London and North-Western and the Midland Railways. The Birmingham and Warwick Canal forms one boundary of this plot. The fuel to be used under the boilers is gas obtained from Wilson's eight-hundredweight producers. Eighteen of Lane's water-tube boilers will supply six engines to produce the 6000 horse-power aimed at at first Air is admitted to the furnaces through gridiron sliding shutters, by means of which the supply is hand-regulated. It mixes with the gas in a mixing-chamber immediately below the front end of the furnace. The roof of this mixing-chamber is an arch of perforated bricks, and these bricks becoming highly heated the mixed air and gas is raised to a high temperature before being ignited. No special means have so far been considered necessary to prevent risk of lighting back into the mixing-chamber. The production of gas in the producers is controlled by the steam jet blown in at the foot of each. The steam for these jets is supplied from a special donkey boiler. The whole of the steam jets are throttled down by the action of a governor that runs, so to speak, in equilibrium with the air-pressure in the mains. The engine drives a small air pump, which forces air into one end of a small cylinder, to the other end of which the air from the mains is admitted. If the pressure rises in the mains above standard, the piston of this cylinder is moved, and this movement is communicated by suitable gearing to the throttle-valve regulating the steam jet to the producers. The production of gas, and therefore the production of heat by its combustion under the boilers, are thus automatically regulated in accordance with the requirements, so that the airpressure in the mains is prevented from varying outside certain narrow limits. In connection with this part of the scheme we may point out that it seems to be a mistake not to throttle the entrance-areas for the air to the furnaces automatically and simultaneously with the regulation of the gas supply. The chief advantage in using gas instead of solid fuel lies certainly in the power of obtaining perfect combustion by thorough admixture and careful proportioning of air to fuel. This advantage is sacrificed if the air supply is not diminished and increased simultaneously with, and in the same proportion as, that of gas. We suspect also that it will be found desirable not to rely solely on the throttling of the steam blast as at present intended; the more direct and rapid action of a throttlevalve between the producer and the boiler-furnace will be highly advantageous, if not necessary. By means of simple mechanical relays, actuated either by the steam or by the compressed air, there can be no difficulty in controlling these three sets of throttle-valves by the action of a single governor.

The steam-pressure is to be 160 pounds per square inch. Each set of three boilers supplies an engine of 1000 horse-power. The engine is of the triple-expansion type; the high-, intermediate, and low-pressure cylinders having the diameters 20, 30, and 49 inches, and a common stroke of 48 inches. The areas of the three pistons are thus in the ratios 1, 24, and 6. The cranks are at 120° to each other. The high-pressure and intermediate cylinders are steam-jacketed at the sides. The low-pressure cylinder is not jacketed, but a novel arrangement of steam-jacketing its piston is adopted. The piston is hollow, and steam is led into its interior by a tube which is parallel to the piston rod, and moves to and fro through a stuffing gland in the cylinder cover, projecting into a larger tube screwed on the gland and supplied with steam direct from the boiler. The argument in favour of this arrangement is that side-jacketing of the low-pressure cylinder involves a large absolute waste of heat that goes towards heating the exhaust steam as it leaves the cylinder on its way to the condenser; this loss of heat by the jacket steam being noxious, not only because it is pure waste, but also because it raises the back pressure against the piston. The fresh steam in the hollow piston sweeps over the inside surface of the cylinder just in front of the incoming working

steam, and thus heats the metal and prevents undue condensation of the working steam, while it is comparatively inactive in heating the back-pressure steam. In criticism of this argument, it may be remarked that towards the end of the stroke (during the last quarter of the stroke) this piston-jacket surface giving heat to the exhaust-steam is greater than a side-jacket would offer. For three-quarters of the stroke, however, it is less.

Each cylinder is connected with the fly-wheel shaft by a cross-beam. Over each end of each beam stands a single-acting, air-compressing cylinder of 26 inches diameter and 48-inch stroke. Each engine thus drives six of these air-pumps; and, since the speed is ninety double strokes per minute, the volumetric capacity of the compressors of each engine is close on 8000 cubic feet per minute.

The pressure in the mains is to be 45 pounds per square inch above the atmosphere, and the delivery-valves are expected to lift a little before three-quarters of the compressor piston-stroke is finished. Thus the volume of air compressed to the above pressure delivered per minute by each engine is taken as about 2000 cubic feet.

