tions made therefrom), and the C. and P. D. at the terminals measured, the energy developed being absorbed by any form of R convenient. A curve showing the C. and generator P. D. at various loads is constructed from data so obtained. If desirable curves are made showing the output at various speeds. These curves are called "characteristics," and bear much the same relation to a dynamo that an indicator diagram does to a steam engine.

In some cases it is well to prove the dynamo by "shortcircuiting" it, and sometimes by suddenly "open-circuiting" it. Also to test the effect of slight variations in the position of the brushes.

From a financial standpoint the output per pound expended is evidently of importance, and under the same head can generally be placed, though to a lesser degree, the output per square foot of floor space occupied; and, where height must be considered, the output per cubic foot of space, and sometimes also per pound of weight. In most station work, however, the weight and height need not be considered as between dynamos of the same output. A large dynamo is cheaper and occupies less floor space per watt developed than its equivalent in smaller ones.

The allowance for repairs is generally figured as a certain percentage of the first cost, and is determined by experience. This is a very uncertain quantity, but where great care is taken to properly clean the dynamo, and keep the same in good condition (such as shellacing impaired insulation, etc.), and where open and short circuits do not occur on the line when operating, and the lightning arresters act properly, the repairs upon dynamos are usually very small, possibly not 2 per cent. per annum of the cost. In other cases it may reach any imaginable figure.

The output per pound of attendance to clean is, more or less, the reciprocal of the above. The more cleaning, the less repairs. Some dynamos, however, take much longer to clean than others, and some can never be thoroughly cleaned. The cleaning of dynamos is quite an expense in a large station, and an even larger percentage of cost in a small one, as a comparatively expensive man may have to do it at times when otherwise he might be more productively engaged.

The output per pound of attendance while running varies greatly. With some dynamos and their auxiliary mechanisms so much attendance is necessary as to be a considerable item in a small station, taking all of one man's time in a medium-sized station, and the time of more than one man if a large number of dynamos are running. This emphasises the fact, which no one not an operating manager and superintendent of a station fully realises, that in choosing a system there are many points to be considered besides commercial efficiency, first cost and electrical output of the character desired and as indicated by the characteristic curve. The mechanical design should be such that the electrical functions of the different parts may not be destroyed by reason of insufficient rigidity, abrasion, etc. It is well to It is well to have the armature wires positively driven by the pressure of the parts of the armature frame. When an armature revolves rapidly, the wires, including the binding wires upon armatures using such, stretch and are liable to be more or less displaced unless firmly held. If shaft wires are used passing through the shaft to the collector, special care should be given to ensure a smooth and ample space for placing the same in position, and that dirt be not allowed to settle about the entrance and egress holes. The mechanical design of the commutator includes the matter of proper insulating material between each of the commutator strips and between them and the shaft, the whole being put together in such a way that no piece is liable to work loose.

The electrical design necessitates that there shall not be continuity of the iron of the armature core. The reason for this is that the same force which tends to produce current in the wire would produce current in the iron and heat it if the electrical circuit be complete. Such currents are called Foucault currents. Armature cores are therefore made of iron plates, bands, or wire; plates being used when the active wire is parallel to the shaft, bands when at right angles, and wire being applicable to either case.

(To be continued.)

THE TRENT GAS ENGINE.

Amongst the various gas engines which are coming to the front as motors for driving electric light machinery, the Trent gas engine is one which is worthy of some It

attention.

The engine stands on a solid cast-iron bed-plate. has only one working cylinder and one piston, and the piston being carried at both ends is not liable to wear the cylinder, as is often the case with horizontal engines

The explosion is silent, and as the engine has no cogwheels, no rattling noise is experienced. This of itself is, of course, a great advantage when applied to running dynamos near houses or in a cellar. It is arranged to receive an impulse every revolution, and the running is very even and regular, and is therefore specially adaptable to driving dynamos. It has only a single crank, like that of a steam engine, cut out of solid forged steel, and has no complicated levers or links of any kind.

Amongst the other practical points of advantage, the Trent engine has no slide-valves, and no small parts or sensitive passages. The special point about the construction is the patent explosion-chamber. The explosion takes place outside the cylinder proper, and in the explosion-chamber itself there is no working part. The most intense heat is therefore outside the cylinder, and not on the piston, which therefore requires less lubri cation and wears longer than can be the case with engines having the explosion direct. A great saving is also effected in the lubrication, as there is no burnt oil.

