620 CURRENT TOPICS. [J, l:. I.

quartz to no quartz. This method may give a high value for quartz, but not a low one, and if none is found there is only a negligible quant i ty in the dust. This method may be modified to identify other minerals by using oils of other refractive indices, and the same limitations will hold.

R. H. ().

Human Aquarium.--( Compressed Air, Vol. 43, No. 3.1) A so- called "hum a n aquar i t .m" has recently been built in France after the plans of J. L. Breton, director of the French National Office of Research and Invention. Designed for testing submarine equip- ment, it is also to be used for giving exhibitions of divers at work, of fancy swimming under water, and of marine life of all kinds. The structure consists of a basin, approximately 4 ° feet in diameter and 15 feet deep, the upper par t of which is in the shape of a trun- cated octagonal pyramid having a base about 25 feet in diameter and sides sloping 45 degrees. The latter are made of plate glass and offer an unobstructed view of the interior of the tank from the surrounding spectators gallery, hnmediate ly beneath the pyra- midal section and built integrally with it is a pendant wall that extends down into the basin and forms an air pocket between it and the outer wall. This works on the same principle as the diving bell. As water flows into the tank and rises, the air trapped in this space is compressed, and when the air pressure and water pressure are equal the water is checked. This balance must of course be maintained; and this is done by admitt ing compressed air into the pocket as needed. Any excess air can be exhausted by way of a separate duct. The lower edge of the pendant wal~ is 4 feet 3 inches from the floor of the basin, and swimmers, or divers and other submarine workers without breathing apparatus, simply by ducking under this wall and putt ing their heads in the air pocket can fill their lungs with oxygen. The unsuspecting visitor, however, will probably wonder how the men can remain submerged as long as they do without apparent ly breathing. The water in the tank is heated for the comfort of the performers or workers and little difficulty is experienced in keeping it so because the tank is under- ground. An elaborate system of lighting has been installed. All wiring is carried in a new fireproof cable in which the dielectric is dehydrated magnesia. This remains dry throughout the life of the cable.

R. H. O.

Textile Fiber Derived from Milk. (Manufacturers Record, Vol. CVII, No. 4.) The possibility of manufacturing on a commercial