4000 \(\dfrac{\mathrm{cm}^3}{\mathrm{sec}}\) for air1). The enormous advantage of Langmuir’s pump in comparison with all the others is the circumstance that, as the pressure decreases, the pumping speed must remain constant, whereas for all Gaede pumps the speed falls sharply as the vacuum increases. With the comparatively great speed possessed by the molecular pump, it is of little use because of the extreme difficulty of giving it the quiet position necessary for a tight connection with the space being evacuated. For hydrogen, the maximum pumping speed of condensation pumps reaches up to 7000 \(\dfrac{\mathrm{cm}^3}{\mathrm{sec}}\).

3) Coolidge’s metal tube (see Fig. 4) consists of a copper tube \(a\), into the front part of which is soldered a platinum mirror \(g\), serving as the anticathode. The anode of the tube is the spiral \(f\), located inside a cylinder drilled into the inner

Fig. 4.

copper tube \(e\). The insulator is the glass \(c\), connected with the copper tube \(a\) by the platinum plate \(b\); \(h\) are wires supplying current to the spiral \(f\). Such a tube, when the outer tube \(a\) is cooled, withstands a load of 200 milliamperes. Its advantages are the following:

1) Small dimensions: length about 30 cm, width in the region of the anticathode 2 cm (in the drawing the length is about \(\dfrac{1}{3}\) of the real one, and the width about half the actual one). Weight \(\dfrac{1}{2}\) English pound. 2) Narrowness of the beam of rays issuing from the tube, or absence of lateral rays.

N. Selyakov.

A New Study on Triboelectricity

P. E. Shaw. Experiments on tribo-electricity (Proc. Roy. Soc., November, 1917)2.

The study of electricity, as is known, began together with the first triboelectric experiments, or experiments on the excitation of electrification by means of friction (Thales, about 580 B.C.; Gilbert, 1600; Guericke, 1663). It is therefore all the more surprising that at the present time, when

electricity has grown into an extensive science, which has separated out from itself several disciplines that are, to a certain degree, independent; the section on triboelectricity is in neglect, it is scarcely studied; the amount of information concerning it has hardly increased over the last hundred years (even in extensive courses of physics this information is usually accommodated on a few pages); the most fundamental questions of a theoretical nature concerning this area remain unresolved.

In the Proceedings of the Royal Society of London for November 1917, Shaw sets forth the results of his investigations on triboelectricity. Shaw gives a triboelectric series of 36 members1; moreover, the chief essence of his work consists in the fact that the members of the series were subjected by him to systematic investigation with respect to changes in surface conditions by various methods: by raising the temperature to the point of heating and during it, by scraping, by polishing, and so on.

It turned out that a change in the state of the surface of a given substance has an extraordinarily strong influence on the place occupied by this substance in the series. Ordinary soda glass stands in 5th place if its surface is polished; but it moves to 21st place if its surface is made matte, and to 26th place if its temperature is raised to \(245^\circ\). Mica, normally occupying 6th place, passes to 18th when its surface is made matte, and to 26th when it is heated to \(270^\circ\). Here we have examples of substances which under ordinary conditions are preferentially charged with positive electricity, but after the indicated change in their surface conditions acquire, on the contrary, a tendency to be charged with negative electricity. Ebonite, conversely, when its surface is made matte, passes from 28th place to 27th; when heated to \(100^\circ\), it is already in 21st place. All the changes occurring in this way obey, as Shaw indicates, the following simple rule: every substance standing above the 14th place of the series moves downward if it is heated or if it is given a matte surface; while every substance standing below the 14th place, under the same conditions, strives to move to a higher place. Thus, substances standing at the ends of the series, as a result of the indicated changes of state, reveal a tendency toward convergence (from this it follows that the difference in electrical states obtained by them upon friction decreases). The temperature at which displacement occurs as a result of heating is a quantity quite definite for the given material; it was determined for sixteen substances and was found to lie within the limits from \(70^\circ\) to \(300^\circ\).

A. Bachinsky.

1. The triboelectric series consists of substances arranged in such an order that each substance, when rubbed with any subsequent substance, becomes positively electrified. Such a series was first constructed by Young in 1807. We give here several members of the triboelectric series given by Faraday:

   \[ \begin{gathered} +\\ \text{Cat’s fur}\\ \text{Flannel}\\ \text{Ivory}\\ \text{Rock crystal}\\ \text{Cotton paper}\\ \text{Metals}\\ \text{Sulfur}\\ - \end{gathered} \] ↩↩

2. Abstract in Nature, No. 2512, Dec. 20, 1917. ↩