Page:Popular Science Monthly Volume 27.djvu/584

This page has been proofread, but needs to be validated.



The Q. P. Index Annual for 1884. Bangor: Q. P. Index, Publisher. 1885. Pp. 78.

The Magnetism of Iron and Steel Ships. By T. A. Lyons. Washington: Government Printing-office. 1884. Pp. 181. Illustrated.

A Manual of the Theory and Practice of Topographical Surveying by Means of the Transit and Stadia. By J. H. Johnson, C.E. New York: John Wiley & Sons. 1885. Pp. 111. $1.25.

Commercial Organic Analysis By Alfred H. Allen, F. C. S. Vol. I. Philadelphia: P. Blakiston, Son & Co. 1885. Pp. 476. $4.50.

The French Revolution. By Hippolyte Adolphe Taine, D. C. L. Oxon. Translated by John Durand. Vol. III. New York: Henry Holt & Co. 1885. Pp. 509. $2.50.

Christian Thought. Lectures and Papers on Philosophy, Christian Evidence, Biblical Elucidation. Second Series. Edited by Charles F. Deems, LL. D. New York: Phillips & Sons. 1885. Pp. 476.

Contributions to the Knowledge of the Older Mesozoic Flora of Virginia. By William Morris Fontaine. Washington: Government Printing-Office. 1883. Pp. 143. With Fifty-four Plates.


Correction.—This year's meeting of the American Association for the Advancement of Science will begin Wednesday, August 26th; not on August 20th, as erroneously stated in the July Monthly.

Fallacies about Mines.—Mr. Albert Williams, of the United States Geological Survey, has recently exposed, in a brief monograph, some of the popular fallacies which exist, often to the detriment of miners' interests, regarding precious-metal deposits. First, are local prejudices against certain formations and in favor of others. Most of these prejudices have been contradicted in one way or another, and there is no sufficient reason that any one of the kinds of country rock prevalent in mining districts is more likely to contain metal deposits than another kind. The supposition that the richness of mineral veins usually increases with depth may or may not be justified in a particular case; the only way to find out is to examine. Miners have objections against "specimen" mines, or mines that give unusual superficial promise of richness. Here, again, the only test is by trying, and it is certainly profitable to work the mines so long as they make a paying return, while it will be time enough to stop when they cease to do so. Some miners have favorite strikes, and prefer to work in no others. They are as often wrong as right. One direction of strike may promise best in one locality, and the opposite direction in another. Another miner's fallacy is the belief that the appearance of ores is a trust-worthy index of their value. Such a belief, Mr. Williams observes, may seem self-evidently absurd to the experienced miner, but it nevertheless governs many prospectors, who hastily judge from the looks of the rock, when they should have waited for an assay. Notwithstanding the necessity exists for contradicting these fallacies, it would be unfair to infer that the whole subject of precious-metal mining is involved in doubt and perplexity. On the contrary, a great deal of solid fact is now established, room for which has been gained only by clearing away a mass of misconceptions. Much remains to be learned; in fact, the study of precious-metal deposits is only beginning. But it must be admitted that, on the purely practical side, great advances have been made.

Bark Dresses.—The tapa of the South-Sea Islanders is made from the bark of the paper mulberry-tree (Broussonetia papyrifera), and the bark clothing of the African tribes is prepared from trees of the same family. Dr. Schweinfurth describes one of these trees (Urostigma Kotschyana), which is called rokko in the country of the Niam-Niams, as standing before every hut, and as cultivated in Monbuttoland. The bark is most fit for use when the trunk is of about the thickness of a man's body. The whole stem is then peeled for a length of some four or five feet, and this without destroying the tree; for the juicy substance around the wood immediately granulates and shortly begins to form a new bark, which becomes fit for use again in about three years. Thus a tree, properly taken care of, may be made to furnish several suits of clothing during its lifetime. The rokko-bark much resembles that of the bass-wood in quality, except that the bark is not quite so thin. By partial maceration and much beating it is formed into a kind of thick and very pliant cloth. In a crude state it is grayish or yellowish, but steeped with a dye-wood it takes a brownish color like that of a common woolen cloth. It constitutes a valuable article of trade in the interior of Africa. The price varies considerably according to