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POPULAR SCIENCE MONTHLY. 



ber of hearings on the subject, pub- 

 lished in a pamphlet of 240 pages, and 

 has drawn up a careful report. This 

 report covers familiar ground, but 

 in an unusually clear and straightfor- 

 ward manner. The attitude of Wash- 

 ington, Jefferson and Adams is referred 

 to, and the history of the metric sys- 

 tem of weights and measures is briefly 

 reviewed. It is pointed out that the 

 adoption of a decimal system of coin- 

 age in the United States was one of 

 the strongest influences leading to the 

 adoption of the metric system by 

 France, and that Great Britain and the 

 United States are practically the only 

 non-metric countries. The weights and 

 measures of Great Britain and the 

 United States are not identical as is 

 generally supposed, and there is no 

 chance whatever that either system 

 will become a universal system. The 

 metric system has become necessary 

 for scientific work; it would decrease 

 the cost and labor of education; it 

 would give unity to our manufactures, 

 and is almost necessary for the exten- 

 sion of our commerce. The admitted 

 expense and trouble involved in the 

 adoption of the system are less, as has 

 been shown in other countries, than is 

 feared, and in any case the longer the 

 adoption is delayed the greater will be 

 the difficulty. The scientific, manufac- 

 turing and commercial interests of the 

 country are under great obligations to 

 Mr. John F. Shafroth, who, as chair- 

 man of the house committee on coin- 

 age, weights and measures, has devoted 

 much careful attention to the subject. 



THE CAUSES OF VOLCANIC ERUP- 

 TIONS. 

 The recent volcanic outbreaks in the 

 Lesser Antilles have naturally aroused 

 much popular and scientific interest in 

 these geological phenomena and have 

 made a brief statement of current and 

 accepted explanations of them a matter 

 of interest. All these manifestations 

 of heat are derived from the great 

 stores which exist in the interior of the 

 earth. The consideration of them and 



of the known increase of temperature 

 with depth led earlier geologists to be- 

 lieve that the earth possessed a heated 

 molten core and a cold and relatively 

 thin exterior shell. But as further in- 

 vestigation developed correct concep- 

 tions of the rigidity of the globe in 

 resisting strains produced by its rota- 

 tion and the attraction of other 

 heavenly bodies for its mass; and as 

 the elevating effect upon the fusing 

 points of rocks of an increase of 

 pressure was realized, it was seen 

 that the earth is practically solid clear 

 through and that local reservoirs of 

 molten rock beneath volcanic districts 

 are alone admissible. That local reser- 

 voirs exist seems quite well established, 

 and that the rock is sufficiently fluid 

 to enable complex parent magmas to 

 break up into various differential prod- 

 ucts is the latest result of the investi- 

 gation of eruptive areas. Volcanoes 

 are moreover arranged along great 

 lines of geological disturbance and 

 fracture as shown in the accompanying 

 illustration. The fractures are natur- 

 ally the conduits through which the 

 great tension of the internal molten 

 masses is eased by eruptions. The im- 

 mediate propulsive force which drives 

 the lava to the surface is the next topic 

 of importance which challenges atten- 

 tion. Some geologists believe that the 

 contraction of the globe and the sink- 

 ing of one side of the great fractures 

 above referred to force out the lava as 

 juice might be squeezed through a rent 

 in an orange. Others, however, attrib- 

 ute the propulsion to the vapors which 

 are held dissolved or occluded in the 

 lava and which are so much in evidence 

 at times of eruption. The frightful ex- 

 plosions and the vast exhibitions of 

 power which they present give much 

 force to this conception. Imagine then 

 a rising tide of lava. As it forces its 

 way through the conduit it spreads 

 earthquake shocks abroad. Reaching 

 the surface its dissolved vapors explode 

 with greater and greater violence and 

 scatter tuffs and breccias over the 

 neighboring country. They may rend 



