8;6 



THE POPULAR SCIENCE MONTHLY. 



exception of the Herschels, a few years ago 

 nobody attempted to solve these questions. 

 Melloni was among the first to give the sub- 

 ject serious attention. He used the ther- 

 mopile and the galvanometer in his research- 

 es. 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 occasion- 

 al spots on its surface ; now the work has 

 been divided into special fields of research. 

 Professor Langley here recounted, in consid- 

 erable 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 re- 

 solving 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 promis- 

 ing field of utility is opened in the construc- 

 tion 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 Fntnre. 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 anthra- 

 cite mining was begun, at 365 tons ; it is 

 now 20,000,000 tons per annum. Accord- 

 ing 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 an- 

 num, 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 an- 

 thracite. The competition between the sev- 

 eral 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 Monad-Formations in 

 California. A correspondent of the " Month- 

 ly" in the number for December, 18*78, de- 

 scribed 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 Natu- 

 ralist," on " The Hillocks or Mound-Forma- 

 tions of San Diego." According to Dr. 

 Barnes, these mounds, in their most com- 

 mon 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 for- 

 merly grew a shrub, or cluster of shrub- 

 bery, which served to fix its location, and 

 which exercised an important influence in 

 tire successive stages of its development. 

 Dust set in motion and borne along by the 

 winds is arrested by the shrub, and togeth- 

 er 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 



