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shape of the wick. The electric terminals carry. cross-section, the rotating discs h and j and their
ing the platinum wire are attached to a single or flanges are not required, as the wick holder
double disc, soldered to a flattened tube, which would revolve in a round extinguisher tube,
acts as an extinguisher, and as the wick with its which would now be stationary, and therefore
flattened tube passes through this disc and the terminal e, instead of being insulated in the
extinguisher, it is necessary when screwing and manner described for the flat wick, would simply
unscrewing the bottom of the lamp into its posi-be insulated directly through the following up
tion, that the disc and extinguisher should be ring i on to the disc m with its flange n.
capable of revolving in either direction. To
permit this to be done, the disc carrying the
terminals rests upon or is supported by a fixed
part of the lamp. When the wick is round in
cross-section it is not necessary for the discs to

MODEL LOCOMOTIVE-MAKING.

XVIII,

ET one more-a very elementary-stage in

reason of the port d coming over the blank space between a and b. Momentum will carry the pin e past f, and thrust the piston backwards, and port d beginning to come over b will allow the steam to exhaust. Thus there is no steam at all admitted above the piston, but the engine depends for its power entirely upon that. admitted through the port d, and is therefore unable to overcome any very appreciable amount of resist

ance.

Cylinders of this toy-like type are not usually cast. They are made of brass tube, with ends soldered on.

revolve, as the wick-holder would revolve in the Model Locomotive construction, and I will stand, say, from 25lb. to 30lb. pressure, and

extinguisher tube. The terminals are con-
nected together by a horse-shoe shaped form of pass on to the long-promised Tenders. In this
platinum looped tube, within which is a sup- and the next article I will briefly describe a
porting wire, insulated by enamel or other mate-model fitted with oscillating cylinders. There
rial. One of these terminals is connected by an will be many resemblances between this and the
insulated screw with an insulated flanged disc, previous one. I suppose the same wheels to be
the other terminal forming part of the lamp used, and, with slight alterations, the same
circuit. At the side of the lamp is an insulated framing and spirit-lamp. The boiler will be of
horizontal plunger working in a socket, which the same size, but alternative, and, as I think,
when pressed home, makes contact with the rather improved methods of construction will be
flanged disc and the battery itself, thus forming shown, and a simpler and equally efficient steam-
a complete circuit between the battery, the pipe arrangement. These will be illustrated in
lamp, and the terminals thereof, a spiral spring the next article. In the present I will confine
being employed to withdraw the plunger from my remarks to the oscillating cylinders.
making contact with the flanged disc. The The only thing to be said in favour of these
fusion of the horse-shoe looped tube is prevented oscillating cylinders is that they are easily fitted
by the insulated platinum wire passing through up. They are not models of the actual engines
it, so that when the current is established, the which are denoted by the same name. They are
outside platinum horse-shoe loop becomes in-not even satisfactory as a rule in working. So
candescent, whilst the insulated core remains
comparatively cool for a certain time, and so
supports the heated platinum tube.

little steam can get into the cylinders that, to
dignify a small matter, they exert very little
tractive force, and often fail to drive their engines
along. Tiny stationary engines with oscillating
cylinders will whizz round rapidly enough; but
the weight of the oscillating-cylinder locomotive
will sometimes put so much work upon the
engines that they refuse to move at all; or, if
they move, it is only in a fitful, uncertain
manner. Especially is this the case with what
is called the single-action engine that is, the
one in which the steam enters only at the bottom
end of the cylinder, and not at the other end
at all. Such a cylinder is shown in Fig. 78.

But with a strongly-made boiler, sufficient to double-action cylinders of good capacity, and well fitted, a good workable locomotive can be made with oscillating cylinders. Simplicity of construction is a recommendation to beginners, and an oscillating-cylinder engine affords good preliminary practice. In the construction of the simplest slide-valve engine, some neat and accurate workmanship is required; but in oscillating engines there is really little that a mere lad cannot carry through. I think, therefore, these are good and sufficient reasons why an example of that type should not be omitted

from this series.

Fig. 79 shows the engines in plan, the lefthand cylinder being a sectional view; Fig. 80 the same, in cross section; and Fig. 81 the cylinderface and the fitting that fulfils the function of steam-chest and exhaust, usually termed the steam block.