147

=

The ratio of pressures is 597 = 406. Thus, if the compression curve were isothermal, the valves would lift, as above assumed, at 75 of the stroke. If it were adiabatic, this pressure ratio would correspond to a ratio of final to initial volume of 367, and the valves would lift at 63 of the stroke. If the curve lay exactly mid-way between these two, or were according to the law, the ratio of final to initial volume would be 31, and the valves would lift at 69 of the stroke. In the latter case the volume delivered would be 31 x 8000 2480 cubic feet per minute. Calculating simply from the product of this volume by 45 pounds per square inch pressure (i.e. from the work the air could do in an air-engine without clearance, without expansion, and without more than atmospheric back pressure), this would give about 487 horsepower delivered in the consumer's engines for each engine developing 1000 horse power at the central station. Two indicator-cards taken from two air-compressing cylinders at Frood Colliery, near Wrexham, give very different results, possibly because one compressor was near the steam-engine cylinder, and was heated by it, while the other was not. The compression-curve from the one cylinder corresponds with the relation pv, while that from the other corresponds to px. The latter curve is thus much steeper even than the adiabatic, and would indicate that the air was actually heated by conduc tion or radiation during its compression. Such heating could hardly have taken place to such an extent as to account for the above very high index, and the more probable explanation is that the air was steam-laden as it was taken in, and that the extra rise of pressure is really due to that of the steam in the mixture consequent on the rise of the temperature.

It is desirable to keep down the compression-curve as nearly as possible to the isothermal line, because by doing so the area of the compressor indicator-card, and therefore the work to be done by the engines, is kept down to its minimum; whereas no advantage can be derived from the increase of temperature obtained by adiabatic com pression, because this is rapidly lost by cooling in the pipes long before the air is utilised in the air-engine it drives. It is worth noticing that, because of the air being discharged from the compressors through valves which automatically lift when a certain designed pressure is reached, this loss of power due to cooling in the pipes is effected rather by a contraction of volume than by a diminution of pressure. The decreasing-pressure gradient along the pipes is very small, and is due solely to frictional and viscous resistance to the flow, and to variation of velocity consequent on variation of section.

In order to approximate to isothermal compression,

that the steam is supplied to the piston-jacket of the lowpressure engine cylinder; but this refinement has not been deemed necessary in the design as at present adopted.

The compressor piston-face travels a little beyond the position assumed by the flat face of this delivery-valve when the latter is closed. During the momentary pause at the end of the stroke, the valve therefore falls into actual contact with the piston-face, and the two descend together until the valve is landed on its seat. Thus the clearance space is reduced absolutely to zero. The suction-valves are somewhat similarly arranged so as to reduce the clearance at the other end of the stroke to a very small amount. The cooling-water is circulated by gravity from a tank giving a head of 20 feet. The water is pumped into this tank from the canal, and the power spent in pumping this water is a partial set-off

against the economy resulting from the approximation to isothermal compression; but the power thus gained greatly outweighs the work spent in this pumping.

As at present designed, the air-pipes are of wroughtiron plate, riveted, but a new design for plate-steel tubes is being considered. The pipes are to be laid in concrete tunnels, which free them from all pressure of superincumbent soil or paving, and will always be very accessible for examination and repair. They are of 24 inches diameter near the central station, and diminish to 7 inches in the smallest branches. The joints are given a small degree of flexibility. In one design they are formed by two angleirons riveted to the outside ends of the two pipes, a hard rubber ring of circular section being placed between the flanges thus formed, and the flanges being drawn together by bolts. In another design a sort of double-socket coupling-piece covers the ends of both pipes for a few inches; the end of each pipe has formed on it two slightly

projecting rings, and between these is poured, in the molten state, through a hole in the socket-coupling, a soft metal that expands during solidification. We rather doubt whether this last design will give sufficient tensive strength to the joint. Tensive strength is required simply because there are necessarily bends in the pipe here and there.

The air is supplied to the consumer through a registering meter. This meter is similar in construction to Beale's gas exhauster. It consists of two cylinders, one inside the other. Both are 4 inches long; the outer one has a diameter of 14 and the inner a diameter of 9 inches. The outer one is fixed, and is furnished with an inlet and an outlet opening. The inner cylinder revolves freely on a fixed axis, distant (14-93)= 2 inches away from the centre of the outer case, so that the two cylinders always touch along a fixed line. Two sliding shutters project from a slot through the centre of the revolvi

cylinder. By means of a pin and a pair of sliding blocks running in circular grooves cut on the inner surface of, and concentric with, the fixed cylinder, these shutters are drawn out and in from the revolving cylinder so as always to keep in contact with the fixed one. During one revolution these shutters sweep through the meter a volume of air about 17 cubic feet.