It is a slow-speed engine, working with a low-p -pressure explosive mixture. The initial pressure is only about 100lb. per square inch, against 200lb. or even 250lb. in other gas engines, so that the extreme difference is less, and the engine will "explode" with a gas mixture varying in strength to suit the power required. This, added to the fact of there being an explosion every revolution, makes the running very regular. Quite recently an engine was supplied for lighting the Drill Hall, Derby. During an exhibition of several weeks, although there was only one flywheel on the engine and none on the dynamo, and notwithstanding that there were no resistance coils or accumulators, the incandescent lamps were driven with perfect steadiness, the needle of the voltmeter showing no apparent variation.

As it compresses at a relatively low pressure, the engine is very easy to start, and owing to its special construction the starting is certain. This advantage is considerable in practice. The consumption of gas is exceptionally low, and is diminished by an efficient governor when the work is light. A recent test with indicator showed that a gross power of 10.2 i.h.p., and with the friction brake at the same number of revolutions (174), a useful horse-power of 6.4 e.h.p. This result was obtained with a consumption of 180 cubic feet of gas per hour, being less than 18 cubic feet per i.h.p. This result was with the earlier form, and the recent forms have tested even better than this.

The working parts consist only of the piston and steel valves, all easily accessible, not subject to undue wear, and all exhaust the exhaust valve, only needing the most occasional cleaning. The ignition, controlled by a small positiveacting valve, is absolutely reliable at any speed, and cannot take place prematurely. The exhaust gases escape at low pressure, and do not make any objectionable noise. The handling of the engine is easily learnt by any unskilled

person.

The special patent governor motion cuts off the gas in event of the governor belt breaking, so preventing racing, or if the engine is accidentally stopped and the gas left in, danger from escape of gas is prevented. The very sensitive trip motion keeps the speed extremely even. The engines are made in sizes of 11, 2 (these being vertical), 4, 6, 9, 12, and 25 nominal horse-power. The 25-h.p. engine is a twin engine, having two impulses every revolution, specially adapted for electric lighting. The speeds range from 210 revolutions in the smaller sizes to 150 or 160 in the larger ones. The latter can, however, be run to 180 or 200 revolutions if desired, with proportionate increase of power. The brake horse-power is considerably more than the nominal horse-power. The Trent Gas Engine Company

remaining from the previous explosion, which escape through the valve R), and the mixture is then ignited. The resulting expansion impels the piston outwards. The acquired momentum of the flywheel performs the in-stroke. The Trent Gas Engine Company, whose address is New Basford, Nottingham, supply a complete small electric lighting installation-consisting of 11-h.p. Trent gas engine with bed-plate (no other foundation needed), tank, antifluctuator, bag, and all piping, except from meter and to exhaust, together with compound-wound dynamo, belt, fuses, switches, and wires for one 150-c.p. Sunbeam lamp and 12 16-c.p. incandescent lamps, opal shades-the whole forming a neat and compact installation. One of these small installations is shown running at the Brewers' Exhibition at the Agricultural Hall.

WATT'S ELECTROLYTIC ZINC PROCESS.

The importance of a practical process for the extraction of zinc from its ores by electrolysis has always been fully recognised, and the desire to furnish such a process has been shown by the goodly list of patents which have from time to time been taken out in this and other countries for the treatment of zinc ores by the electrolytic method. It is now well known, however, that none of these processes have been successful when attempts have been made to carry them out, even on a moderate commercial scale. The causes of failure which have hitherto beset the path of the inventor have been many, but the chief difficulty has ever been in the nature and preparation of the electrolyte, and this, as is well known, is the most important factor in any electrolytic process which involves the deposition of a metal from its solution, but more especially so when such metallic solution has been obtained direct from the ore.