There is no connecting-rod, of course; but the piston-rod goes direct to the driving-wheel, and as it is necessary that the steam openings a a a should be for as long a period as possible over the steam-way d, the cylinders are brought as close as convenient to the driving-wheel to give a goodly amount of angular movement. They, therefore, occupy a position 24in. nearer to the driving-wheel than those in the last example, and the leading wheels are in consequence moved 1ğin. nearer to the front of the engine. This necessitates a corresponding alteration in the pattern of the framing, and gives, the engine a somewhat amateurish appearance but that cannot be helped.

a

The loose bottom C in the Fig. is provided with a lid a, kept in position by the screwed nut or disc b. Rising from the lid a is a flattened or oval tube c, the inside of which corresponds to the thickness and width of the wick d. Within the lamp is a following ring i screwed into position for holding up the glass ring B by pegs or studs r, which ring i carries two discs h and j, soldered to an extinguisher tube . The tube c rising from the loose bottom C, together with the wick, is inserted up through the extinguisher tube 1, and as the loose bottom has to be screwed In this figure, A is a block of metal fastened in and out of its position, it follows that in con- to the framing, and its function is to convey the sequence of the extinguisher tube being oval, live steam into the cylinder, and carry the exWe suppose, then, these alterat elons in framing, the extinguisher must revolve with the loose hausting steam away. It is pierced with two and positions of wheels are made, and the busibottom in either direction. For this purpose holes-a the steam inlet, and 6 the exhaust out- ness of making and fitting the criylinders to have the loose discs h and ride or oscillate upon a let. The lines encircling these holes represent commenced. The pattern of the cylinder will, shoulder formed on the ring i. The terminals hollow depressions cut in the face of the block as regards bore and length, be exactly like that e and fare attached to the top disc h, the latter to prolong the period for admission and exhaus-shown in the previous engine. terminal ƒ forming part of the lamp circuit. The tion; these are not, however, always cut. Often bolting to the foot-plate, and former terminal e is insulated from the two discs there is no through-hole for the exhaust, but through which the port faces by any suitable insulating material. The only a groove cut right out to the edge of the omitted, and a circular facing terminal e is also attached, by means of an insu-block, and the steam then escapes from between is shown at A in Figs. 79-81. The cylinder is lated screw, to an insulated piece of brass the two faces. At e there is a pin upon which pivoted by the pin B, to the block C, which is fitting on the lower disc j, which does not touch the cylinder B is pivoted, the pin c being tapped fastened to the framing with a couple of screws. the lower portion of the extinguisher tube l, nor into the cylinder face. By means of the pin, The pin B is tapped into the centre of the the lower portion of the following ring i. On the cylinder is held against the face of A with a circular disc A on the cylinder, and screwed at the underside of ring i is another insulation, and little nut and spring, the spring permitting the opposite end to take a milloted-headed nut, D, on the underside of that a disc m having a of freedom of movement when the parts become which serves to pull the cylind insulated screws. The insulated piece of brass q cylinder face, the radius from e to d being minimising escape of steam fi rides when revolving upon the disc m. To light the same as that from C to the lamp, the horizontal insulated piston is pressed home by a suitable device on the top of a battery, making contact against the flange n whereby a complete circuit is established when the body of the lamp is placed upon the other pole of the battery. When using wick round in

But the foot for the square block the are cut will be substituted.

Els

att

This

flange n, such disc being kept in position by hot. At d there is a hole drilled into the face of the steam-block C, cher-face against the

a

ee 180

preventing or

and b. faces. The interposition of thelarom between those

As the cylinder is shown on the right-hand of
Fig. 78, the steam is entering from a into b, and
pushing the piston along in the direction of the
arrow for the forward running of the engine.
As the crank-pin e goes round, and nears the
dead point f, the steam will become shut off by

lee spring E imparts an elastic character to this tension, and thus allows much freedom of oscillating movement to the cylinder. The construction and action are as follows:

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The cylinder face A is pierced with two ports, a, a, a, communicating w ith drille passages,

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CROSS SECTIONS

is the front view facing towards the cylinder, having the steam and exhaust openings b, c, and the steam and exhaust channels d and e. These

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of its own, and refers, as everybody knows, to a very important question connected with the currency. We might apply the term with equal accuracy to a new development in the methods of transmitting electrical energy which is beginning to attract the attention of practical men; but it might lead to some confusion of ideas, and in all scientific matters lucidity should be a sine qua non. Hitherto, in transmitting electricity through metallic conductors, the use of a single metal has alone been resorted to at all extensively, and experience has shown that of all the commoner metals copper presents the greatest advantages. If we take the conductivity of mercury to be unity, then, according to Matthiessen, we have the following values:

