5 66 



THE POPULAR SCIENCE MONTHLY. 



The Q. P. Index Annual for 1SS4. Bangor: Q. 

 P. Index, Publisher. 1885. Pp. 78. 



The Magnetism of Iron and Steel Ships. By T. 

 A. Lyons. Washington : Government Printing- 

 office. 1834. Pp. 181. Illustrated. 



A Manual of the Theory and Practice of Topo- 

 graphical Surveying by Means of the Transit and 

 fctadia. By J. 11. Johnson, C. K New York. : John 

 "Wiley & Sons. 1885. Pp.111. $1.25. 



Commercial Organic Analysis By Alfred H. 

 Allen, V. C. S. Vol. I. Philadelphia: P. Blakis- 

 tou, Son & Co. 1885. Pp. 470. $4.50. 



The French Revolution. By Hippolyte Adolphe 

 Taine, D. C. L. Oxon. Translated by John Du- 

 rand. Vol. III. New York: Henry Holt & Co. 

 1885. Pp. 509. $2.50. 



Christian Thought. Lectures and Papers on Phi- 

 losophy, Christian Evidence, Biblical Kiucidation. 

 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-Of- 

 fice. I8b3. Pp.143. With Fil'iy-lour Piates. 



POPULAR MISCELLANY. 



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 Will- 

 iams, of the United States Geological Sur- 

 vey, has recently exposed, in a brief mono- 

 graph, some of the popular fallacies which 

 exist, often to the detriment of miners' 

 interests, regarding precious-metal depos- 

 its. First, are local prejudices against cer- 

 tain formations and in favor of others. 

 Most of these prejudices have been contra- 

 dicted 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 de- 

 posits than another kind. The supposition 

 that the richness of mineral veins usually 

 increases with depth may or may not be jus- 

 tified in a particular case ; the only way to 

 find out is to examine. Miners have objec- 

 tions against " specimen " mines, or mines 

 that give unusual superficial promise of rich- 

 ness. Here, again, the only test is by try- 

 ing, 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 fa- 

 vorite 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 be- 

 lief that the appearance of ores is a trust- 

 worthy index of their value. Such a belief, 

 Mr. Williams observes, may seem self-evi- 

 dently 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 ex- 

 ists 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 re- 

 mains 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 {Bronssonelia papyri- 

 /era), 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 rohko 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 destroy- 

 ing the tree ; for the juicy substance around 

 the wood immediately granulates and short- 

 ly begins to form a new bark, which be- 

 comes 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 pli- 

 ant 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 com- 

 mon woolen cloth. It constitutes a valuable 

 article of trade in the interior of Africa. 

 The price varies considerably according to 