In dissolving out the oxide of zinc from calcined blendes, hydrochloric acid presents several advantages, but since chlorine is set free at the anode during the electrolysis of the zinc chloride formed by its agency, this acid may be considered unavailable for the purpose. Sulphuric acid has therefore been the accepted solvent of the zinc oxide, and the zinc sulphate has been repeatedly tried as an electrolyte for the extraction of metal from the ore. The objections to sulphate of zinc as an electrolyte are by this time pretty well known. However, it may be well to recall a few of them to show how unreliable is a solution of this salt for the reduction of the metal by electrolysis, but more especially so when insoluble anodes are employed, as in the extraction of zinc from solutions obtained from the ore: 1. As soon as the electrolyte becomes even moderately acid from the extraction of a portion of its zinc by deposition upon the cathodes, polarisation at once sets in, and the plates become covered with dark patches, the same appearance being usually manifest also at the upper surface of the plate. 2. The deposited metal, instead of assuming the true reguline character, having a perfectly metallic appearance, often occurs in the form of a non-reguline grey powder, which may readily be wiped off the plate with the finger. This granular metal, if allowed to deposit to any appreciable extent, frequently acquires a spongy form of considerable thickness, and of a dark grey colour, in which condition it is quite unsuitable for melting. 3. The zinc, soon after a very moderate thickness of the metal has been deposited upon the cathodes, commences to form in the shape of branching crystalline growths-especially at the corners and edges of the plates-and these so-called "trees" quickly spread out in the direction of the anodes until they finally come in contact with those electrodes, when, as a matter of course, the current is short-circuited, and the further deposition of the metal brought to a standstill. The inconvenience attending crystalline growths of this character cannot well be over-estimated, and it seems tolerably clear that if there were no remedy for such irregularities, that an electrolyte which favoured their formation would be practically useless for the commercial production of zinc by electrolysis.

Having, some years before, obtained some very satisfactory results from solutions of metallic salts prepared from the vegetable acids, it was resolved to ascertain if an

electrolyte of practical utility could be formed by employing a vegetable acid as the solvent for oxide and carbonate of zinc, and for this purpose the cheapest of these, acetic acid, was at once selected for the first trial. The substance first operated upon was an impure form of oxide of zinc known as "flue-dust," which sometimes contains from 2 per cent. to 6 or 8 per cent. of oxide of lead, besides other metallic and earthy impurities. To dissolve out the zinc and lead from the impure oxide, ordinary commercial acetic acid (15 per cent. real acid) was employed, and to a quantity of this acid flue-dust was gradually added, a little at a time, and the mixture well stirred until the acid was neutralised. The whole was then allowed to stand for a few hours, when the clear liquor was run off into a separate vessel; scrap zinc was now thrown into the liquid for the purpose of precipitating the lead held in solution by the acid.

When the whole of the lead had been thrown out of the solution by the zinc, the undissolved portions of the latter metal were removed, and after a few hours' rest the clear liquor was run into the electrolytic tank, and the precipitated lead, after being well washed, was put aside for meiting. The electro-deposition of the zinc was next proceeded with, carbon anodes being employed, and some very good results were obtained, the reduced metal being of very good quality. The E.M.F. required was, however, found to be rather high, and this induced the author to seek an improvement in the direction of diminishing the resistance of the solution. With a full knowledge of the defects inherent to the zinc sulphate solution as an electrolyte, as before explained, when employed per se, and having before obtained some very good results from mixed solutions of metallic salts prepared with mineral and vegetable acids respectively, it was determined to make a series of experiments with a view to improving the zinc sulphate solution so as to make it available as an electrolyte by removing, if possible, its characteristic defects-namely: (1) Its disposition to deposit the zinc in a granular or spongy form; (2) its invariable liability to yield crystalline deposits of a treelike form. In pursuing these experiments, varying proportions of solutions of zinc acetate, citrate, or tartrate, etc., were added to neutral solutions of zinc sulphate, and the compound electrolytes were then tried with a suitable current for obtaining a prompt but not too rapid deposit of zinc, carbon anodes being employed as before. It may be said with truth that the first trials with the compound electrolytes were distinctly, and indeed remarkably, favourable. Instead of the metal assuming the grey, spongy, or granular condition, it was almost white, perfectly reguline, and possessed a fine metallic lustre, and in lieu of the fibrous crystalline deposit sometimes obtained in zinc sulphate solutions, the metal assumed a nodular or botryoidal form of a decidedly solid character, and absolutely free from "treeing.".

