Page:Popular Science Monthly Volume 15.djvu/876

 exception of the Herschels, a few years ago nobody attempted to solve these questions. Melloni was among the first to give the subject serious attention. He used the thermopile and the galvanometer in his researches. Fraunhofer prepared the way for the spectroscope, and in 1860 the employment of that instrument by Kirchhoff opened the pathway of the modern science of solar physics. At first we knew little more than that the sun was a hot globe, with occasional spots on its surface; now the work has been divided into special fields of research. Professor Langley here recounted, in considerable detail, the labors of the great modern physical astronomers, but our space is too circumscribed even to give a synopsis of his remarks. In concluding, he pointed out the practical value of many of these researches. The direction in which to look for the resolving of elements into simpler forms may be indicated by solar analysis. The real nature of terrestrial elements may thus be ascertained. The problems of meteorology may find their ultimate solution in studies of the sun, and enable us to predict the years of dearth or plenty in our harvests. But as yet none of us are able to prophesy the weather for even the coming week from our knowledge of the sun. A more promising field of utility is opened in the construction of solar engines. These may be made at some future day to employ the sun's heat to better advantage than we now use steam, power. At present our science teaches us to look for a period, in the far-distant future, when our sun's fires shall become extinct, and earth a frozen orb. The glacial era tells us of a previous epoch, when life may have been equally restricted by cold, and we are thus taught that the human race is the creature of yesterday, and can not endure for ever.

The Coal of the Future.—In a paper on the anthracite coal-fields of Pennsylvania, Mr. P. W. Sheafer estimated the production of that kind of coal in 1820, when anthracite mining was begun, at 365 tons; it is now 20,000,000 tons per annum. According to Mr. Sheafer, only one third of the coal goes into market; the other two thirds is wasted, being lost in the mines and in preparation. The maximum product he estimated at about 50,000,000 tons per annum, and, at the present rate of increase, this limit will be reached in the year 1900. At that rate the anthracite coal-fields would be exhausted in 186 years, say in the year 2065. Then we must have recourse to our bituminous coal-fields, whose area reaches the enormous extent of 200,000 square miles, or four hundred times the area of the anthracite. The competition between the several anthracite coal companies, and between them and the producers of bituminous coal, will always keep the price moderate. Mr. Sheafer doubted if Great Britain could much increase its present enormous product of 136,000,000 tons, but at her present rate of increase she will have exhausted her coal at about the time when our anthracite resources are at an end.

Origin of Certain Mound-Formations in California.—A correspondent of the "Monthly" in the number for December, 1878, described the curious hummocky appearance of the surface of the ground in the Yosemite Valley, and expressed a wish to have the phenomenon explained. It appears that a similar surface-conformation is to be seen in many other parts of California, and Dr. G. W. Barnes offers an explanation of its origin in a paper in the "American Naturalist," on "The Hillocks or Mound-Formations of San Diego." According to Dr. Barnes, these mounds, in their most common type, may be described as rounded eminences or knolls, rising from one to four feet above the surrounding surface or the depressions between them, and ranging from ten to fifty feet in diameter. Each mound, he says, marks a spot where formerly grew a shrub, or cluster of shrubbery, which served to fix its location, and which exercised an important influence in the successive stages of its development. Dust set in motion and borne along by the winds is arrested by the shrub, and together with its fallen leaves accumulates within and around it, often nearly enveloping the whole plant, The gopher, subsisting upon roots and preferring for its operations the loose soil about them, is, in exceptional cases, an adjunct of the wind in heaping up material about the plant. While the loose earth of which the deposit is composed is