vi CONTENTS. 
Number 298. 
Page 
Art, XXIX.—Recent Progress in Optics; by W. LeContsE 
DERVENS) Song ii./ul 2) ..056 Se ee e277 
XXX.—Quantitative Deterraination of Perchlorates; by D. 
Ad KICREIDER .'s2..¢ _.'.. 4. 2: eee 287 
XX XI.—Occurrence of Copper in Western Idaho; by R. L. 
PACKARD 2.22 2.2. . 22 ose eee 298 
XX XII.—Demonstration of Caustics; by R. W. Woop -.-. 301 
XXXIU.—Spectrum of Helium; by W. Crooxss.--.----- 302 
XXXIV.—Igneous Rocks of the Sweet Grass Hills, Mon- 
tana; by W. H. Wzep and L. V. Pirsson._..-..-. 309 
XXXV.—Distribution and Secular Variation of Terrestrial 
Magnetism, No. Ill; by L. A, BauER 2__. 2.22 22ers 
XXXVI.—Studies in the Electro-magnetic Theory.—I. The 
law of electro-magnetic flux; by M. 1. 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. PascHEN, 344. 
Geology and Mineralogy—Glacial lakes in the Genesee valley, H. L. FAIRCHILD, 
345.—Supplementary Notes on the Metamorphic Series of the Shasta Region 
of California, J. P. Smita: Ornithichnites and jaw bone from the Newark sand 
stone of New Jersey, A. M. Epwarps, 346.—Missouri Geological Survey— 
Lead and Zinc Deposits, A. WinsLow: Geological Survey of Canada, 347.— 
Geological Society of America: La Géologie comparée, 8S. MEUNIER: EHruptiv- 
gesteine des Kristianiagebietes: I Die Gesteine der Grorudit-Tinguait Serie, 
W. C. BroaeeEr, 348.—Directions for collecting rock specimens, 349,—Prelim- 
inary Report on the Marbles of Georgia, S. W. McCautiz: Some Swedish 
minerals, HJ. SJ6GREN, 350.—Ueber gewundene Bergkrystalle, G. TSCHERMAK, 
35]. 
Miscellaneous Scientific Intelligence —American Association for the Advance- 
ment of Science, 352.—Iowa Academy of Sciences, 356. 
OBITUARY —Professor C. V. Riuey, 356. 
