CONTENDS: 
Page 
Art, XXIX.—Recent Progress in Optics; by W. LeContE ~ 
STHVENG she cwe.s Ls. 15-7 b eae ee ee 277 
XXX.—Quantitative Deteriaination of Perchlorates; by D. 
Aree Oe ee ON ann A ; 
XXXI.—Occurrence of Copper in Western Idaho; by R. L. 
PACKARD feet G25 os 33 ha Beek ee 298 
XXXII—Demonstration of Caustics; by R. W. Woop --.. 301 
XXXIII.—Spectrum of Helium; by W. Crooxus.--.----- 302 
XXXIV.—Igneous Rocks of the Sweet Grass Hills, Mon- 
tana; by W. H. Weep and L. V. Pirsson..-._--_- 309 
XXXV.—Distribution and Secular Variation of Terrestrial 
Magnetism, No. III; by L. A. Bauer -...-..._-..... 314 
XXXVI.—Studies in the Electro-magnetic Theory.—I. The ‘ 
law of electro-magnetic flux; by M. I.-Pupin___-____- 326 - 
SCIENTIFIC INTELLIGENCE. 
Chemistry and Physics—Conversion of the black to the red mercuric sulphide, 
W. SPRING, 342.—Color, density and surface tension of hydrogen peroxide, W. 
SPRING, 343.—Indirect Electrolysis of a liquid, E. ANDREOLI: Constituents of 
Cleveite gas, C. Runge and F. PascumEn, 344, 
Geology and Mineralogy—Glacial lakes in the Genesee vale H. L. FAIRCHILD, 
345.—Supplementary Notes on the Metamorphic Series of the Shasta Region © 
of California, J. P. SmirH: Ornithichnites and jaw bone from the Newark sand 
stone of New Jersey, A. M. EDwarps, 346.—Missouri Geological Survey— 
- Lead and Zinc Deposits, A. WinsLow: Geological Survey of Canada, 347.— 
Geological Society of America: La Géologie comparée, S. MEUNIER: Hruptiv 
gesteine des Kristianiagebietes: I Die Gesteine der Grorudit-Tinguait Serie, 
W. C. BroeGceEr, 348.—Directions for collecting rock specimens, 349.—Prelim- 
inary Report on the Marbles of Georgia, S. W. McCauiim: Some Swedish 
minerals, HJ. SJOGREN, 350. —Ueber gewundene Bergkrystalle, G. TSCHERMAK, 
351. 
Miscellaneous Scientific Intelligence—American Association for the Birk cos 
ment of Science, 352.—Iowa Academy of Sciences, 356. 
OpituaRy—Professor ©. V. RILEY, 356. 