Silver Copper Gold Zinc Platinum

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65.64 61.70

47.92

17.52

6.46

channels are grooves cut in the face of the block
at the same radius as the port-holes a, aa in the
cylinder face. The live steam passes from the
steam-pipe bb through the opening b in the
steam-block, and occupies the groove d. With
the axis of the cylinder along the line E, the
porta in the cylinder-face will be open to the
groove d. Steam will enter a, and drive the
piston and rod along the line E in the direction
of the arrow, and move the crank-pin and wheel
in the direction of the curved arrow. The posi- the following relative values:-
tion E of the axis of the cylinder represents the
widest possible opening to steam; but steam had
entered the port a some time earlier, and will
continue to enter some while longer. As the
piston moves round, and the crank-pin ap-
proaches dead centres, the port a comes partly
opposite the narrow bar f, and the supply of
steam is diminished; but it is not wholly cut-off
until the instant when dead centres is reached.
Immediately this point is passed the port a

Or, according to another authority, if the conductivity of silver be taken at 100, then we have

Silver Copper Gold..

Soft Iron.. Lead Mercury

100

96

74

16

8

1.6

Silver is placed outside industrial application by reason of its costliness, etc., and hence copper has been uniformly adopted.

But copper, though excellent for conducting

free passage of the current, is by no means perfect it is deficient in what may be termed mechanical resistance, and is somewhat easily stretched. A rod of copper whose transverse section is one square centimètre, when stretched with a force of one degree gives an extension equal to of the whole length (Un1,050,000,000 × 981 win and Wertheim), and it has not the tenacity iron, for

1

It is only possible to obtain a great mechanica resistance by incorporating with the copper some foreign metals or substances which, while increasing its strength, seriously affects its high electrical conductivity. During the past four years a great deal of research has been prosecuted with a view to discovering some alloy of copper which shall successfully combine these desirable qualities of high mechanical resistance and low electrical resistance, so that it shall, when drawn into wire, meet the requirements of every case in which such conductors may be used, and be at the same time reasonably cheap.

proposed, few of them have received any attenAlthough a great many of these alloys have been tion outside the experimental laboratory. Those which have been more especially regarded with favour are the phosphoric and silicious" bronzes." Copper will combine with phosphorus directly under the influence of heat, or when the metal is heated with bone-earth and charcoal, yielding a product which is grey, approaching to whitness in colour, and is very hard and brittle at ordinary temperatures. If, however, the proportion of phosphorus present be kept sufficiently low, the hardness and fusibility of the copper are increased, and if the proportions be copper, 1,000 parts; phosphorus, 5 parts, the tenacity is wonderfully improved.

The improving influence of phosphorus is seen in the so-called "phosphor-bronze," an alloy of copper and tin containing traces of this nonmetallic element; specimens submitted to testing have withstood a tensile strain greatly in excess

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of that afforded by copper or bronze, and ranging | as high as 74,966lb., that is to say, over 33 tons per square inch. And these figures have been greatly exceeded after "wire-drawing." In this case the elasticity has also been greatly improved. There was a proposal a few years ago to utilise phosphor-bronze for overhead wires, as it was asserted that when, through accident, such wires became severed they would not fall, and thus become a source of great danger, but would at once coil up and remain out of danger of doing any damage. Silicon has a somewhat similar effect upon the properties of copper when combined

with it.

Now, although these silicious and phosphoric "bronzes" satisfied to some extent the exigencies of re conductors, certain inconveniences attached to their use, combined with their high price, have prevented them from being universally adopted, and one after another they have been "dropped."

An entirely novel proposal has recently been made by a French engineer-Mons. Edouard Martin-which, it is alleged, is likely to become rapidly and widely adopted, since it refers to a really practical solution of the problem of wire conductors, and is not merely "another new

scientific nostrum."

Mons. Martin has devised a compound or bimetallic wire, which consists of a steel core sheathed in copper. This, it is said, combines the desirable advantage of lightness, high mechanical resistance, and cheapness, with a sufficiently low resistance to current for all ordinary practical purposes.