Having advanced thus far in the direction of obtaining a suitable electrolyte for the deposition of zinc, it next became a question of selection, and from considerations of economy and practical usefulness, mixed solutions of acetate and sulphate of zinc were taken, about 10 per cent. of the acetate solution being added to about 90 per cent. of the sulphate solution, and the compound liquid was then reduced with varying proportions of water, the density being taken with the hydrometer after each addition, and the solution was electrolysed after each addition of water until the specific gravity of the liquid most suitable for the electrolyte was determined. Having now succeeded in obtaining a solution from which zinc could be deposited in the best possible condition for melting, it next became necessary to see how the compound solution would work when prepared on a larger and more practical scale. For this purpose, a quantity of impure oxide of zinc, containing at least 5 per cent. of lead, was first treated with 15 per cent. acetic acid for the purpose of dissolving out the lead oxide (a portion of zinc oxide, of course, dissolving also), and the resulting acetate solution was then allowed to settle, when the clear liquor was run off as before, and the lead precipitated with scrap zinc. When it was found that all the lead has been thrown down, the clear solution was then transferred to tanks furnished with carbon plates for anodes and plates of sheet zinc for the cathodes. The

current was then switched on and the deposition of the zinc allowed to proceed for some hours, by the end of which time the plates had received a considerable thickness of zinc of a very good colour, and quite free from "treeing." During the electrolytic action there was no evolution of hydrogen at the cathodes, but a slight frothing at the anodes due to the liberation of oxygen at those electrodes. In the trials referred to the current was varied from time to time in order to determine the most economical conditions of working, and it was found that a current of 3.2 amperes per square foot of cathode surface, the E.M.F. per tank being 3:38 volts, gave the most favourable results. Thus 30 tanks, having 312 square feet cathode surface in each = 9,360, would give a deposit of four tons 16cwt. per week of 144 hours. The theoretical deposit of zinc per ampere per hour being taken as 189, the result given was found to be equal to about 95 per cent. of the possible quantity, which, in the deposition of a metal such as zinc, with insoluble plates for the positive electrodes, may be considered a very good result. Moreover, the temperature of the solution at the time these trials were conducted was somewhat low for an electrolytic operation, being only 50deg. F. At a higher temperature, say about 70deg. F., far more economic results would undoubtedly be obtained, as will be well understood. Respecting the density of the solution, many comparative trials were made, and it was found that a specific gravity of about 1130 (water being 1000) yielded the most favourable results. It should also be mentioned that the carbon anode connections were very imperfect, which would naturally tend to increase the resistance of those electrodes, and necessitate a higher E.M.F. than would otherwise be required. To determine the distance at which the electrodes should be placed apart, several trials were made, when it was finally decided that about 2in. apart was a very good working distance, and they were therefore uniformly kept at that distance in all subsequent trials.

Since the foregoing results were obtained, a further series of tests was made, with a view to still further increase the efficiency of the process, when it was found that with a current of 4.2 amperes per square foot of cathode surface, and an E.M.F. of 3.0 volts, the exact theoretical quantity of zinc-18.9 grains per foot per ampere-hour-was deposited, showing (1) that a more suitable current density was used than in the former trials; (2) the temperature of the solution (60deg. F.) being 10deg. higher than when the former trials were conducted, the E.M.F. was sensibly reduced. Respecting the solution obtained from the ore, it was found, after throwing down the lead with scrap zinc-which zinc, by the way, is recovered with the zinc from the ore-that a small quantity of iron had been dissolved by the acids employed, but no trace of this metal, however, appeared to be deposited with the zinc; indeed, this would seem to be a chemical impossibility, for the iron, as soon as it is set free by the action of the current, is at once oxidised by the oxygen liberated at the anode, and deposits at the bottom of the tank as peroxide, and is therefore perfectly harmless so far as the electrolyte is concerned, and cannot deposit with the zinc upon the cathodes. It should be stated that when the deposited zinc was stripped from the plates, melted, and cast into ingots, these, when broken, exhibited a fine crystalline fracture equal to the best commercial spelter.

