SCIENTIFIC NEAA^S. 



[Feb. 3, 1 888. 



to burst the pipe. According to Mr. Thomson's experi- 

 ments for a pipe | inch diameter it would require a length 

 of about seven inches to produce the burst by the expan- 

 sion of the water in the act of freezing. This would only 

 be sufficient to burst the pipe, but would not force it 

 open to the extent generally found after a thaw. The 

 surplus water freezing at the instant of release, and being 

 forced out in the expansion, would form a solid lump of 

 ice on the outside of the pipe, not a drop of water being 

 lost in the process of changing form. This must have 

 been frequently noticed. When a pipe, cyhnder, or 

 other vessel has been burst by the frost, the ice has been 

 seen projecting out several inches from the surface. This 

 is another instance of the flow of solid bodies, and is to 

 be seen in perfection among the Alpine glaciers, when 

 the molecules give way and accommodate themselves to 

 the ground over which they pass. 



— ■>-^«^'^*tf-» — 



THE LINEFF ELECTRICAL TRAMWAY 



THE various systems of electrical traction that have 

 been proposed up to the present may be divided 

 into conductor and battery systems. Secondary batteries 

 or accumulators are being gradually improved, and 

 though still made principally of lead, they will probably 

 be used for propelling carriages on long lines. The con- 

 ductor systems, however, present several important 

 advantages, especially for lines a few miles long, and any 

 difficulties that are likely to occur will be mechanical, 

 and can to a considerable extent be provided for by 

 careful design. 



Three systems of conductors have been proposed, one 

 being the overhead, which was used at the Paris Electric 

 Exhibition of 1881, where bare wires were hung on 

 poles by the side of the line, and a running collector 

 attached to the car by an insulated cable, travelled along 

 them. It appeared at first that no modification of such a 

 system would enable the branching of a line to be 

 provided for, but in the recent paper by Dr. E. Hopkin- 

 son, read at the Institution of Civil Engineers, it was 

 suggested that the wires might hang directly over the 

 car, and being left rather slack, they would make con- 

 tact with a bar on the top of the car. This useful paper 

 forms a landmark in the literature of the subject, although 

 it deals with a railway rather than a tramway. The 

 method there referred to has been adopted with marked 

 success at the points where the Bessbrook electric railway 

 crosses the public roads. A continuous contact is 

 provided by arranging a contact bar at each end of the 

 car, so that one span of wire touches the foremost bar, 

 before the connection has been broken at the rear. Such 

 a system is not admissible in a town which has any 

 regard for appearances, but seems well adapted to 

 suburban traffic. 



The Bessbrook line has a surface conductor, which 

 consists of an inverted channel of rolled steel, mounted 

 on prepared wooden supports, the return current flowing 

 through the rails. The highly successlul electric railway 

 at Brighton is not provided with a separate conductor, 

 the current merely passing from one rail to the other, 

 and the wheels being insulated from each other. Such 

 a method will only suffice for very short distances. The 

 method which has recommended itself to many engi- 

 neers as the most mechanical and trustworthy for 

 use in townis the channel system, in which the con- 

 ductor is carried out of sight, and if possible out of reach, 



in a channel or slit tube beneath the level of the road. 

 An electrical tramway has been at work at Blackpool 

 for some time, in which the channel system is employed. 

 It cannot, however, be said to be an entire success, 

 although the length is only a few miles, and the gradients 

 are imperceptible. The chief causes of difficulties have ' 

 been in insulating the conductor from the earth. On 

 short lines of a mile or so the insulation presents little 

 difficulty, for a fairly large current can be used at low 

 pressure. But when the line is several miles in length 

 there would be a serious loss if the electricity were not 

 supplied in a small current at a high pressure. For high 

 pressure, high insulation is necessary. Several highly 

 ingenious methods have been proposed for working a 

 number of cars in series — that is, the same current is 

 made to flow through each in succession ; but the details 

 are too complicated to be discussed here. There is a great 

 field tor comparatively short lines, and the latest system, 

 if not presenting any remarkably new departure, presents 

 several well-designed features. We refer to the Lineff 

 Electrical Tramway, of which a public trial was made a 

 few days ago at the depot of the West Metropolitan Tram- 

 way Company. About 80 yards of line have been, laid 

 down, and an extension, including a passing place with 

 points, was in process of construction. There is a con- 

 duit or channel between the rails, having an opening of 

 three-quarters of an inch on a level with the ground. 

 The channel is of concrete, about 6 inches thick, rendered 

 with cement, and a cast-iron chair at every two or three 

 feet presents a flush surface to the inside of the conduit. 

 The conductor is a bare copper wire in a gas pipe, which 

 acts as a conductor also, the wire serving to increase the 

 conductivity, and to ensure continuity. At intervals of 

 three feet six inches, iron crutches presenting a side view 

 similar to the rowlock of a boat, are screwed into the iron 

 pipe. These are the contact pieces, and are placed 

 on one side of the centre of the channel, so that they 

 are not visible from outside and are not within direct 

 reach of rain and dirt, though they might be got at by a 

 boy of an inquisitive turn of mind, by means of an iron 

 hoop. The collector on the car is a wire rope running 

 nearly its whole length, and with sufficient slack to 

 allow it to touch at least two of the contact pieces at the 

 time. The rope is covered with short lengths of brass 

 tube, with the view, we presume, of providing for wear. 

 This method of collecting offers great facilities for taking 

 the points when the line branches. The attachments ot 

 the collecting rope to the car, are strong, flat bars, which 

 are arranged to wedge up any stones that may be 

 jammed in the groove. The car was driven by an 

 Immisch motor series-wound, running at 1,000 revolu- 

 tions when the car travels at eight miles an hour. 



A rather rough regulator was arranged to control the 

 circuit when the current was switched on and oiT. 

 The car took about 10 amperes of current at a pressure 

 of 230 volts to run it at six to eight miles per hour. 

 This is equivalent to 45 horse-power, which is more 

 than we expected, considering the motor and the chain- 

 gearing used. The car is provided with a hinged board 

 at either end, which, on meeting with an obstacle, makes 

 a contact which puts on an electric break, and at the 

 same time reverses the motor. In an experiment to 

 test this, the car, running at about six miles an hour, 

 with half a dozen passengers, was stopped by a box 

 filled with sand, in about 2 ft., the box being pushed 

 that distance, and the car retiring from it at about three 

 miles an hour after the reversal. 



