Popular Science Monthly/Volume 41/May 1892/Notes
Involuntary Movements. — The article on Involuntary Movements, by Prof. Jastrow, published in the April number, will appear in a more extended form in the forthcoming issue of the American Journal of Psychology.
A promising account is given of the copper mines of French Congo. They lie in the district around the source of the Ludima-Niadi, about two days south of Stéphanieville. The ore, a malachite, is brought to the surface by about three hundred and fifty negroes, whose methods of work are extremely simple. They reach the mineral by digging out, with implements of hard wood, holes or shafts three feet wide and twice as deep. The malachite is broken on the ground, and afterward when pulverized is put into a furnace on a tray with charcoal, on which bellows are made to play. In due time the tray is removed by means of pieces of bamboo and the metal is poured into sand molds. The entire district is said to be rich in copper, and masses of malachite are frequently found in the Ludima.
It has been shown by Mr. Aitken that the presence of dust, affording a free surface on which vapor may condense, is essential to the production of fog. The specific action of the dust varies considerably according to its composition and to the size and abundance of the particles present. Sulphur burned in the air is an active fog-producer; so are salt and hygroscopic bodies generally. Non-hygroscopic bodies also produce it, especially if they are good radiators of heat. The exceedingly minute amount of matter capable of inducing fog is a noticeable feature in the investigation. The condensation of moisture upon dust offers an effective process for removing all kinds of impurities from the air, for the floaticles are weighted by the moisture settling upon them.