When treating blende, or sulphide of zinc, by this process the ore is first crushed, ground, and calcined; and in order that the oxide zinc and lead (if any of this metal be present) may be readily dissolved by the acid solvents, the calcined or roasted ore should be reduced to a fine powder. The dissolving of the oxides from the ore. is then conducted as follows: A cylindrical wooden tank, having an agitating arrangement attached for the purpose of well mixing the powdered ore with the acid solvent is provided, and a quantity of 15 per cent. acetic acid is put into this tank, called the "dissolving tank." A calculated proportion of the powdered ore, according to its ascertained percentage of oxides zinc and lead, is now gradually introduced into the dissolving tank, its agitator being previously set in motion, until the entire quantity has been introduced, and agitation

is kept up until the solution is neutral, or nearly so, to litmus paper, which generally occupies about an hour. The vessel is then allowed to rest for about 12 hours, when the clear liquor (acetate of zinc and lead) is run off; water is then pumped in, and the agitator again set in motion for a few minutes to enable the water to wash out a greater portion of the zinc salts from the residual matters. Agita tion is now stopped, and the sediment allowed to deposit, when the clear liquor is again run off and added to the first liquor, Another washing or two may be given if necessary, and these weaker liquors may be used in lieu of water in subsequent operations. The liquors obtained from this first operation are then treated with scrap zinc to throw down any lead that may be present. A quantity of dilute sulphuric acid-about one part acid to six parts of wateris next run into the dissolving tank, the agitator set in motion, and the agitation kept up until the liquor has become neutral, or nearly so, a slight trace of free acid not being very objectionable. The agitator being stopped, the vessel is allowed to rest until the residual gangue has deposited, when the clear zinc sulphate solution is run off as before, and the residuum then washed, the first and second runnings being mixed together as in the first operation. The solution of zinc acetate (deprived of its lead as described) is then to be added to the zinc sulphate solution, and the compound liquid is then ready to be transferred to the tanks in which the metal is to be reduced by electrolysis. When mixing the zinc acetate and sulphate solutions, an hydrometer should be floated in the liquor, and the specific gravity noted from time to time, and, when necessary, the solution may be reduced by adding the requisite proportions of the wash-liquor from the dissolving tank. The solution should stand at specific gravity 1130 or thereabouts.

The compound solution of acetate and sulphate of zinc is put into tanks furnished with plates of carbon, arranged at about 4in. or 44in. apart, each plate having a strip of sheet lead lapped firmly over its upper end, so as to form a good connection between the carbons and the supporting rods. The cathodes may consist of thin plates of Silesian sheet zinc, on which are left two or more equidistant projections, which, being bent in the form of hooks, are used to suspend the plates from the conducting rods to which they are to be connected. The electrodes, as also the baths, are connected in series. In order that the solution, when the current is passing, may be kept in as uniform a condition as possible, a system of circulation must be adopted, by which the partially-exhausted liquor of the electrolytic tanks is allowed constantly to flow out of the tanks into a receiving vessel, and an equivalent quantity of fresh liquor is as constantly supplied to the tanks from a head tank fixed at one end of the series. The partially-exhausted liquors, having now free acid in place of the zinc removed from the solu tion by deposition upon the cathodes, is recuperated, and its free acid neutralised, by being agitated in a tank or vat furnished with a proper agitator, in which is placed a sufficient quantity of powdered ore (previously deprived of its lead, as described, if any be present) and the agitation is maintained until the liquid again becomes as nearly neutral as possible. The liquor, thus restored to its proper condition, is then allowed to settle until quite clear, when it is removed to a store vat, from which the head tank is supplied with zinc liquor for the electrolytic tanks This system being kept up with perfect regularity in all points, the operation proceeds with uniform results. (To be continued.)

THE WIGAN TRAMWAYS.

We are under the impression that while such estimates. as the following possess a certain value, they do not contain the estimates that form the crux of the whole question. The extra initial expense of £5,000 or £10,000 is often not worth five minutes' consideration, providing the working expenses and cost of maintenance are satisfactory. Let us take an example. Suppose a tramline on one system costs £20,000 and on another cost £30,000, and let the earnings be the same whichever system is installed-say, £5,000 a year.

