138 



THE POPULAR SCIENCE MONTHLY. 



principles of .stoichiometry, and work, as far 

 as possible, quantitatively. 



Physics at the American Association. — 



In the Section of Physics, Professor S. P. 

 Langley read a paper on the sources of in- 

 visible radiations and on the recognition of 

 hitherto unmeasured wave - lengths. The 

 object of the researches he described was 

 to ascertain whether there are other wave- 

 lengths than those found in the sun's heat, 

 so that we may perhaps explain how it is 

 that the surface heat of our planet is main- 

 tained in spite of the ready radiation of ex- 

 treme solar heat through the atmosphere. 

 We have in the infra-red portion of the so- 

 lar spectrum the greater part of the heat 

 which sustains organic life on this planet, 

 and the questions arise, Docs the planet ra- 

 diate heat of the wave-lengths that it re- 

 ceives from the sun ? and how is its tem- 

 perature maintained, probably several hun- 

 dred degrees above the temperature of space, 

 when our observations show that the direct 

 radiations of heat from the sun can only 

 raise it about fifty degrees above the sur- 

 rounding temperature ? Experiments at Al- 

 legheny show that the dark solar heat is 

 transmitted by our atmosphere with less 

 difficulty than the light ; and, if the radia- 

 tions of the soil are of this wave-length, our 

 planet should actually be cooler on account 

 of its atmosphere than if it had none. Pro- 

 fessor Langley has for two years past made 

 measurements of the radiations from bodies 

 of the temperature of the earth, using for 

 his experiments prisms and lenses of rock- 

 salt. From the results of these researches, 

 he says that we have every reason to believe 

 that heat radiated by the soil lias a wave- 

 length twenty times that of the lowest visi- 

 ble line of the solar spectrum. His experi- 

 ments thus tend to show that this heat is of 

 a totally different quality from that received 

 from the sun. Among the other papers read 

 in this section were those of Professor II. 

 S. Carhart on surface transmission of elec- 

 trical discharges, in revision of work by Pro- 

 fessor Henry ; of Professor E. L. Nichols, 

 on the chen^ical behavior of magnetic iron ; 

 of Major 11. E. Alvord, on the results of tele- 

 metric observation at Houghton Farm ; and 

 of Commander Theodore F. Jewell, on the 

 apparent resistance of a body of air to a 



change of shape. In the experiments on 

 this subject, a disk of gun-cotton was ex- 

 ploded on a metal plate. Each of the disks 

 had the letters " U. S. N " and the year of 

 manufacture stamped upon it. After ex- 

 plosion upon the iron, similar indentations 

 were found upon the plate, as if the air in 

 the indented letters had been driven into it. 

 Professor E. L. Nichols stated that from 

 comparisons he had made of the spectrum 

 of the unclouded sky with that of the sun- 

 light reflected by magnesium carbonate, he 

 had deduced the conclusion that the spec- 

 trum of the sky is of the same character as 

 that of white light. The blue color of the 

 sky and of other opalescent media is, ac- 

 cording to these and other correlative ex- 

 periments, not due to an excess of the more 

 refrangible rays in the light reflected by them, 

 but is of a subjective character. These re- 

 sults disagree with those obtained by Pro- 

 fessor Langley in his experiments. Mr. II, 

 Helm Clayton, of Ann Arbor, presented evi- 

 dence favoring the supposition that there 

 are at times slow progressive movements of 

 barometric change, and of temperature from 

 west to east, and attempted to show that 

 the weather of the United States during the 

 last year had been marked by certain peri- 

 odicity of character. 



Plants growing at Strange Heights. — 



Many anomalies have been observed in the 

 distribution of plants by altitude, which M. 

 F. Krasan has endeavored to account for, in 

 Engler's " Annuaire botanique," by suppos- 

 ing changes to have taken place during the 

 recent period in the height of the mount- 

 ains on which the vegetation is found. 

 Thus, in several valleys of the Alps, oaks 

 are growing at unusual altitudes, and live 

 under climatic conditions that seem to ex- 

 clude them elsewhere. They do not, how- 

 ever, appear to be reproducing themselves, 

 and are probably destined to be crowded 

 out by the beeches. On the Humberg, in 

 Southern Styria, at a height of between 750 

 and 1,360 feet, are found growing in the 

 midst of vines and associated with south- 

 ern plants masses of purely Alpestrine spe- 

 cies ; and in the mountain-region north of 

 Cilli, the highest altitude of which is less 

 than 3,000 feet, are not less than fift)'-one 

 species that occur normally in the region of 



