the following experiment: First, turn off the air supply and a flame does not light the unbroken oil jet. Next, allow the air under pressure to break up and thoroughly spray the oil, the vapour formed is so intimately mixed with air that it can easily be ignited, and burns with a bright flame. The drawings of this spray-maker also show the governing arrangement adopted in the Priestman engine. The amount of hydrocarbon is diminished or increased, together with the amount of air, so as to form a high explosive charge or a low one, according to the amount of work to be done by the engine. The air through the wing valve is rightly proportioned to mix with the oil which is allowed through the V-shaped slot cut in the conical plug regulated by the governor. By this means there is a regular explosion and impulse, every cycle giving admirable regularity of running. The compressed charge is fired by an intermittent electric spark, made to play between ends of two platinum wires insulated by porcelain in the igniting plug (shown), and connected to an induction coil excited by a storage cell of about two volts, which has been known to work for more than 1,100 hours. Each cylinder of launch engine is 7in. diameter by 7in. stroke, arranged to give an explosion or working stroke every revolution of flywheel. The actual horse-power at 250 revolutions per minute is 57, and 9.1 i.h.p. These engines are working in a small launch 28ft. from stem to stern by 6ft. 2in. beam, and are giving good results. Speed seven miles, and engines work with regularity. These engines are now in use on barges in canals, and also for deep-sea trawling. The horizontal type is remarkably self-contained, and well adapted for isolated electric lighting installations and lighthouse work. It is used for pumping and hauling in collieries, and for rock-drilling in mines; in fact, its sphere of usefulness is rapidly extending, because it is found reliable and steady at work, with decided economy of fuel. This is secured by thoroughly mixing the air and vapour, so as always to form an explosive mixture which gives complete complete combustion and clean exhaust. It must be pointed out, however, that during the compression of the charge before ignition a considerable proportion of the vapour comes into contact with the walls of the cylinder, condenses on them, and never gets burned, however useful it may be for lubrication. This I have proved by comparing the pressure along the compression curves of the indicator diagrams, with the pressure obtained by experiment from each charge consisting of the explosive mixture, 015 cubic inch of oil and 191 cubic inches of air at the same temperature. Taking the temperature of the charge, 170deg. F., on entering the cylinder, the indicator diagram shows the highest pressure before ignition only 381b. per square inch. This is kept low for fear of much condensation, as well as to give smooth running. In the gas engine we know that compression of the charge before ignition is essential to high efficiency, and similar considerations lead one to expect the same to hold true for oil engines. Indeed, by adding fresh air to the charge after leaving the vaporiser, and compressing more than usual, greater power or higher efficiency is obtained, but the temperature of the cylinder becomes too high for lubrication. In some published trials an engine may be run with a special cylinder liner to withstand the high temperatures due to high compression used, but these are not the conditions for ordinary work. In fact, for any particular oil experience must decide the degree of compression that gives best results as regards power and efficiency consistent with economy and durability of engine. I may here briefly notice my investigation of the relation between the pressure and temperature of the vapours from different burning oil, intermediate oils, and some heavier lubricating oils, in order to throw some light on the action in the cylinder of the common oil engine. At the same time I have tried to find out which oils are best adapted for this My experiments prove that notwithstanding the complex and varied character of the different oils examined, the law according to which the pressure of petroleum vapour varies with its temperature is represented by a perfectly regular curve for each oil. Compare these results with the figures obtained from the different oils when used in the same engine during special tests for the purpose.

use.

By far the simplest type of oil engine is that in which the oil is injected directly into compressed and heated air

in a cartridge, which at once acts as vaporiser and combustion chamber. Such an oil engine is the invention of Mr. H. Akroyd Stuart, of Bletchley, and is now being made by Messrs. Hornsby and Sons, Grantham. A novel feature of this engine is that the ordinary gear for firing the charge by heated tube, flame, or electric spark, is dispensed with altogether, and heavy intermediate oil is ignited and completely burned when injected into the compressed and heated air in the red-hot vaporiser or cartridge. This chamber is heated up at start with a special oil lamp supplied with air-blast by a small fan, as shown in drawings. One sees by the wall diagrams that this engine is of the simplest design. The working parts are few and simple, and some details are being improved by Messrs. Hornsby and Sons. The oil-cistern is fitted in the base of the casting, exposed to ordinary atmospheric pressure, and the oil supply can easily be replenished at any time during a run by sliding open a top cover and pouring in the oil. Every charge of oil is forced, by means of a positive action oil pump, through a thin pipe and simple nozzle into the vaporiser at the proper moment for ignition, just after the hot air has been compressed and the piston is on the return stroke. The oil supply is regulated by a governor, whilst by using a large flywheel and high speed, about 210 reospermins, this engine runs very steadily. I tried a 6-h.p. engine during a run of about three hours, using oil of specific gravity 854, and flashing point 220deg. F., and the consumption was less than a pint per brake horse-power per hour. Even heavier oils might be tried, the hot water from the water-jacket going to warm up the heavy oil and keep it in a fluid state fit for use in winter.

