POPULAR MISCELLANY. 



S7Z 



noticed with the nalied eye. When the mir- 

 ror is cast, the cooling process has the effect 

 of drawing it slightly out of shape, and the 

 impress of the ornamentation on the back of 

 the disk gives a practically indistinguishable 

 variation in convexity on the smooth sur- 

 face that is only noticed when the reflection 

 is cast upon a screen. The mirrors are not 

 made for the " magic " purpose. They are 

 ordinary mirrors, whose magic properties 

 are the result of chance, and not more than 

 one in a thousand possesses them. The 

 author conceives an application of the prin- 

 ciple of these mirrors to the realization of 

 the idea of seeing by telegraph, and suggests 

 that, by the use of electro-magnets and 

 selenium, a metal peculiarly sensitive to 

 light-rays, it might be possible to transfer 

 over hundreds or thousands of miles the 

 reflection of letters, or even faces. 



Effects of Tile-Braining.— The influence 

 of tile-draining in flood and drought was 

 thus presented by Prof. R. C. Kedzie, in a 

 paper read at the American Association: 

 " 1. Surface ditching in conjunction with 

 deforesting may increase floods and contrib- 

 ute to droughts. 2. Tile-draining may in- 

 crease floods at the " break-up " in the 

 spring, where the waters accumulated in the 

 surface-soil by joint action of frost and soil 

 capillarity during the winter and surface 

 accumulation in form of snow are suddenly 

 set free by a rapid thaw. 3. During the 

 warm months tile-draining tends to mitigate 

 floods by taking up the excessive rainfall 

 and holding it in capillary form, keeping 

 back the sudden flow that would pass over 

 the surface of the soil if not absorbed by it 

 and escape by flood ; and also in mitigating 

 summer drought by increasing the capacity 

 of the soil to hold water in capillary form 

 and draw upon the subsoil water-supply 

 by reason of the increasing capillary power 

 of such soil produced by tile-draining." 



International Congress of Hydrology and 

 Climatology. — The second triennial session 

 of the International Congress of Hydrology 

 and Climatology is to be held in Paris near 

 the beginning of October, 1889. The Presi- 

 dent of the Committee on Organization is M. 

 E. Renou, director of the Meteorological Ob- 

 servatory of the Pare de Saint-Maur. The 



committee has already arranged that the fol- 

 lowing questions, among others, shall be dis- 

 cussed : Conditions to be observed in the 

 installation of a meteorological observatory ; 

 rules for weather-forecasting, and organiza- 

 tion of weather-announcements at sanitary 

 stations ; climatology of different sanitary sta- 

 tions ; comparison and classification of sani- 

 tary stations from the point of view of their 

 climatological conditions ; on the action of al- 

 titude and climates m affections of the lungs ; 

 programme of a course of instruction in cli- 

 matology. Communications should be ad- 

 dressed to the secretary-general, M. Dr. de 

 Rausc, Paris, 53 Avenue Montaigne, from 

 the 1st of October to the 1st of June, and at 

 Neris (AlHcr), from the 1st of June to the 

 1st of October. 



Mineral Evolution.— Dr. T. Sterry Hunt 

 has asserted that " the transformation of 

 the primitive igneous material of this earth's 

 crust through the action of air and water, 

 aided by internal heat, presents a mineralogi- 

 cal evolution not less regular, constant, and 

 definite in its results than the evolution ap- 

 parent in the organic kingdoms." Continu- 

 ing the discussion of this subject in the Brit- 

 ish Association, he shows that the stability 

 of silicated species under atmospheric influ- 

 ence is very variable, some being readily de- 

 composed, and others very permanent ; the 

 indifference or chemical resistance, more- 

 over, increasing with the hardness or me- 

 chanical resistance. "These two qualities 

 vary for species of analogous constitution 

 directly as their condensation ; while, for 

 species of similar condensation and hard- 

 ness, the chemical indifference increases as 

 alumina takes the place of the ordinary pro- 

 toxide base, lime, magnesia, ferrous oxide, 

 and alkalies — a fact readily explained by 

 the comparative insolubility of alumina and 

 aluminous silicates in atmospheric waters." 

 Other changes less well known take place 

 in silicates by the subterranean action of 

 watery solutions, when a greater insolubility 

 determines the formation of certain softer 

 hydrated magnesian and aluminous species 

 by epigencsis from harder and more con- 

 densed species, Mr. E. A. Ridsdale has 

 spoken of the production and conservation 

 of more stable species as described by Dr. 

 Hunt as a gradual " selection of inert forms," 



