VIBRATION OF ROCKS IX PATAPSCO VALLEY. 541 



But we have not yet reached the end of our excursion ; indeed, we have 

 only entered the threshold of the scientist's sanctum, and the wonders 

 of the arcanum eclipse those of the portico. That mysterious agency 

 or force called electricity has been utilized, not merely for the benefit 

 of bulls and bears, or for hundreds of utilitarian purposes with which 

 we are familiarized every day, but it has been used as a fairy-finger 

 to probe Nature's hidden structure, and, as it were, enable us to feel 

 what the spectroscope has revealed to sight. 



Then, again, appliances for obtaining little samples of "stellar 

 space " in the interior of glass bulbs bottled vacuity which we may 

 examine at our pleasure, are in themselves curious. Think of a bulb 

 about the size of a cricket-ball containing only one ten-millionth part 

 of one atmosphere, and that part being subdivided into millions and 

 millions and millions of individual portions, and these particles being 

 captured and made to do visible, tangible work ; think of a miniature 

 engine with a propeller-wheel being made to revolve and a little rail- 

 way run by projecting these minute particles against the driving-wheel ; 

 think of a piece of refractory metal like platinum being so terribly 

 battered by hitting it in rapid succession with a charge of these little 

 molecules that it is made to cry out in fervent heat, to glow with a 

 bright light, and, if this molecular bombardment is continued, even to 

 melt before it like wax ; think of the commonest and most uninter- 

 esting materials, like burned oyster-shells, being made to shine with a 

 luminosity rivaling the " great carbuncle," or the famous " Kohinoor " ; 

 of little pieces of glass outvying the finest emeralds, rubies, and sap- 

 phires, when under this marvelous influence then, we will be ready 

 to admit that, while we work-a-day, matter-of-fact people may not 

 understand the motive that induces the original investigator to plod 

 on in his narrow path, continually prying into some seemingly trivial 

 corner of Nature's vast store-house of knowledge, we can nevertheless 

 appreciate and enjoy the beautiful results which modern Science has 

 to offer as rewards to her votaries, and we can not too greatly venerate 

 the genius of those who could conceive the possibility of such results, 

 and possess the ability to produce them. 



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YIBEATION OF BOCKS IN PATAPSCO VALLEY, 



MARYLAND. 



By FKEDEEIC GAEEETSON, M. D. 



THE valley of the Patapsco River, through which the Baltimore 

 and Ohio Railroad passes, presents many interesting subjects to 

 the student of physics and of geology. After passing the junction 

 of the Washington branch at the Relay House, eight miles west of 



