portant memoir in which he endeavors to find some relation between the rotatory magnetic polarization of a substance and its refractive index, and has with this object investigated the optical properties of a great number of substances of high refracting power which have never before been examined from this point of view. It appears from the numbers given that the rotatory magnetic polarization increases with the refractive index, but much more rapidly than in a simple ratio. With respect to solutions of salts it appears that the rotation increases with the concentration, and, moreover, that anomalous rotatory dispersion is accompanied by negative magnetic rotation. In connection with this subject we may mention some observations which have been made by Mr. G. F. Fitzgerald, on the subject of Dr. Kerr's experiment. It will be remembered that at the last meeting of the British Association Dr. Kerr announced the discovery that the plane of polarization of a ray of light reflected from the polished pole of a magnet is rotated. Mr. Fitzgerald (Proc. Royal Soc., xxv. 441) offers an explanation of this remarkable fact by reference to the action of a diamagnetic transparent substance in a powerful magnetic field on a ray of plane-polarized light passing through it. The plane-polarized ray may be regarded as the resultant of two circularly-polarized rays, one right and the other left handed, the former of which has a higher refractive index for the medium than the latter, if the rotation is towards the right, and a less, if the rotation is towards the left. Applying this consideration to the case of reflection of a polarized ray from the reflecting surface of a south magnetic pole, Mr. Fitzgerald arrives at the conclusion that the reflected beam is elliptically polarized, the major axis of the ellipse making a small angle to the right of the plane of incidence. This theoretical result was confirmed by a direct experiment, and appeared also to be in harmony with Dr. Kerr's experiments. We understand that Dr. Kerr has obtained some further results in addition to those which he communicated to the British Association. We shall be glad when these are published, so that we may see their bearing on Mr. Fitzgerald's conclusions.
From The Gentleman's Magazine.
AUSTRALIAN PEARL-FISHING.
Somerset Harbor, the first Australian port of call, we entered in the midst of a tropical storm that made the little pearl-shelling vessels rock like paper boats. We remained long enough to learn something of this same pearl-fishery. One informant proved that it was a most thriving business, and deplored that, by some astonishing oversight, the Oueenslanders allow the entire profit of the enterprise to go to another colony. Nearly the whole of the boats hail from Sydney, some of whose merchants are making rapid fortunes out of the trade, upon which, added my complainant, there was no tax; not even a boat-license, he said, was imposed by the government of Queensland. The vessels engaged in the business are smart little fore-and-aft schooners, and last year there was taken from the port of Somerset not less than two hundred tons of pearl-shells, the selling price of which would be about £200 per ton. One firm in Sydney received seventy-two tons, and I heard of one Birmingham house that had already brought £30,000 worth of the material. As is the case with many other important industries by which large fortunes are made in a short time, the pearl-shelling capabilities of Queensland were discovered by accident. The hardy seamen and native divers engaged in the bêche de mer trade, about four years ago, brought up an occasional pearl oyster, and as the matter was talked about in the straits it was remembered that the blacks along the coast were in the habit of wearing crescent-shaped pearl-shell ornaments about their necks. The industry was then organized, and with the most gratifying pecuniary results. The pearl oyster averages from seven to nine inches in diameter, and the inside is lined with a beautiful coat of the mother-of-pearl from which buttons and other articles are made. At Somerset I was presented with a pair that, mounted, make capital card-trays, being fully eight inches across. The people engaged in pearl-diving seem to be a very miscellaneous set. The white men are mostly big, rough-bearded fellows, who would not thank you for inquiring too closely into their antecedents, and who adopt a remarkably "conciliating" way of dealing with their colored assistants. Very often in Australia you hear that the blacks of a certain district have been conciliated — that is to say, knocked down or shot. But it is only a very few aboriginals
