SCIENCE. 



[Vol. XIII. No. 313 



and the knobs at M drawn so far apart that the sparks only passed 

 singly, then if a similar conductor, C, be brought up to k, a stream 

 of sparks was immediately observed. This action of C could only 

 be explained by supposing the current m gk was oscillatory. 



The reason that a powerful induction-coil gives rise to oscillatory 

 motion is, that, first, it charges the terminals C and C to a high 

 potential; second, it produces a spark in the intervening circuit; 

 and, third, as soon as the discharge begins, the resistance of the 

 air-space is so much reduced as to allow of oscillatory motion being 

 set up. If the terminal conductors are of very large capacity (for 

 example, if the terminals are in connection with a battery), the cur- 

 rent of discharge may indefinitely reduce the resistance of the air- 

 space : but, when the terminal conductors are of small capacity, 

 this must be done by a separate discharge, and therefore, under the 

 conditions of Hertz's experiments, an induction-coil was absolutely 

 essential for the production of oscillations. 



Hertz slightly modified the form of apparatus used to that shown 

 in Fig. 4, where the conductors C and C were in the same straight 

 line, three metres apart, with the discharger B at the centre. With 

 this arrangement, sparks were obtained in the micrometer circuit 

 when its distance from CBC was one and a half metres. Hertz 

 replaced the micrometer circuit shown in Fig. 4 by another, which 



^ 



^ c- y o ^<^ o (^ c- -y s> 



Fig. 4. 



consisted of two wires parallel with CBC, with knobs at their 

 ends, there being a micrometer, M, at the middle. Sparks were 

 obtained at the micrometer, as with the other form of circuit. 

 When the knobs at B were drawn so far apart that there was no 

 spark between them, there was still a spark at J/ due to the elec- 

 trostatic effect of charging C and C. By bridging across M with 

 a damp thread, this effect was got nd of ; but, when there were 

 sparks at B, there were sparks at /I/, even with the thread. So the 

 thread was sufficient to afford a passage to the comparatively slow 

 alternations of the coil-discharge, but was not sufficient to provide 

 a passage for the immeasurably more rapid alternations of the os- 

 cillatory current. 



If there really are oscillations of the nature of a regular vibration, 

 then an oscillatory current of a definite period would exert a much 

 greater inductive effect upon one of equal period than upon one 

 differing from it ; that is, we ought to get resonance phenomena 

 from currents, as from sound-vibrations. If two circuits are taken 

 having as nearly as possible equal periods of vibration, the effect 

 of one on the other will be diminished by altering either the 

 capacity or coefficient of self-induction of one of them, as a change 

 in either of these would alter the period of vibration of the circuit. 



(To he continued.^ 



Another Electric Road at Atlantic City, N.J. — We 

 take great pleasure in announcing in this issue of our paper a most 

 important indorsement of the electric system of street-railway pro- 

 pulsion. This indorsement comes from the Pennsylvania Railway 

 Company, who have during this last week, through the general 

 managers of that company, closed a most important contract with 

 the Sprague Electric Railway and Motor Company for the complete 

 equipment of their system of electric street-railways at Atlantic 



City, N.J. Before awarding this contract for the equipment of this 

 road, the Pennsylvania Railroad appointed a committee who should 

 have charge of making a most minute and careful investigation of 

 the merits of all the different systems of street-railway propulsion, 

 both electric and cable, now in use. The committee in charge of 

 the investigation were composed of mechanical and electrical ex- 

 perts of the highest class, and of wide reputation. The period of 

 investigation extended over five months, and during this time the 

 committee visited all the principal electric railways and cable roads 

 which are in operation in this country, and carefully examined the 

 operation of each. The Sprague Company are certainly to be con- 

 gratulated upon securing this contract. 



West End Electric Road at Boston. — The West End Elec- 

 tric Railway at Boston is running very successfully, and carrying a 

 large number of passengers each day between Park Square (one 

 terminus of the road) and Brighton (the other terminus of the road). 

 The cars run fast, and are under quick and perfect control. The 

 residents in Brookline who use the cars regularly in coming into 

 Boston and returning are enthusiastic over the time saved over the 

 ordinary horse-car. The change of the overhead to the under- 

 ground system is made very quickly, and without stop, so that no 

 delay is experienced at this point. The car-drivers, or " motorneers," 

 as some Bostonians persist in calling them, are not expert electri- 

 cians, but simply street-car drivers, who have been detailed to oper- 

 ate the electric cars, and who have learned their necessary duties 

 very quickly. All of these old drivers are enthusiastic over the ease 

 with which an electric car can be driven, and are well pleased with 

 their new position. On the 20th of January a very heavy snow- 

 storm reached the city, and covered the tracks of the railway to the 

 depth of from two inches to a foot. The electric snow-ploughs, 

 which are being equipped by the Sprague Coinpany for use by the 

 West End Road, had not been finished, and the cars were obliged 

 to run without this aid for clearing the tracks. In spite of this, the 

 cars ran very successfully over the entire distance of the roads, clear- 

 ing their own way, and carrying large numbers of passengers. The 

 president of the road and the directors expressed themselves as well 

 pleased with the demonstrated efficiency and strength of the electric 

 road, as exhibited during the snow-storm, even without the aid of 

 the regular Sprague electric snow-ploughs. The Boston Herald, in an 

 editorial of Jan. 17, in commenting on the road, said, " Those who 

 have made the experiment of taking a ride on the new electric rail- 

 way on Beacon Street must have come to the conclusion that this 

 method of securing rapid transit in the suburban wards is one of 

 the most promising that has yet been brought forward in this city. 

 The speed attained, where the conditions are favorable, is quite 

 equal to that of the elevated railroads in New York City, while the 

 structures supporting the electric wires are by no means as much of 

 a disfigurement as it was at one time supposed that they might be." 

 So long as a mixed service is maintained, — that is, so long as some 

 of the cars are drawn by horses, — the full advantage of the elec- 

 tric system cannot be realized. The speed of the electric car has 

 to conform to the speed of the horse-car which may be in front of 

 it ; but, if the experiment proves as successful as there is now every 

 reason to think that it may, the West End Company will before 

 long feel compelled to substitute electric for animal power in the 

 service of all of its lines. When that change is brought about, the 

 speed that can be made, even in the centre of the city, will be very 

 much accelerated over the average speed of to-day. 



A Southern Electric Railway started. — During the 

 past week the Asheville Electric Street Railway, which has been 

 in course of construction for the last month under the Sprague Elec- 

 tric Railway and Motor Company of New York, was successfully 

 put in operation. The first trial trip of the motor-cars was made 

 on Jan. 21, in presence of the president, Mr. W. P. Penniman, jun. ; 

 superintendent, Mr. J. H. Barnard ; and a number of prominent citi- 

 zens, — Capt. T. W. Patton, Gen. Jonstone Jones, Dr. S. D. Pelham, 

 and about sixty others ; some being stockholders in the road, and 

 others interested, directly or indirectly, in the success of the enter- 

 prise. The test proved a great success. The run was made over 

 the entire distance of the line, about two miles, in less than eight 

 minutes, carrying a large number of passengers. The citizens of 

 Asheville are enthusiastic over the new electric line, and the direc- 



