, while with a small, quiet flame it melts without boiling, a slight development of gases being noticeable only at the upper, cooler part of the bead. After taking the pearl out of the flame the thread is drawn, its thickness depending upon the temperature and rapidity with which it is drawn. Very fine fibers can thus be secured. The fibers should not be heated after being drawn. In a Bunsen burner, for instance, they will immediately become white and break to pieces.

Elastic fatigue. It is very well known that fine quartz fibers show hardly any elastic fatigue," but with thicker fibers of 0.1 to 0.2 mm diameter the effect of elastic fatigue became quite apparent. Careful experiments showed that small twists, or twists of small amplitude, do not affect the zero point, while larger twists, being continued for sev eral minutes, would displace the zero point. The apparatus used allowed a turning of the torsion head, while the lower end of the fiber was held in its original position. After release the zero could be redetermined in a few seconds and the slow disappearance of the effect of elastic fatigue observed. With fibers 70 cm long and 0.1 mm diameter

a Boys: Phil. Mag., 23, p. 496, 1887; Threlfall: Phil. Mag., 30, p. 113; 1890.

the displacement, after release from a torsion of 360° lasting five minutes, amounted to as much as 2 in 3,000. Fibers made of steatite showed about the same effect, which is, however, very much smaller than any other substance experimented with, and about one-half to one-third of that shown by steel or phosphor bronze.

For these experiments the quartz and steatite fibers had been silvered at their ends, then coppered, and finally soldered into large brass pins clamped securely in the supports. Thus the elastic fatigue observed can not be attributed to an effect of the material with which fibers were fastened to the other parts of the instrument.

Tensile strength.-The tensile strength of very thin quartz fibers is quite large, 10×10° dynes per cm2, but it decreases appreciably with increasing thickness." My experiments show the same results. From the following table it is seen that the tensile strength of the steatite fibers is at least as large as that of quartz. For comparison the values given by Boys (B) are added. The decrease of tensile strength for the thicker fibers is very striking. For the thickest fibers it is, however, still as large as that of brass.

For thick rods the tensile strength is considerably smaller, as shown recently by Schulze," who found a value of 0.6×10° dynes/cm2 for a rod having a cross section of 0.272 cm3.

a Boys: Phil. Mag., 30, p. 116; 1890.

Schulze: Ann. d. Phys., 14, p. 384; 1904.