This rotation is reduced three times by worm-gearing in being transmitted to the counter-box, so that a single dial with two concentric circular scales, which are read by two fingers like the hour- and minute-hands of a common clock, is sufficient to register up to a million cubic feet. Fig. 1 shows this meter. It is driven by a small difference of air-pressure between the inlet and outlet. The Company intend to charge at the rate of 5d. per 1000 cubic feet at standard pressure of 45 pounds per square inch. If the air were used in an engine without expansion, without clearance space, and without back pressure above the atmosphere, this would correspond to a cost per hour per indicated horse-power of

pure rolling action at one or other side of its tread. The wearing might not be of much consequence in itself, ex cept that it gradually vitiates the accuracy of the indica tion; and besides, the velocity ratio is uncertain because of the contact taking place over a perceptible range of radius. There ought to be an idle roller between the disks opposite the driving roller, and both disks ought to be pressed inwards by springs, instead of one only. But the chief defect is in the principle of the construction, which does not make the dial-indication proportional to PV as it ought to do. If R, be the disk radius at which the roller would stand when zero pressure existed in the Bourdon tube, and if Cbe the inward movement per pound per square inch rise of pressure, and if r be the radius of the roller, then at pressure P the contact radius on the disk will be Ro- CP, and the fractional revolution of the disk per revolution of the roller is This is not proIts differential coportional to P as it ought to be. efficient with respect to P should be constant, whereas it Cr is really The converse gearing ought to (R-CP) be substituted; that is, the volume-meter should be geared positively with the disk, and the disk should drive

r

R-CP'

indicated horse-power will cost per hour from 2d. down to as low as 1d., excluding cost of engine attendance and depreciation, and interest on first cost of engine.

FIG. 3.

contact.

The rotation is transmitted to a small roller on a spindle capable of sliding in its bearings parallelly to its own axis. It drives a disk on the counter-arbour by rolling The end of the roller-spindle is linked to the end of the tube of a Bourdon pressure-gauge. As the pressure rises, the roller is thus pushed nearer the centre of the disk, and gives this disk, therefore, an increasing fraction of a revolution per revolution of the roller. The roller really lies between two disks, but the one is "idle" and serves simply to support the roller in pressing against

the driven disk.

This integrator is wholly wrong in principle, and it is badly designed in detail. The roller has a rubber tyre round it, and therefore touches the disk at different radii,

and thus must rapidly wear away, owing to the want of

The registrations of all the meters in the whole district are telegraphed to the central station and added up on one large central counter, so that the engineers in charge consumption with the duty of the engines, known from may have means of continually comparing the actual ordinary engine continuous counters, and of detecting any serious leakage that might occur in consequence of breakage of a main or branch pipe. The telegraphing apparatus is shown in Fig. 3. The counting disk is divided into ten equal divisions, each representing 1000 cubic feet, by small metal projections. As these come successively underneath a contact-maker, they allow the passage of a through a corresponding division. One main wire, with current, which moves the finger of the central counter branches to the separate meters, is sufficient for the whole district, the earth return being used. As the counter-disk moves slowly, special means must be taken to break the

called "efficiencies" it is difficult to understand. The consumer is supposed to supply a large extra amount of power at his own cost by burning gas to heat the air, and it seems an extremely evident misuse of the word "efficiency" to apply it to the ratio of the diagram so got to the diagram of the central station engine. By a little more liberal burning of gas, the efficiency obtained by this method could quite easily be made higher than unity. On the same principle we might calculate the efficiency of a steam-engine by taking the ratio of the indicatorcard from the steam cylinder to that taken from the feedpump that supplies water to the boiler, and thus obtain an efficiency of, let us say, 50,000 per cent. This is a reductio ad absurdum of the method of calculation which is perfectly legitimate and logical. R. H. S.

THE CLASSIFICATION OF THE CÆCILIANS Na paper on the structure and affinities of the Amphiumidæ, published in the newly-issued part of the Proceedings of the American Philosophical Society (vol. xxiii. No. 123), Prof. Cope has put forward some views as to the position of the Cæcilians or Apodous Batrachians in the Systema Naturæ, which are worthy of careful consideration. The Cæcilians, Prof. Cope observes, are generally regarded as representing a distinct order of the Batrachian class, which bears the name "Apoda," or "Gymnophiona." The definition of this order given by Mr. Boulenger in his recently published Catalogue of the specimens of these animals in the British Museum is: "No limbs; tail rudimentary; males with an intromittent copulatory organ; adapted for burrowing." Of these definitions Prof. Cope maintains that not one is of ordinal value. "The tail in some Cæcilians is distinct. The intromittent copulatory organ in such species as Dermophis mexicanus, Gymnophis proximus, and Herpete ochrocephala is not a special organ, but merely the everted cloaca. The hard papillæ observed by Gunther in Ichthyophis glutinosus are wanting in the above-mentioned species, and the protrusion of the cloaca is performed by two special muscles."