The annexed figure will give our readers at once a clear idea of this invention, which, like so many other "good things," appears to be extremely simple, and one is led to wonder that it has not been adopted long ago. In the figure two enlarged sections of Mons. Martin's wire are shown-one a vertical longitudinal section, and the other a vertical transverse section.

In the longitudinal section AAAA is the copper sheathing, and B is the steel core. In the transverse section these different metals are respectively shown at A and B. The diameter (a) of the whole wire is 18ths of a millimètre, and the diameter (bb) of the steel core is 13ths of

milliméter.

The resistance to elongation of the compound conductor varies according to its diameter, but it is always superior to that of steel alone. This appears rather astonishing, but the fact has been proved most emphatically by severe test experiments.

The electrical conductivity of the compound wire, referred to that of pure copper, has been determined to be about 60 per cent., that is

Conductivity.
60
100

A

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This tabulation suffices to show at a glance
what are the advantages presented by the new
bi-metallic wire-viz., economy and lightness,
combined with good mechanical resistance and
sufficient electrical conductivity.

mercial scale by a patened process by Mons.
These wires are being manufactured on a com-
Martin, at his works at Joinville-le-Pont, where
specimens are drawn varying in diameter from
a tenth of a millimètre to upwards of a centi-
mètre, the proportion of the iron and steel being
determined by the value of the conductivity
required for any given purpose. There is one
objection which naturally presents itself to one's
efficients of expansion, as is seen in the following
mind: copper and steel possess different co-

table.

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Upon this very principle of the difference in the
coefficient expansion of metals Breguet founded his
well-known metallic thermometer, which all our
readers are probably acquainted with. One might,
therefore, naturally suppose that when the bi-
metallic conductors are subjected to varying tem-
peratures, some disturbance would arise owing to
the inequality of the expansion of copper and
steel. No doubt some action does take place,
but in actual practice, which is the important
consideration, no disadvantages have been found
to arise.

Dr. Laisant proposes to make some exact
determination with regard to the behaviour of the
compound wire under variation of temperature;
but considering the results which have been
obtained in practice, it is not anticipated that
they will bear any influence of value upon the
industrial applications of the new conductor,
though such quantitative experiments will possess
a certain interest from a scientific point of view.
If a further word is necessary to establish the
practical importance of this discovery, it is
sufficient to state that the Administration des
Télégraphs in France and several foreign govern-
ments have already placed large orders with
Mons. Martin.
J. T. N.

machine in a remote country village in a crude form as early as 1834, came to New York in February, 1837, bringing with him some of the exhibition, by himself and Ransom Cook, with a machinery which had been made for the purpose of view to enlisting capital to build a larger motor. During the season of 1837 he occupied rooms in the city, where he exhibited models of his motor and various other electrical inventions. Articles were published in the newspapers of the day, and his exhibitions were attended by a great number of people. In letters written about that time, Davenport mentioned that one of the most frequent visitors was Prof. Morse.

With the history of Prof. Morse and his invention of the telegraph the world is quite familiar. With the history of Davenport and of the invention of his electric motor-as I soon discovered in endeavouring to obtain information about it myselfRind out more about the matter. In this underscarcely anything was known. This difficulty ultimately led me to interest myself in trying to than one can reasonably expect to be, in attempting taking, I was fortunately very much more successful to resuscitate the history of an invention which has lain unknown for the best half of a century.

