DIARY OF SOCIETIES. London. Royal Society, at«. jo.—On the Organisation of the Fossil Plants of the Coal-measures. Part XIX.: Prof. W. C. Williamson, F.R.S—On Biologic Regions and Tabulation Areas: C B. Clarke, F.R.S.—Observations on the Structure, Relations, Progressive Development, and Growth of the Electric Organ of the Skate: Prof. Ewart. Institution op Ei.scrxiCAL Engineers, at B.—Some Experimental Investigations of Alternate Currents' Alexander Siemens.—On the Specification of Insulated Conductors for Electric Lighting and other Purposes: W. H. Preece, F.R.S. (Discussion.) RoVAl- Institution, at v—Some Recent Riological Discoveries: Prof. E. Ray Lankester, F.R.S. Lostdost iNmTOTlON. at 6.—Experimental Meteorology (Illustrated): Shelford Bidwell. F.R.S. Camira Club, at 6.—Annual Meeting. At 8.—Lantern Exhibition. FRIDAY, Fmiuahtjo. Physical Society, at ;.—On Modes of Representing Electromotive Forces and Currents in Diagrams: Prof. S. P. 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