As regards the absence of limbs in the Cæcilians, Prof. Cope points out that the extremely rudimentary character of these organs in Amphiuma is well known, and that their non-existence has no greater claim to be considered as of ordinal value in the Batrachians than in the adjoining class of Reptiles, where it is in some cases not even a "family" character. Looking to these facts, Prof. Cope proposes to unite the Cæcilians with the Urodele Batrachians, and to class them only as a family, "Cæciliida," connected with the more typical forms of the group through the Amphiumidæ.

Messrs. Sarasin, who have recently published a most interesting account of their observations on the development of a species of Cæcilian in Ceylon,' seem to have come to nearly the same conclusions as to the correct systematic position of this group of Batrachians.

NOTES

THE Prince of Wales has requested the President of the Royal Society to join the Committee appointed to advise on the organisation of the proposed Imperial Institute.

WE have referred elsewhere to some of the possible results of the meetings held last week in favour of the Imperial Institute. Some very striking features which have been developed in connection with this movement during the last week are, first of all, the considerable desire which has been evinced, to enrich various localities with some Jubilee memorial, and, again, the wisdom "Ueber die Entwicklungsgeschichte von Epicrium glutinosum,” Arb. Zool. Inst. Würzburg, vii. p. 202 (1885).

generally displayed in selecting worthy local objects, such as museums, improved science schools, and the like. All this of course is admirable and entirely to be applauded, but believing as we do that there is a possibility of the Imperial Institute, if properly conducted, doing more good for the future development of science and commerce in Greater Britain than any other single organisation can possibly effect, we hope that it will not be starved in favour of merely local objects. We hear that the women of England have already subscribed a noble sum. This no doubt Her Majesty will hand over to the Institute, if it is organised so as to command the confidence and respect of the various leaders of opinion in this country and in the colonies.

MANY of our readers will attach much importance to Colonel Donnelly's letter, which appears in another column. A large increase in the number of students anxious to enter the Normal School of Science and Royal School of Mines was of course to be expected, and we are glad that this influx has induced the department to take steps to increase the accommodation, and at the same time to insist upon one of the best possible forms of entrance examination; a strict inquiry, namely, into the educational history of each candidate for admission.

THE Norwegian Government has presented a Bill to the Storthing for fixing a standard time for the whole of Norway, The standard time proposed is Greenwich time plus one hour.

MR. W. BALDWIN SPENCER, Fellow of Lincoln College, Oxford, has been appointed to the Chair of Biology in the University of Melbourne, and will leave England in about three weeks. Mr. Spencer distinguished himself lately by his important memoir on the pineal eye in lizards.

A NUMBER of eminent men of science have addressed a

memorial to the President, Vice-Presidents, and Council of the Royal College of Surgeons of England, suggesting that the legacy bequeathed to the College by the late Sir Erasmus Wilson might with advantage be devoted to the establishment of an institution having for its object "physiological and pathological research." It is pointed out that the want of such an institution in England has long been felt, and more especially of late, when we have had to look to Berlin for information respect ing tubercle, and to Paris for experiments on the prevention of hydrophobia. That the Government will do anything in the matter no one is so sanguine as to believe; and it is hardly more probable that the want will ever be supplied by public subscription. There is, therefore, much to be said for the present proposal, and the authorities of the College of Surgeons will, no doubt, give it due attention. It seems strange that in London there should be nothing like the splendid laboratories which exist not only in the capital cities of Europe, but in comparatively small German towns, such as Bonn, Strasburg, and Leipzig.

UNIVERSITY COLLEGE, Liverpool, has reason to congratulate itself on having some remarkably generous and enlightened friends. On Tuesday last it was announced at a meeting of the College Council that Mr. Thomas Harrison, shipowner, of Liverpool, had endowed the Chair of Engineering with 10,000/ Only a few weeks ago Sir Andrew Walker, also a citizen of Liverpool, gave 15,000l. to build Engineering Laboratories.

ON Thursday last the honorary freedom of the City of London was conferred upon Mr. H. M. Stanley, in recognition of his services as a traveller and explorer in Africa. The presentation was made at a special meeting of the Court of Common Council in the new council chamber at the Guildhall. The City Cham berlain, in making the presentation, referred to "the remark able development of journalistic enterprise during the Victorian era," observing that Mr. Stanley was the first member of "the