and hence the more abundant the dust the more dense the cloud. When the vapor in the second receiver was brought by circulation against the sides of the receiver, it gradually condensed on these surfaces. The density of the fog formed in common air shows what a large amount of dust is present every day in the air around us. But the particles of fog do not represent all the dust-particles in the air. If enough steam is blown into a receiver full of common air to produce a dense fog, and after the fog has settled more steam is blown in, another fog will form on the dust which still floats in the air. If this is repeated a number of times, a less dense and coarser-grained fog forms each time, till at last no fog is seen, but the condensed vapor falls as rain. These dust-particles are not the motes that we see in the path of a sunbeam; for, when common air is passed through a flame, these motes disappear, but the air still remains a good medium for fogs. It is a finer kind of dust which furnishes the fog and cloud nuclei. The products of combustion are fog producers, and especially the vapor from the burning of sulphur.
Gem Minerals of Canada.—Although, according to Mr. George F. Kunz's paper on "Precious Stones, Gems, and Decorative Stones in Canada and British North America," Canada can hardly be called a gem-producing country, it furnishes a number of stones that are of more than passing interest to the mineralogist, and of some value in jewelry and the arts. A number of gem minerals, not of gem quality, are found in examples of such size and perfection that they have been given prominent places in cabinets, and are even more prized as specimens than cut stones from other localities. Their mineralogical value gives them no small commercial importance. Of such are magnificent zircon crystals, occurring as individuals up to fifteen pounds in weight, and many finer ones weighing a pound, as well as beautiful twin crystals of the same mineral; black titanite in simple and trimmed crystals up to seventy pounds each; "vast quantities of amethyst" from Lake Superior; ouvorsovite or green chrome garnet from Orford, and white garnet crystals from near Wakefield; and apatite crystals, one weighing over five hundred pounds, of great beauty, of which the rich green variety, especially, would do to work into ornaments similar to those made from fluorite. Only a small part of the territory of the Dominion has been examined with reference to these stones; and with the discovery of new localities important additions to the list may be anticipated.
The Sliding Railway.—The Chemin de Fer Glissant, or sliding railway, at the Paris Exhibition, according to a description by Sir Douglas Galton in the British Association, is based on the two principles of causing the carriage to slide on a thin film of water introduced between the sledge-plates on which it rests; and the propulsion of the sliding train by horizontal columns of water acting through hydrants placed at intervals on the line. The system was originally designed by Girard in 1861, who made a line at his own private house, where he had an inclination of one foot in twenty. The results he obtained seemed to justify the application of the system in special cases on a paying basis. He acquired a concession in 1869 for a railway from Calais to Marseilles, to which a subvention was afterward attached. But the War of 1870 resulted in the destruction of the railway by the German army, and in the death of M. Girard in 1871. In 1885 M. Barré purchased the drawings left by M. Girard, and introduced an improvement which he considered would make the system more workable. A line on this improved system was established in the Paris Exhibition, about two hundred yards long, and trains were run upon it.
Properties of the Kola-Nut.—Kola-nuts, or the seeds of Sterculia acuminata, are allied in composition to cocoa, coffee, and tea, but contain a relatively large amount of caffeine. They are credited with strong tonic and nervous stimulant properties; with counteracting and removing the sense of exhaustion after fasting and fatigue; with having antagonistic reaction to alcohol; and with a purifying influence on water. Their value as a therapeutic and dietetic agent has been tested by Surgeon R. H. Firth, who concludes that kola is not a food; that it increases total urinary water, has a stimulant action on the nervous system, temporarily strengthens the