Now suppose the working expenses and the cost of maintenance of the cheapest system to be 75 per cent. of the receipts, and in the other case 50 per cent. The balance for dividend in the former case is £1,250, in the latter £2,500-that is, the one pays 61 per cent., the other 8 per cent. The initial expenses, then, although very important, even when known leave some other knowledge to be desired. Contractors are perhaps not the best people to supply this information, but surely if Wigan is definitely thinking of electricity some information can be had from Blackpool in this important branch of the case, and a suitable allowance made if the system suggested is different from that in actual operation. The following is the information to which we have referred:

Sun Bridge-chambers, Bradford, October 17th, 1891. Mr. John Gee, Wigan. Dear Sir, I have gone into the cost of electricity, and beg to send you some figures for your perusal. They are necessarily rough, but sufficiently accurate for discussion of the question. Electricity will cost more on capital account than steam; but it is for you, the Corporation, and the road authorities to seriously consider the matter of adopting a system which will rid the streets of the engines, and considering the weight of engines (10 tons) the life of the rails will be much longer, and the cost of repairs to pavements will also be considerably reduced thereby. In the event of the Corporation and road authorities deciding, upon some amicable terms, to take over the roads as per Mr. Alderman Ackerley's speech in the Council on 7th inst., a most proper thing for them to do, it is possible they would also elect to do all the work on the roads, such cost to be capitalised and interest paid by you for the outlay, you, however, to be at the cost of keeping the installation in good working order. The cost to you of the power, dynamo, and necessary work at the depots for the generation of the electricity and the equip; ment of the road with cars will be far greater than if the road is re-equipped with steam engines and cars. But I wish you to consider the great opportunity there is in Wigan of adopting a system so noiseless and healthful as compared with steam, and one which has now passed beyond the region of experiment. There are in America (apart from several on the Continent) 140 roads in use on the system I recommend for your adoption. I have visited some of the roads both in America and on the Continent. The first road in England on the system recommended will be opened at Leeds this month, and yesterday I went over to Leeds and saw the chairman of the Tramway Committee of the Leeds Corporation, Mr. Alderman Firth, and the engineer of the line, Mr. Winslow, and arranged that you should the first week in the next month, on some convenient day, invite the members of Mr. Alderman Ackerley's committee and the members of the various committees appointed by the Local Boards of Pemberton, Ince, and Hindley to see the road in working order for themselves. This, I take it, will be desirable on all points, as it is impossible for them to discuss the merits of my proposition without seeing the system in active operation.-I am, dear Sir, yours obediently, JOHN WAUGH. P.S.-As I am not known to any members of your Corporation or local authorities, I have ventured to ask our town clerk, who has known me 20 years, to introduce me to your town clerk, and I send you a copy of such introduction as follows: "[COPY.] Town Clerk's Office, Town Hall, Bradford, 16th October, 1891. My Dear Sir,-I understand that Mr. John Waugh, C.E., of this borough, is in communication with your Town Council and yourself on the subject of tramways at Wigan, and as you will naturally wish to know what Mr. Waugh's experience may be in such matters, I have great pleasure in assuring you that he is thoroughly master of the whole business, whether the tramways be worked by animal power or by steam or electricity, as well as haulage by underground cable. As the engineer for a company here, to whom the Corporation leased an important and very difficult line of tramway on severo gradients, he gave the highest satisfaction both to the Corporation and to the company. Whenever I want a bit of sound, friendly advice, I apply to him and get what is wanted. Only recently I consulted him about a contemplated electricity line, and I know that at St. Helens he converted the tramway undertaking from a dead loss into a successful business. I write this with full knowledge of the responsibility you bear towards your Corporation, and am justified in assuring you that you may safely rely on any advice or assistance you may require from him.-Kind regards, yours truly, W. T. McGOWEN. Arthur Smith, Esq., town clerk, Wigan." Rough estimate for electrical trams-total cost: Engine at Pemberton Depôt, 200 i.h.p. maximum, £800; two boilers, £850; chimney, £250; dynamos, straps, etc., £2,000; six miles of posts at 100 posts to the mile, 50 on each side at £6 each, £3,600 (see note as to wood posts); 600 posts fixing at £1 each, £600; 12 miles of wire, 1,800lb. to the mile, at 8d. per lb., £720 (one wire overhead and one between the lines under pavement); fixing wire overhead