In pursuing my investigations into the history of

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Davenport's work, I was fortunate enough to find that several of his original models were still in existence. One of these models, a circular railway 24ft. in diameter with a locomotive travelling on it, similar to the one which we have here to-night, but very much more finely finished, I was able to satisfy myself by contemporaneous evidence was built in 1837. The one which is before you was found in the cabinet of the Female Seminary in Troy, formerly Miss Willard's. The records of the institution show that it was purchased in 1840; but it evidently must have been built by Davenport himself prior to the more finely-finished model of which I have just spoken, which was constructed in 1836-7 with the assistance of Mr. Ransom Cook, of Saramechanic. I think there is no doubt that the model a finished toga, a very ingenious person and before us was built in the early part of 1837, and possibly as early as 1836. Fortunately it is, as you Pure copper see, in a very good state of preservation. I have Martin's conductor had it mounted to-night with the same battery that was found with it-a three-cell Grove battery of For the sake of fixing our ideas in comparing pint cups, and I think we shall find that it is in the new conductor with ordinary copper contolerably fair running order. (The model was set ductors, let us consider them as applied, say, to in motion.) It does not go quite 120 miles an hour, telephone work. A telephone wire of diameter has a fixed field-magnet below, and a revolving but it goes! This locomotive, you will observe, 1.5 millimètre, and made of pure copper, will armature above, which is reversed twice in possess a very convenient conductivity, but will not possess sufficient mechanical resistance to every revolution. So far as I am able to discover, enable it to stand all the strain which it might there is a combination found in every practical motor to-day, which Davenport was the first reasonably be expected to have to contend with. Now, to obtain the same conducting power, one DAVENPORT'S ELECTRIC RAILWAY. to make known and to use in 1834. The motor is connected to the driving action by bevel gear. of Martin's bi-metallic wires need only possess a THE following account of the electric railway The field-magnet and armature in the model before diameter of 1.9 millimètre, yet it will have a T invented by Thomas Day the electric railway The field-magnet and armature in the mor model of mechanical resistance which will be equal to all U.S.A., is extracted from a paper read by Mr. 1837 of which I spoke, they are connected in shant. ordinary emergencies. F. L. Pope before the American Institute of Elec- Among other models of Davenport was one having Dr. A. Laisant, who has made careful experi-trical Engineers:-The year 1837 marked a very a horse-shoe field-magnet and four-pole armature ments with these bi-metallic conductors, states important era in the history of the industrial de- with curved pole-pieces, which is really quite an that, to enable a copper wire to stand all the velopment of electricity. During that year two of advanced type of motor. That was also built in ordinary strains which it is likely to meet with the most extraordinary inventions of the present 1837. Altogether, Davenport, between 1834 and of different patterns and when in use, a minimum diameter of 2.5 milli- century made their advent in this city-the electric 1840, built over 100 motors mètres would be necessary. any two of them alike. telegraph of Prof. Samuel F. B. Morse, and the of varying sizes, scarcel Such a thickness electric motor of Thomas Davenport. The motor I discovered also, quite to my surprise, that he was would mean a weight of 43.700 kilogrammes per came first. Davenport, a self-taught Vermont undoubtedly the first to make use of the solenoid kilomètre, and it would cost, according to the blacksmith, who had invented and constructed his with a movable core a a means of moving machinery

10

of any kind. He built in 1839 quite a large motor call-bells. In the cover of the box is an induction up-keep for the same time being £10, whereas operating on that principle, which from the best coil, the primary wire of which and the electrodes system B wasted 3,000 units at a cost of up-keep description I have been able to find of it must have of the transmitter are in the circuit of the battery, of £3, B was slightly better than A, because approached 1H.P. He set that up at 42, Stanton-one terminal of the secondary wire connecting 3000: 1000:: 300 to 333. It was difficult to apply street, in New York; attached a printing press to it, through the hinge of the box with the ground wire, the method of comparison to the systems now in and started to publish the pioneer electrical journal and the other terminal being connected electrically use, as the cost of up-keep was not yet known with of America-a small weekly paper called The with one of the binding-posts on the top of the box. sufficient accuracy. The author's opinion was that Electro-Magnet and Mechanics Intelligencer, printed In one side of the box is pivoted an angled lever whenever underground mains consisted of continuby electrical power. Through the kindness of Mr. forming a support for the receiver, the inner arm ously insulated cables, the sum required for up-keep Davenport's son, Rev. Willard G. Davenport, I of the lever being connected with a spiral spring, would be not less that 4 per cent. of the original have the pleasure, on his behalf, of presenting to electrically connected through a stud with one ter- cost, and was not likely to exceed 7 per cent. the American Institute of Electrical Engineers two minal of the induction coil, while in the path of the When, however, the underground mains took the copies of that paper. These, so far as is known, inner arm of the lever is a contact-point, electric- form of bare copper conductors with glass or porare the only editions ever published: they are ally connected with the transmitter. One terminal celain insulators, the cost of up-keep might be as number one and number two. This was in 1840. of the magnet of the polarised bell is connected low as from 1 to 2 per cent. In this connection I have received within a day or two an interesting with the ground wire, and the other terminal is the distribution system of the Kensington and letter from Mr. H. S. Davenport, a nephew of connected electrically with one terminal of the Knightsbridge Company was described, and referThomas Davenport, still living in Vermont at an magneto-machine, the remaining terminal of which ence was made to the systems of supply for St. advanced age, who, as a boy, was with him a great is connected with the line wire. In using this tele- James's and Pall Mall, Westminster, Notting Hill, deal, and in that way became quite familiar with phone, sounds uttered in the mouthpiece of the and for the St. Pancras Vestry, also that in use at his work. I will take the liberty of reading extracts transmitter, causing the diaphragm to vibrate, vary Birmingham. which give some idea of the manner of man Mr. the contact of the annular carbon electrodes and Davenport was. He says: the cylindrical electrode, and correspondingly vary the current in the circuit. The electrodes are made of binoxide of manganese, graphite, tar, sulphur, and water, formed in moulds and subjected to a strong pressure, the mass then being heated to a high temperature, in a manner similar to that followed in vulcanising rubber.

