THE ELECTRIC RAILWAY. 



749 



Fig. 3. 



tacks the lead plate to which it goes, thus forming peroxide of lead, 

 and the hydrogen reduces any oxide that may be on the other lead 

 plate, thus producing pure lead, some of the surplus 

 hydrogen forming as a film upon the surface. The 

 charging current is then reversed, so that the latter 

 plate is now attacked, and is then reversed again ; 

 the effect of these operations being to render the 

 surfaces of both lead plates porous so that they pre- 

 sent a large surface, and can therefore hold a great 

 deal of peroxide of lead. When the charging cur- 

 rent is broken, the oxygen, which has been forcibly 

 separated from the liquid, seeks to recombine in the 

 same way that a stone which has been forcibly sep- 

 arated from the earth seeks the earth when liberated. 

 If now the two lead plates be joined with a wire, the 

 effect of the oxygen in the peroxide of lead trying 

 to recombine is to generate an electrical current in 

 the opposite direction to the original one ; and this 

 is the current which is utilized. The value of accu- 

 mulators would be much increased if this return cur- 

 rent could be made greater, and if the weight and 

 cost of the accumulators themselves could be made less. At pres- 

 ent, however, their use is restricted by reason of their great cost and 

 weight, and by the small ratio (about fifty per cent in practice) of the 

 electrical energy returned to that expended in charging them. Never- 

 theless, the fact that the accumulator system of electric railroading 

 obviates the necessity for any conductors, which sometimes are incon- 

 venient and expensive, and which themselves occasion great loss of 

 electrical energy, leads many to believe that for short routes, as upon 

 street-car lines of cities, accumulators will be very efficient. 



At the Chicago Exposition of Railway Appliances, which has just 

 closed, the system of Messrs. T. A. Edison and S. D. Field, of New 

 York, was tried, and with undeniable success. By this system a third 

 conductor is used ; but it is not placed upon poles, as in the Siemens 

 system (for this would not be practicable in the streets of a city), but 

 lies in a long sunken trough which runs between and parallel to the 

 rails. The trough is covered, and a long and very narrow slit runs the 

 whole length of the cover. Through this slit extends a strong metallic 

 rod which is connected mechanically with a contact-carriage lying 

 upon the conductor, and which is mechanically and electrically con- 

 nected with the car. 



It is claimed that by means of a scraper, carried by the contact- 

 carriage, there will be no trouble occasioned by any accumulation on 

 the conductor of ice, snow, or mud, but that the car can be satisfac- 

 torily run in all kinds of weather. 



Fig. 4 represents the generator and track as arranged at the Chi- 



