principles of stoichometry, 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 invisible radiations and on the recognition of hitherto unmeasured wave-lengths. The object of the researches he described was to ascertain whether there arc other wavelengths than those found in the sun's heat, 60 that we may perhaps explain how it is that the surface heat of our planet is maintained in spite of the ready radiation of extreme solar heat through the atmosphere. We have in the infra-red portion of the solar spectrum the greater part of the heat which sustains organic life on this planet, and the questions arise. Does the planet radiate heat of the wave-lengths that it receives from the sun? and how is its temperature maintained, probably several hundred 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 surrounding temperature? Experiments at Allegheny show that the dark solar heat is transmitted by our atmosphere with less difficulty than the light; and, if the radiations of the soil are of this wave-length, our planet should actually be cooler on account of its atmosphere than if it had none. Professor 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 has a wavelength twenty times that of the lowest visible line of the solar spectrum. His experiments 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 H. S. Carhart on surface transmission of electrical discharges, in revision of work by Professor Henry; of Professor E. L. Nichols, on the chemical behavior of magnetic iron; of Major H. E. Alvord, on the results of telemetric 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 exploded on a metal plate. Each of the disks had the letters "U. S. N" and the year of manufacture stamped upon it. After explosion 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 sunlight reflected by magnesium carbonate, he had deduced the conclusion that the spectrum 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, according to these and other correlative experiments, not due to an excess of the more refrangible rays in the light reflected by them, but is of a subjective character. These results disagree with those obtained by Professor Langley in his experiments. Mr. H. Helm Clayton, of Ann Arbor, presented evidence favoring the supposition that there arc 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 periodicity 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 supposing changes to have taken place during the recent period in the height of the mountains 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 exclude them elsewhere. They do not, however, 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 southern plants masses of purely Alpestrine species; and in the mountain-region north of Cilli, the highest altitude of which is less than 3,000 feet, are not less than fifty-one species that occur normally in the region of
