A survey is given of recent work on the action of light on bromine vapour, both dry and in presence of air and moisture.

Suggested explanations of the facts are discussed. It is concluded that the influence of water is due to a “poisoning” of the walls of the vessel, which prevents them from catalysing the recombination of bromine atoms.

The subject of this chapter, unlike Jacobians and Hessians, increases without halt in popularity, the number of relevant writings coming up for report in the new period being a half more than in the period immediately preceding, where the rate of increase had been still higher. A notable feature, too, is the exceptional attention given to Pfaffians, and along with it the growing tendency to view them as entities apart from determinants. Of less importance perhaps but interesting is the first appearance (in 1894) of determinants that are “block” skew.

The three Huygens lenses in the possession of the Royal Society of London are the most remarkable long-focus lenses that were produced at that epoch; they are described in the Record of the Royal Society (1912) as follows:—

3. Huygens's Aerial Telescope.

(1) An object-glass of 122 feet focal length, with an eye-glass of 6 inches, and original apparatus for adjustment, made by Huygens, and presented by him to the Royal Society in 1691.

(2) The apparatus for using Huygens's object-glass, constructed by Hooke.

(3) Additional apparatus, by Dr. Pound. Presented by Dr. Bradley.

(4) Ditto, by Mr. Cavendish.

4. An object-glass by Huygens, of 170 feet focal length. Presented to the Royal Society by Sir Isaac Newton, P.R.S.

5. An object-glass by Huygens, with two eye-glasses by Scarlet, for a telescope of 210 feet. Presented by the Rev. Gilbert Burnet, M.A., F.R.S., in 1724.

1. Salts of 5:6-benz-4-carboline and its derivatives precipitate colloidal gum benzoin and other negatively charged lyophobic sols at comparatively low concentrations, but at considerably higher concentrations they do not bring about flocculation of these colloids but confer a positive charge on the colloidal particles. These effects are similar to those observed with many dyestuffs.

2. The effect of the simultaneous presence of benzcarboline salts and of gelatin of pH 4·6 and pH 7·0 has been examined. The presence of small quantities of gelatin appears markedly to decrease the adsorption of benzcarboline ions.

3. The effect of various benzcarboline salts on the electro-capillary curve of mercury has been determined. In presence of small concentrations (M/20000) of these salts the maximum of the electro-capillary curve occurs to the right of that of the primitive (negative polarisation of the mercury), and the greatest fall in surface tension occurs to the left of the maximum of the primitive (positive polarisation of the mercury).

4. These results indicate high adsorption of benzcarboline ions even on a positively charged surface. The possible cause of this unexpected result is discussed.

The authors wish to express their indebtedness for a grant from Imperial Chemical Industries, Ltd., which defrayed in part the cost of the apparatus employed in the electro-capillary experiments. They also wish to express their thanks to Mr W. Leeper and Mr W. Spragg for valuable assistance.

1. The plumage of the Brown Leghorn fowl is analysed and the extent of its dependence on the activity of the thyroid and gonad is discussed.

2. Hypothyroidism results (a) in a diminution in the amount of melanin and a coincident increase in the red pigment; (b) in an increase in the amount of fringing due to a lack of barbule formation. The female pattern tends to disappear.

3. Hyperthyroidism in the male gives exactly the opposite effect—i.e. the melanin increases in amount while the red pigment and fringing tend to disappear. In the female the effect of hyperthyroidism is slight, and with moderate doses of thyroid there is practically no modification of the female pattern of pencilling and no melanin appears in the breast. The neck hackle, however, becomes darker and shows a decrease in fringing.

4. From these results, together with what is known concerning the effect of gonad on plumage, a hypothesis is advanced, that whereas the plumage typical of the male is developed independently of the gonad and depends for its maintenance on a certain level of thyroid functioning, both gonad and thyroid play a part in regard to that of the female; the former stimulates the latter to a higher level of activity than that present in the male and so indirectly causes a hyperthyroid effect on the feathers. At the same time it modifies this condition by acting directly on the feathers and restricting the deposition of melanin.

5. The fact that in both sexes the plumage in the young chick is similar to that of the female puts this theory in question. There is evidence to show, however, that yolk may have a modifying effect on plumage similar to that of the ovary, and thus the doubt regarding the validity of the hypothesis can be removed by the suggestion that the chick plumage develops under the influence of the yolk in its own yolk sac. This second theory gains confirmation by a study of the atypical plumage which is occasionally met with in growing females, and also by a consideration of the type of plumage developed in juvenile females following the successful implantation of testis.