It is worthy of remark that in general, even with oil drops, almost all of those behaving abnormally fall too slowly, that is, they fall below the line of Fig. 5 and only rarely does one fall above it. This is because the dust particles which one is likely to observe, that is, those which remain long in suspension in the air, are either in general lighter than oil or else expose more surface and hence act as though they were lighter. When one works with particles made of dense metals this behavior will be still more marked, since all surface impurities of whatever sort will diminish the density. The possibility, however, of freeing oil-drop experiments from all such sources of error is shown by the fact that although during the year 1915-16 I studied [Pg 166] altogether as many as three hundred drops, there was not one which did not fall within less than 1 per cent of the line of Fig. 5. It will be shown, too, in this chapter, that in spite of the failure of the Vienna experimenters, it is possible under suitable conditions to obtain mercury drops which behave, even as to law of fall, in practically all cases with perfect consistency and normality. When E. Weiss in Prag and K. Przibram in the Vienna laboratory itself, as explained in chap. VII, had found that for all the substances which they worked with, including silver particles like those used by Ehrenhaft, gave about the right value of , although yielding much too low values of when the latter was computed from the law of fall of silver particles, the scientific world practically universally accepted our explanation of Ehrenhaft’s results and ceased to concern itself with the idea of a sub-electron.[113] In 1914 and 1915, however, Professor Ehrenhaft[114] and two of his pupils, F. Zerner[115] and D. Konstantinowsky,[116] published new evidence for the existence of such a sub-electron and the first of these authors has kept up some discussion of the matter up to the present. These experimenters make three contentions. The first is essentially that they have now determined for their particles by equation (29); and although in many instances it comes out as in electrolysis, in some instances it comes out from 20 per cent to 50 [Pg 167] per cent too low, while in a few cases it is as low as one-fourth or one-fifth of the electrolytic value. Their procedure is in general to publish, not the value of , but, instead, the value of obtained from by inserting Perrin’s value of () in (29) and then solving for . This is their method of determining “from the Brownian movements.”