"Many of his models never left his shop, and were but little known even at the time of their construction. They were only made to show to how many uses the power could be applied, and also to work from on a larger scale, if he could get pecuniary aid to do so. The different models which interested me most, at the several times I was in his shop, were a trip-hammer, a turning lathe, and a machine for doubling, twisting, and reeling cotton or silk, all at the same time. A circular frame fitted with two intersecting tracks, on which

four miniature cork images glided around, he called

his 'puppet-show.' He was naturally of a retiring disposition, but when waked up was very strong in argument. His two favourite subjects were nature and electro-magnetism. He considered magnetism the most important element in the creation of the universe, and thought it would be in its destruction. Magnetism kept the heavenly bodies in their places, and if that failed everything would be turned to chaos. He could see in every rock of the earth the battery of which it was composed. So also in the animal kingdom, the bones, muscles, and blood constituted a complete battery, which exercised a repulsive or attractive force with respect to another organism of the same kind."

NORIEGA'S TELEPHONE. THE telephone patented in the United States by capable of transmitting a large volume of sound over long distances. The transmitter, which is said to be not liable to derangement, is shown in Fig. 2. It has a diaphragm inclosed in an elastic

THE COST OF ELECTRIC ENERGY.

A Engineers on Tuesday, 7th April, the paper
the meeting of the Institute of Civil

read was on "The Cost of the Generation and
Distribution of Electrical Energy," by Mr. R. E. B.
Crompton, M.Inst.C.E.

The author had found difficulty in obtaining accurate accounts of the cost of distribution by the alternating-transformer system, but all the published accounts had shown that the total net cost per unit was greatly in excess of that of the lowpressure system. The author had under his charge a plant of generating and distributing machinery on the alternating-transformer system for the public lighting of Chelmsford, a small private demand existing in addition. In this case the machinery was worked for long periods at a high load-factor, so that the cost of generating was exceptionally low, and as the load in the transformers was perthem as to be worked continuously at their maxifectly regular, it had been possible to so proportion mum efficiency. A table showed the load-factors for this station for the months of August and December, 1890, and a 24 hours' load-diagram, taken on the 20th of January, 1891, was exhibited. The annual load-factor was found to be 31.0, and the pounds of coal per unit generated, 8.88; the pounds of coal per unit delivered, 10.70, hence the efficiency reached 83 per cent. But this was an extremely favourable example, and an alternatingtransformer installation in a medium-sized private house in the Kensington district, tested by Prof. Ayrton, was found to have a mean annual efficiency Part I-Cost of Generation.-With the high of only 53 per cent. The remedy for this defect in efficiency of 96 per cent, which was now attainable the alternating system consisted in what had been in dynamos, the cost of the electrical energy ought called "banking" the transformers. This meant only to be a small fraction in excess of that of a that a district to be supplied with electricity should corresponding amount of mechanical energy. The be laid with a low-pressure network, in all respects wide difference between the calculated amount and similar to that provided for the direct low-pressure the figures attained in practice were considered. system; but in place of the feeders, and at the material, were connected to and up-keep-were influenced chiefly by the "load-network, a fireproof and incombustible chamber factor," the design and arrangement of the plant, and the local cost of material and labour.

Machinery for the supply and distribution of electrical energy came under two heads, namely, the generating-plant, comprising boilers, steam dynamos and switching-apparatus, and the distributing-plant, consisting of a network of conductors, supplemented in some cases by accumulators, and in other cases by transforming-apparatus to change energy from high-pressure to lowpressure.