The action in the engine cylinder is here very different from that in the Priestman, inasmuch as there is an excess of air in the cylinder, and this is compressed before the oil is injected. Consequently, the combustion is rapid and will be complete even when heavy oils of great heating power are used. However, since the air is dry, and there is no condensation of oil, the cylinder requires independent lubrication, as in the case of the gas engine.

A feeling of safety to the public naturally tends to the use of heavy oil, from which the lighter constituents have been distilled. I have found the loss in weight of some heavy oils by prolonged heating at low temperatures, keeping the oils exposed to the air and allowing free evaporation. Known weights of oil were taken in shallow dishes, about 3in. across top, and gently heated on a sand bath by a very small steady flame for three hours, the temperature of the oil being kept constant. The proportion of volatile constituents present in the samples are indicated.

EVAPORATION.

The terribly explosive character of the hydrocarbons driven off at the ordinary temperature renders the safe storage of petroleum imperative. Instead of the present tank system, Mr. B. H. Thwaite has devised the safety oiltank which the wall diagram and model explain. It is very much like a gas-tank, the cover-plate being kept in contact with the oil and counterbalanced by weights to give only a slight pressure of lin. or 2in. of water on the surface of the

oil. The frame moves into an annular water seal standpipe, to draw off any gas that collects. There is no necessity for the introduction of air to allow the tank to be emptied, and as the oil is kept cool, and always under pressure, it is impossible for a dangerous explosive mixture

to accumulate inside the tank.

not, perhaps, an excessive amount-we have £400 gone, probably a large fraction of the amount needed to erect the whole installation. Nineteen of those Nineteen of those tendering would lose the contract, and one would gain it; the cost of the nineteen will have to be borne by someone-not the Local Board of Festiniog. If the Local Board wish to obtain a benefit from their water power they ought to be, and we hope they are, prepared to spend sufficient at least to save contractors the expense of preparing for them definite proposals, besides that of giving all required information as to prices in public tender.

LITERATURE.

New

The Arithmetic of Electrical Measurements, with Numerous Examples Fully Worked. By W. R. P. HOBBS. Edition. Murby, 3, Ludgate-circus-buildings, E.C. This book, as the title indicates, is merely a collection of questions requiring numerical answers involving the simpler formulæ connected with electrical work. We quite agree with the author that mere reading will never make an electrician, just as the mere reading of a book on building would not much assist the navvy in tying a putlog to a scaffold pole. Many people who fancy their knowledge of a subject to be exact and extensive would have a bad quarter of an hour answering the questions of an audience after giving a popular lecture on the subject. Two of the best ways of learning the kind of knowledge you possess will be to undertake to deliver a popular lecture upon an engineering subject before a body of working engineers, or to give written answers to a series of simple questions. Difficult problems will take care of themselves. Men of leisure and brains will always be found willing and ready to undertake the investigation of the unknowable and erect hypotheses thereon. What we want is books of this simple character and an extensive use of them.

Telegraphy. By W. H. PREECE, F. R.S., and J. SIVEWRIGHT, M.A., C.M.G. Ninth Edition. Revised and Enlarged. Longmans, Paternoster-row.

A book that has gone through nine editions needs little to be said as to its merits or demerits. Proof has been emphatically given that the former are prominent and the latter hidden. Such might not be the case perhaps if there were no other books on telegraphy, but, as is well known, their name is legion; hence the greater the pronounced success of this book. Yet there ought to be no difficulty in understanding this success. The authors have been in the forefront of telegraphic work during the whole of their working lives, have had exceptional facilities for becoming acquainted with every new detail in the progress of the last quarter of a century, and, what is of far greater importance, are in the position of knowing exactly what improvements have proved successful in practice, and what designs have failed when put to the test. Some years ago now, and in a publication not directly connected with the electrical industry, we remember mildly suggesting inability-an inability still holding to quite agree with the way in which the term "quantity" is used in the second paragraph of this book. Other than this, we have nothing but praise for the matter and method of the book.

CARBON SWITCH,

The Allgemeine Company, of Berlin, have recently introduced a carbon switch, Fig. 1, for the gradual breaking of the field-magnet circuits of large dynamo machines. With ordinary quick-break switches the breakage of a large current, owing to the self-induction, often generates a very high momentary pressure, which may easily pierce the

These engines are specially adapted for driving overhead shafting, to which the engine crankshaft may be coupled direct, the engine being placed on the outer side of the end

wall of the building, and protected by a small shed with lean-to roof. By this arrangement the engine is readily accessible, and, while it is protected from the weather, the working parts are preserved from injury by the dust and dirt of the workshop, an important consideration in connection with certain industries.

The engine being fixed to the end wall of the building, the crankshaft occupies a position at right angles to the face of the wall, and any stress due to the vibration of the engine is transmitted to the wall in a direction parallel with its length-i.e., in the direction in which the wall is best suited to withstand such stress. These engines, therefore, obtain a distinct advantage over the usual form of wall engine, which is bolted to one of the side walls of the building, in which latter type the crankshaft being parallel with the face of the wall, the stress is transmitted to the wall in the direction at right angles to its length. Where the speed of the shop shafting does not correspond to the speed of the engine, the latter may conveniently be arranged to drive the shafting by belt.

