744 EEPOiiT— 1889. 



eeparate aud independent rails having slots seven-eighths of an inch in width het ween 

 them, through which the mechanical connections hetween the ' arrow ' and the 

 car hody pass. The tube is 8 inches in width, the bottom being 13 inches 

 below the surface of the road, this being an exceptionally small conduit as com- 

 pared with those in use for cable tramways, and, from its position under the side 

 rail, having the farther advantage of not needing the two centre rails. These rails 

 are supported by cast-iron yokes, to which they are securely bolted. The yokes 

 are placed at intervals of about 4 feet, excepting at the rail-joints, where they are 

 closer together. The sides and bottom of the tube are formed of Portland cement 

 concrete. At each rail-joint a special chamber is formed, having a convenient 

 removable lid, and in the.«e chambers are placed the * spring-jacks,' access being 

 obtained to them by lifting the lids of the chambers. 



The centre of the tube is placed somewhat inside the break in order that the 

 arrow ' shall not be directly underneath the slot, so as to avoid the danger of mud 

 and water from the road-surface falling directly on the ' arrow,' and also on the 

 ' spring-jack ' cheeks. The roof of the conduit is formed by a Z-shaped roof-plate. 

 The cable joining the ' spring-jacks' is laid in an independent 3-inch earthenware 

 pipe running from chamber to chamber, and in this pipe also is laid the unbroken 

 return-cable. 



The points and crossings are specially constructed to enable them to withstand 

 the weight of the ordinary traffic, a special device supporting the long unsupported 

 projection of the tongue over the conduit, at the same time allowing the mechanical 

 connections between the ' arrow ' and the car to pass. The narrowness of a 

 portion of the road required the construction of a length of double-single line — that 

 is to say, with three rails, so that, while keeping the tramcars on the proper side of 

 the road in the direction they are travelling, it makes it impossible for two tramcars 

 to pass each other in this narrow path. 



Two of the three rails are laid with conduits, the third being an ordinary 

 tramway rail. The mechanical connections between the ' arrow' and car body 

 consist of five shanks, these shanks being attached to cast-iron shoes or skates 

 which travel on the rail. The skates are connected together by light tie-bars 

 above the rail level, and the whole of the gear is drawn by means of chains 

 attached to the car bodj'. 



In series-running, by the employment of a current of constant value it is im- 

 possible for the most inexperienced car-driver to damage his motor by either too 

 rapid starting or by reversing whilst running. Indeed, it is a positive advantage in 

 descending a hill to check the speed of the car by altering the field connections so 

 that the armature tends to revolve in the opposite direction to that in which the 

 car is travelling, as the power that would otherwise be lost in braking the car is 

 actually added to that produced by the generator. 



This, in large systems with many cars and varying gradients, would appreciably 

 reduce the total power required to be generated, and the consequent consumption 

 of co.al. These advantages, combined with the efficiency of distribution as regards 

 the percentage of power lost in the conductors, with, at the same time, a low dif- 

 ference of potential at the terminals of each individual motor, may be regarded as 

 the main advantages of series-running. 



6. Teleplionic Gommunication hehueen London and Paris. 

 By W. H. Preece, F.E.S. 



The practicability of speaking by telephone between London and Paris has 

 recently been carefully examined both by the French and the English electricians. 

 The distance between the two places is i^75 miles, viz., 74 miles between London 

 and Dover, 21 miles from Dover to Calais, and 180 miles from Calais to Paris. It 

 is very easy to speak over such a distance if the wires be aerial and of thick copper, 

 but the insertion of underground A\are3 at each end and of a cable in the middle 

 places difficulties in the way that have to be surmounted. It is not a question of 

 apparatus, it is eolely the distribution of the electrical resistance and capacity 