The author had given the name of load-factor to the relation which the actual output of any given plant bore to what would be its output if it were worked continuously at the full load. In order to compare the relative economy of fuel, water, or other material used in generating electrical energy, he had fixed on a consumption of 25lb. of water and 24lb. of Welsh coal per unit generated as a standard which might be reached in the future, although nothing approaching those figures had yet been attained in practice.

should be formed under the surface of the roadway. In this a number of transformers of graduated sizes were arranged, with the high-pressure maing connected to them, so that the transformers might be switched into action automatically as required; that was to say, during the hours of light load the smallest only would be in action, the others being automatically added as the demand increased.

Summarising his experience, the author endeavoured to show :

electrical energy on the scale at which it was now 1. The actual cost of generating and distributing produced, and with the machinery that was already installed.

2. The direction in which improvements might be introduced to secure greater economy.

3. The important effect of a variable load-factor, which might be almost entirely eliminated from the cost-sheets of those who desired to employ electrical energy continuously.

4. That the losses on distribution in low-pressure supply were already so low that further improvement could not be expected.

5. That the existing systems of alternating supply would have to be greatly modified if they were to be used in residential neighbourhoods having low load-factors.

AN EFFICIENT PLATING DYNAMO.*
HE armature for plating has but a single layer

He then proceeded to describe the electricalsupply stations from which the data for the paper had been obtained, namely, the Kensington and Knightsbridge Electric Lighting Company, and the St. James's and Pall Mall Electric Lighting Company. The load-factor of these stations varied from the exceedingly low figure of 2.5 for the Kensington Station in the month of August to 41.5 on one occasion, which was the best loadfactor of the St. James's and Pall Mall Company's Station, and showed how these varying loadfactors affected the cost of production. It was pointed out that a limited use of storage-plant could reduce the consumption of fuel, &c., and shown by a diagram that the proportion of acsumulators should be about 20 per cent., or 1-5th of band, annular carbon electrodes being placed upon the whole generating-plant. The author recomscrews passed through the diaphragm, one of these mended a return to the older type of internallyelectrodes being movable upon the screws, while fired boilers; the chief cause of the small evaporathe other is fixed, and vibrates with the screws as tion, in low load-factor stations, was the loss of T of wire, with two convolutions to each layer they are moved back and forth by the diaphragm. heat incurred in getting up steam in several To facilitate winding, two parallel wires, No. 10 B. A cylindrical carbon block is supported by a metallic boilers for only short periods every evening; and S. gauge, are used in each coil instead of using stud to project loosely within the annular electrodes Several types of boilers which had been found a single larger wire. Fig. 1 shows the armature towards the diaphragm, the rear end of the stud to have special advantages were described, complete, and Fig. 2 shows the armature core in having a threaded engagement with an insulating one important consideration being that in piece in the back of the diaphragm cell. One branch electric-light stations the space from front to section with the dimensions marked on. It consists of an iron spool filled with No. 18 or of a double conducting cord is connected with one back was frequently limited, so that a boiler No. 20 very soft iron wire, either rusted or varnished of the screws through the diaphragm, and the other which could be built up to a height of from 14 to to prevent Foucault currents. branch is connected with the stud. In the receiver, 16ft. offered several advantages. shown in Fig. 3, the mouthpiece has a laminated diaphragm formed of a number of thin sheets of energy was made up of that of the up-keep of the iron. The poles of a polarised magnet are inserted distributing plant and of the percentage of the in the diaphragm cell to within a short distance of energy which was lost by the fall of pressure in the diaphragm, and the bobbins attached to the the conductors. It followed that the merit of poles of the magnet are connected in series and their competing systems was inversely as the cost of terminals connected with the binding posts projecting generating the units so wasted divided by the upfrom the cell. Within the box, shown in Fig. 1, is keep of the conductors. For instance, if in disa polarised vibrating bell of the usual description, tributing 20,000 units to a given distance system, and a magneto electric machine for operating the! A wasted 1,000 units in a given time, the cost of

Distribution.-The cost of distributing electrical

The heads of the spool are provided with 20 radial slots in which are inserted the small wedges forming the coils are each about 20in. long. The a, separating the coils of the armature. The wires winding is according to the Froelich method. Coil 1 (consisting of two parallel wires as described) is placed entirely upon one side of a diametrical line of the armature, and begins and ends on the

By GEо. M. HOPKINS, in the Scientific American Supplement.

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