The engine frame, with the guide-bars, is in a piece with one of the plummer blocks, and is bolted to a casting which forms the outer plummer block, and which in some cases is brought up so as to form a box above the crankshaft, thus supporting the wall over the engine. The centre casting, at its further extremity, is rigidly secured to a large wallplate arranged on the opposite side of the wall to the engine cylinder; the bolts securing the engine to the wall passing through this plate, any possibility of either plummer block springing is thus avoided.

These engines are sometimes made with a double crank, so that the power can be taken off from both ends of the crankshaft. Each engine is fitted with a sensitive governor acting direct upon an equilibrium piston valve, and efficient means of lubrication are provided.

SUNBEAM LAMPS.

Mr. J. W. Swan once publicly expressed his opinion, if we rightly remember, that the arc lamp had but a very limited application, and that eventually incandescent lamps would carry nearly everything before them, both for public and private lighting. Now, although there is much to be said pointing to the great extension of arc lighting throughout the world, it certainly seems, more particularly in this country, that the arc light is very far indeed behind the incandescent lamp as a lighting agent. Everywhere we are beginning to see incandescent lamps burning-in houses, shops, and factories-and but seldom the arcs. Incandescent lamps are made by the million, arcs by the dozen or the hundred.

The reason of this is not far to seek. In spite of the lesser current for the greater light that the arc lamp gives, daily attention is required, daily consumption of carbons is experienced, while the incandescent globe burns right through, with but occasional need for attention beyond the turning of the switch. It is for this same reason that the high power incandescent lamps-better known under the name of "Sunbeam" lamps have found so much favour for large candle-powers. With them, also, no daily attention or renewal is required, and, in addition, we have a perfectly steady and withal a warm light, which, especially for large halls, seems to be infinitely preferred to the intense glare and dazzling intensity of the arc lamp. There is no bissing or blinking, and they require no attention from the time of their first instalment till they give way-a matter of months, many or less, according to use. With reference to ordinary inside lighting these lamps also have their considerable use; for when dealing with large shops, halls, or stations and so forth, it is often very greatly preferable to use one large incandescent lamp than many small ones, both as regards the first cost of wiring and lamps, and also the cost of renewals.

These high-power Sunbeam lamps are made usually in two classes: one of long-duration carbons, for places where current is cheap and lamps are a consideration-for a factory producing its own electricity, for instance; and the other of high-efficiency carbons, for situations where current is the chief consideration. We give below the

These lamps are made for running in series for a current of 5, 6, 8, or 10 amperes, on their own or on an arc lamp circuit; these series lamps are made of various candle-powers.

As the efficiency of these high-power lamps is very high, special care should be taken when using them that the voltage of the current never exceeds that for which the lamps are required. Want of care in this respect, or the use of a pulsating or irregular current, is found to be the most frequent cause of failure of incandescent lamps.

FRANKFORT EXHIBITION.

Messrs. Felten and Guilleaume, the well-known firm at Mülheim-on-Rhine, exhibit largely in the so-called Distribution Hall, where all conducting material and systems of distribution are shown. A part of their show is seen at once on entering through the northern entrance, and the remainder is immediately adjacent on the left. The former contains more particularly the cables and insulated wires, as well as two fully-mounted nets of cables for electric lighting-i.e., one each on the three-wire system and for alternate current. In the side room a Ferranti cable is shown in the different stages of manufacture, with joints; also uninsulated wires of different materials and for various purposes, and wire ropes are exhibited.

The principal exhibit of Messrs. Felten and Guilleaume's is, in common with Schuckert's, surrounded by six high candelabra with Schuckert's arc lamps, and four smaller ones with Schuckert's glow lamps. Short pieces of wire rope made of fine wire form in combination with the candelabra and some columns a balustrade, which closes the show against the passengers. The two large pictures suspended between the small candelabra show the two works of Messrs. Felten and Guilleaume-namely, the Wire, Wire Rope, and Cable Works, Carlswerk, at Mülheim-on-Rhine, and the Hemp Spinning Mill and Mechanical Twine Factory, Rosenthal, at Cologne. Above the passage to Schuckert's show a 27-core aerial telephone cable is suspended to a wire strand fixed to the candelabra. Aerial wires are stretched higher up on the two sides, these aerial wires being connected to the telephone cable by means of joint-boxes and intermediate rubber cable.

In the corners next to the entrance there are on the left a column built of galvanised wire and wire strand, on the right a similar column formed of copper and brass wire, lead coated copper wire for accumulators, and copper strand. The two columns on the right and left of the passage to Schuckert's show represent the different kinds of cables, as lead-covered cables, cables sheathed with wire, and iron tape rubber cables, house leads, etc.

The attention of the visitor on entering from the north