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In this paper experiments are described showing that the value of the coefficient of static friction decreases as the number of successive small relative displacements of a spherical slider on a flat metal base increases. It is shown that the results can be attributed to wear of the slider. The effect seems to become distinctly noticeable only in the case of sliders which are nearly perfectly spherical.

Summary The Ramanspectrum of transformer oils has been investigated both before and after oxidation of the oils. A change in the intensity of the C-H oscillation lines could be shown. The photochemical chlorination of chloroform was followed completely by means of the Ramaneffect, the intensity of the CCI, lines providing an accurate method of estimating the amount of CCI, present. The calibration curve required for this purpose, which gave the relation between the amount of CCI, present in a mixture of CCI, and CHCI 3 and the corresponding intensities of the CCI,, Raman-lines, proved to be a straight line. From this fact the incoherence of the Raman-radiation was inferred. A new way of illuminating a photochemical system has been worked out. Experimental measurements and mathematical calculations concerning the light absorption in such a system are in perfect agreement with one another. The advantages of this “source of light” are summarized. Very simple, but accurate experiments with a selenium photocell confirmed the results obtained with the Ramaneffect. A theoretical interpretation of the empirical reaction equation is given,while the work of S c h u m a c h e r and W o I f f allowed an interesting comparison to be made between the reaction in the liquid- and the gaseous phase. It is maintained that highly unstable chain products can be detected by means of the Ramaneffect.

A “Selenium Photo Element” was exposed to a beam of monochromatic light of weak intensity, the photo electric current being about 2 × 10−9 Amp. Under these conditions the element was observed to be very slow, the velocity of indication being dependent on the wavelength as well as on the surface intensity of the incident light. These properties make the photo element especially unsuitable for the measurement, of such weak intensities as were used in the experiments.