and between rails, £550 (see note re wire between rails); wires and suspenders, insulators, and turnouts, £375; 10 cars, with motors, at £950 each, fitted with electric light, £9,500; four spare cars without motors, £250 each, £1,000; 10 per cent. for Gee, provided he find the power, dynamos, etc., in sheds, and for contingencies, £2,024-total £22,269. Estimated cost to Mr. John road equipment, rolling-stock, etc. Stationary engine at Pemberton Depôt, 200 i.h.p. maximum, £800; two boilers and chimney at Pemberton Depôt, £1,100 (one boiler will be sufficient for power required); dynamo, straps, etc., £2,000; 10 cars, with motors, at £950 each, fitted with electric light, £9,500; four spare cars, without motors, £250 each, £1,000; 10 per cent. for contingencies, £1,415-total £15,815. Note.-As to cars on the electrical system, there would be no upper saloon. On the question of stability, I am of opinion that the cars with such upper saloons, on a four-wheel base and a 3ft. 6in. gauge, have not a sufficient margin in the interests of public safety. Estimate of costs in roads, provided local authorities find capital for all in the streets: Six miles of posts at 100 posts to the mile, 50 on each side at £6 each, £3,600 (see note as to wood posts); 600 posts at £1 each, £600; 12 miles of wire, 1,8001b. to the mile at 8d. per lb., £720 (one wire overhead and one between the lines under pavement); fixing wire overhead and between rails, £550 (see note re wire between rails); cross wires and suspenders, insulators, and turnouts, £375; total, £5,645; 10 per cent. for contingencies, £584; total, £6,429. Notes.-Length of road: A little over five miles only, so that the estimate is in this regard in excess of requirements. Wood posts: 10s. to 15s. each, only making a great difference in cost. Wire between rails: If this was done on the relaying of the track, the cost would be very much reduced. Steam engines, etc.-Equipment of road: Twelve engines at £800 each, £9,600; 12 cars at £280 each, £3,360; 10 per cent. for contingencies, £1,296; total, £14,256. Summary and comparison: Electrical installation and equipment, £22,269; steam engines and cars, annum). This will be more than compensated for in the £14,256; difference (capital) £8,013 (5 per cent. on = £400 per difference of cost of working between steam and electricity. Less cost of fuel, wear and tear, shop wages, drivers, and conductors. N.B.-Provided electricity is adopted the cost of putting the rails into order will be considerably less than in steam, as apart from the nuisance of the engines, chey weigh 10 tons, and our weight would not exceed four tons, a great

difference in the matter of life of rails, and wear and tear of same, and repairs to pavement.

As at present arranged there are one principal and three secondary stations, the central one being very close to the gas undertakings under one general management, and also to allow of works. This method has been adopted so as to combine the two a plentiful supply of coal to be at hand. The sub-stations are situated at a distance of about one and a half miles from the central station, the first being in Bleichstrasse, the second in the Bade-Anstalt, and the third in Karlsstrasse. The current from the generating dynamos is used partly to charge the secondary batteries in the sub-stations, and partly to feed the distributing mains simultaneously with the accumulators. The latter receive the current which is in excess of temporary demand when the machines are running at normal load, and in the hours of minimum demand they alone suffice, whilst when the consumption of current is the greatest, both the batteries and the dynamos work in conjunction. By this means it is claimed that the dynamos run at regular load during all working hours.

The central station contains three water-tube boilers made by the Hohenzollern Company, of Düsseldorf, one being as reserve; each has a beating surface of 150 square metres. The two steam engines, which will shortly be supplemented by a third, were supplied by the Saxon Engineering Works, of Chemnitz; they are of the horizontal type with tandem cylinders, work at 120lb., and are of 300 normal horse-power. Each engine is direct coupled to a Schuckert dynamo giving 1,000 amperes at 350 volts. In addition to the mains connecting the central with the sub-stations, and which were furnished by Messrs. Felten and Guilleaume, of signals and telegraph wires. Mulheim-on-the-Rhine, communication is possible by means of Two of the sub-stations contain small batteries, whilst in the third, near the Tonhalle, two sets of 140 cells, each placed in parallel, and having a total output of 1,000 amperes, are arranged. These storage batteries were provided by the Accumulator Works Company, Limited, of Hagen, who have undertaken to maintain them for 10 years. A