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belonging to the early days of electrical invention in Holland, 

 apparatus belonging to Volta, an autograph of Galvani, Wheat- 

 stone's revolving mirror for measuring the velocity of electricity, 

 and Faraday's iron ring with two coils of wire wound on it, by 

 the aid of which he made his first observation of induced 

 currents. 



Outside the Exhibition there was the Electric Tramcar, con- 

 veying passengers over a tramway a quarter of a mile long, from 

 the Place de la Concorde to the Exhibition, and driven by an 

 invisible influence conducted to it by means of two travelling 

 wires, which had one end fastened to the car, while the other 

 end travelled along a light rail suspended on posts beside the 

 line. These two wires, it is to be remarked, did not drag the 

 car, but were visibly dragged by it, a circumstance which brought 

 home forcibly to one's mind the mysterious character of the 

 unseen propelling agent. The current conveyed by these wires 

 passed through an electromotor beneath the floor of the car, 

 causing its armature to rotate and drive the wheels. The 

 current itself was produced by a dynamo machine in the centre 

 of the exhibition building, and this machine was almost precisely 

 similar to the electromotor ; for it is a general property of a 

 large class of electro-magnetic machines that they can either be 

 used for furnishing a current, or can themselves be driven by a 

 current supplied to them from without. 



The Exhibition was open to the public from 10 a.m. to 6 

 p.m., and then after being closed for two hours was open again 

 from 8 to n. The evening was the time when it was most 

 crowded, and on three evenings in the week there was an extra 

 crowd in one of the galleries, where some hundreds of people 

 were standing in queues waiting their turn to be admitted to 

 one of four rooms which were inscribed with the words, " Tele- 

 phone de l'Opera." In each of these rooms there were twenty 

 pairs of telephones hung on panels round the walls and having 

 flexible wire cords attached to them, which were in communi- 

 cation with the Opera House, some two miles distant. On 

 putting one of these pairs of telephones to your ears you dis- 

 tinctly heard the music that was being performed at the Opera; 



