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THE POPULAR SCIENCE MONTHLY. 



force, many workers and many tliinkers 

 have helped to build up the nineteenth-cen- 

 tury school of plenum one ether for light, 

 heat, electricity, magnetism ; and the German 

 and English volumes containing Hertz's elec- 

 trical papers, given to the world in the last 

 decade of the century, will be a splendid 

 monument of the consummation now real- 

 ized. The Eoyal Society's Transactions and 

 Proceedings of the last forty years contain, 

 in the communications of Gassiot, Andrews 

 and Tait, Cromwell, Yarley, De la Rue and Miil- 

 ler, Spottiswoode, Moulton, Pliicker, Crookes, 

 Grove, Robinson, Schuster, J. J. Thomson, 

 and Fleming, almost a complete history of 

 the new province of electrical science, which 

 has grown up largely in virtue of the great 

 modern improvements in practical methods 

 for exhausting air from glass vessels, by which 

 we now have " vacuum tubes " and bulbs 

 containing less than TyoVoTT of the air which 

 would be left in them by all that could be 

 done in the way of exhausting (supposed to 

 be down to one millimetre of mercury) by 

 the best air-pump of fifty years ago. A large 

 part of the fresh discoveries in this province 

 have been made by the authors of these 

 communications, and their references to the 

 discoveries of other workers very nearly 

 complete the history of all that has been 

 done in the way of investigating the trans- 

 mission of electricity through highly rarefied 

 air and gases since the time of Faraday. 



Paleontological Riches of Texas. In 



his report to the State Geological Survey on 

 the Invertebrate Paleontology of the Texas 

 Cretaceous, F. W. Cragin characterized the 

 State as a mine of paleontological research, 

 particularly with respect to the extensive 

 and as y(*t little known faunae of its Co- 

 manche series. The work of the recently 

 deceased Dr. Roemer, the little illustrated 

 but mainly accurate paleontological woi-k of 

 Dr. Shumard, the work of Conrad upon the 

 collections made by the Mexican Boundary 

 Survey, not to mention numerous lesser con- 

 tributions by Marcou, White, Hill, Giebel 

 Schlueter, and others, all taken together, 

 have only tapped this great mine of knowl- 

 edge. And this, as regards invertebrate 

 forms alone ; for the vertebrates of the Texas 

 Cretaceous, and particularly those vertebrate 

 faunas which are of the greatest importance 



as factors of the stratigraphic and taxonomic 

 problems of the lower rocks of the Comanche 

 series, are almost wholly unknown. Of the 

 remains of Cretaceous invertebrate organisms 

 a great wealth of material has been accumu- 

 lated by the survey, including types of many 

 new forms of exact biological and strati- 

 graphical significance. 



Manganese in Alabama. A report on the 

 geological structure of Murphree's Valley, 

 Alabama, made to the State Geologist by 

 Assistant A. M. Gibson, shows that besides 

 limestone and hematite and limonite iron 

 ores, the estimates of the value of which 

 have been confirmed in the working, it con- 

 tains manganese ores and beds of fine clays. 

 Half a dozen or more spots are described, all 

 in the same region, where deposits of man- 

 ganese ores, chiefly pyrolusite, of good qual- 

 ity, have been seen. The discoveries of these 

 deposits have been in the main accidental, 

 and they cover only a very small part of the 

 ground where ores are presumed to exist. It 

 is therefore probable that the larger propor- 

 tion of the beds still remain undiscovered. 

 The clays comprise brick clays and halloy- 

 site or porcelain clay a similar bed to which 

 has been worked with satisfactory results in 

 De Kalb County along with which are a 

 honestone grit, sandstones, and honestones 

 suitable for building, and a fireproof con- 

 glomerate. Besides two lines of exposure 

 of iron ores and one of carboniferous lime- 

 stone, this valley is favored with " ample coal 

 accessible on both sides at its very edge." 



Arago's Work. In his address at the 

 unveiling of a statue of Arago, in Paris, 

 June 11th, M. Tisserand said that "Arago 

 introduced physics into astronomy, and gave 

 it a permanent place. Before him, astrono- 

 mers concerned themselves chiefly with the 

 movements of the stars and the members of 

 our planetary system, seeking to explain 

 them in their minutest details by the law of 

 gravitation. Arago studied the nature of 

 the heavenly bodies, and the character of 

 the phenomena continually exhibited by 

 them. The polariscope showed him that 

 the glaring surface of the sun is gaseous, 

 and gave him important information as to 

 the light of comets. Another application of 

 physical methods furnished him with a pre- 



