28 JOHN J. STEVENSON 



mental discoveries, and since that time everything has been 

 elaboration. 



Oersted's discovery respecting the influence of an electric 

 current; closely followed by that of Arago in the same direc- 

 tion, opened the way for Faraday's complete discovery of 

 induction, which underlies the construction of the dynamo. 

 This ascertained, the province of the inventor was well defined 

 — to conjure some mechanical appliance whereby the principle 

 might be utilized. But here as elsewhere the work of dis- 

 covery and that of invention went on almost pari passu; the 

 results of each increased those of the other. The distance 

 from the Clark and Page machines of the middle thirties, with 

 their cumbrous horseshoe magnets and disproportionate ex- 

 penditure of power, to the Siemens machine of the fifties was 

 long, but it was no leap. In like manner slow steps marked 

 progress thence to the Gramme machine, in which one finds 

 the outgrowth of many years of labor by many men, both 

 investigators and inventors. In 1870, forty years after Fara- 

 day's announcement of the basal principle, the stage was 

 reached whence progress could be rapid. Since that time 

 the dynamo has been brought into such stage of efficiency 

 that the electromotor seems likely to displace not merely the 

 steam engine, but also other agencies in direct application of 

 force. The horse is passing away and the trolley road runs 

 along the country highway; the longer railways are consider- 

 ing the wisdom of changing their power; cities are lighted 

 brilliantly where formerly the gloom invited highwaymen to 

 ply their trade, and even the kitchen is invaded by new meth- 

 ods of heating. 



Long ago it was known that if the refining of pig iron be 

 stopped just before the tendency to solidify became pro- 

 nounced the wrought iron is more durable than that obtained 

 in the completed process. Thus, imperfectly refined metal 

 was made frequently, though unintentionally and ignorantly. 

 A short railroad in southwestern Pennsylvania was laid in 

 the middle sixties with iron rails of light weight. A rail's life 

 in those days rarely exceeded five years, yet some of those 

 light rails were in excellent condition almost fifteen years after- 

 wards, though they had carried a heavy coke traffic for sev- 



