2o6 THE POPULAR SCIENCE MONTHLY. 



plicity. In this connection the names of Reiss, Graham Bell, Edison, 

 and Hughes, are those chiefly deserving to be recorded. 



"While electricity has thus furnished us with the means of flashing 

 our thoughts by record or by voice from place to place, its use is now 

 gradually extending for the achievement of such quantitative effects 

 as the production of light, the transmission of mechanical power, and 

 the precipitation of metals. The principle involved in the magneto- 

 electric and dynamo-electric machines, by which these effects are ac- 

 complished, may be traced to Faraday's discovery in 1831 of the in- 

 duced current, but their realization to the labors of Holmes, Siemens, 

 Pacinotti, Gramme, and others. In the electric light, gas-lighting has 

 found a formidable competitor, which appears destined to take its 

 place in public illumination, and in lighting large halls, works, etc., 

 for which purposes it combines brilliancy and freedom from obnoxious 

 products of combustion, with comparative cheapness. The electric 

 light seems also to threaten, when subdivided in the manner recently 

 devised by Edison, Swan, and others, to make inroads into our dwell- 

 ing-houses. 



By the electric transmission of power we may hope some day to 

 utilize at a distance such natural sources of energy as the Falls of 

 Niagara, and to work our cranes, lifts, and machinery of eveiy descrip- 

 tion by means of sources of power arranged at convenient centers. To 

 these applications the brothers Siemens have more recently added the 

 propulsion of trains by currents passing through the rails, the fusion 

 in considerable quantities of highly refractory substances, and the use 

 of electric centers of light in horticulture as proposed by Werner 

 and William Siemens. By an essential improvement by Faure of 

 the Plante secondary battery, the problem of storing electrical energy 

 appears to have received a practical solution, the real importance of 

 which is clearly proved by Sir W. Thomson's recent investigation of 

 the subject. It would be difficult to assign the limits to which this 

 development of electrical energy may not be rendered serviceable for 

 the purposes of man. 



As regards mathematics, I have felt that it would be impossible for 

 me, even with the kindest help, to write anything myself. Mr. Spot- 

 tiswoode, however, has been so good as to supply me with the follow- 

 ing memorandum : 



In a complete survey of the progress of science during the half-cen- 

 tury which has intervened between our first and our present meeting, 

 the part played by mathematics would form no insignificant feature. 

 To those, indeed, who are outside its enchanted circle it is difficult to 

 realize the intense intellectual energy which actuates its devotees, or 

 the wide expanse over which that energy ranges. Some measure, 

 .however, of its progress may perhaps be formed by considering, in 

 one or two cases, from what simple principles some of the great recent 

 developments have taken their origin. 



