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    LONDON. Royal Society, May 16.—Sir J. J. Thomson, president, in the chair.—A. Mallock: Note on certain coloured interference bands and the colours of tempered steel. After alluding to the interference bands seen when two rows of posts, etc., or two gratings, are viewed one through the other, the paper deals, with a particular case of such bands, namely, that when a plate of dispersive material, such as glass, is placed between the two gratings, or, which amounts to the same thing, -when a single grating is placed on a thick mirror, and the interference takes place between the grating and its reflective image. The bands so-formed are coloured. The composition of the colours in terms of primary red, green, and violet is given diagrammatically by means of Maxwell's chromatic triangle for nine examples. It is noticed that the sequence of colours in some of these agrees closely with those of tempered steel. It is shown that the colours of tempered steel are not “colours of thin plates,” and it is suggested that they must be due to the formation of some material the molecular period of which is comparable with the period of light-waves, and not to a structure comparable with the wavelength.—J. C. M. Garnett: General factors in mental measurements. An inquiry into the mathematical argument for the existence of Prof. Spearman's general factor g, in all mental abilities of which measurements had been published during many years, led to an investigation into the consequences that must follow from the condition that the correlation between every pair of columns in a correlation table is ±1. These consequences were found to be that there is one, and only one, factor common to all the qualities the correlations of which form the table; that there are no group factors common to two or more qualities but not to all; and that there may be any number of specific factors each belonging to one quality only. It was found that any quality which is distributed according to the normal law, and depends only on n independent factors (qualities), say x1x2xn, which are distributed according to the normal law and have the same standard deviation, may be represented by

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