Gas at a low price, much lower than that at which it is now generally sold by gas companies, is one of the desiderata to which gas engine builders and users alike have been looking forward for some time. It is not that the gas engine, even with the current prices of gas, is by any means unduly expensive in point of fuel, but it is manifest that with cheaper gas the full possibilities of motors of this type would be more readily and widely appreciated, and could be more strikingly emphasized by the probably greatly increased numbers in use. In one of the preceding papers a few figures were given, showing what was actually accomplished with a cheap heating gas in the line of reducing the cost of power in a gas engine. Unfortunately, however, enterprises of the character there mentioned, keeping in view the manufacture and distribution for general consumption of low cost gas for heating purposes, have not yet been pushed to any extent, and users of the larger sizes of gas engines, developing about forty horse-power and more, who have been impressed with, and who decided to profit by, the economies of cheap gas utilization have been obliged to avail themselves of special gas producer outf1ts to be worked in conjunction with their engines, just as steam boilers ordinarily are operated in connection with steam engines.
This plan of putting in independent gas producers has been specially developed in England, and a comparatively large number of such gas plants on the Dowson system have been built and operated with the most satisfactory results. The outfits, as generally used, consist of a small gas holder and tank with a scrubber placed inside the tank. The scrubber is filled with coke or other suitable material, and the gas, as made, is passed through this before it reaches the holder. A regulator on the gas producer governs the production of gas, within certain limits, by the rise or fall of the holder, and makes large storage capacity unnecessary. In some of the outfits an escape valve has been used on top of the holder to let off gas into the open air or up through a waste pipe when the holder is full, and when the make of gas exceeds the consumption. This, however, has not been employed to any great extent, since the regulator arrangement satisfactorily provides for fluctuations in consumption and avoids the waste of fuel.
The gas is made by forcing a continuous current of steam and air through a coal fire in the producer proper, or generator, so that the necessary high temperature of the fire is maintained while a constant volume of steam is decomposed. The oxygen of the air and steam combines with the carbon, producing carbonic oxide which is rendered still more inflammable by the hydrogen set free by the steam. The total cost of the gas, including wages, etc., and allowing for the increased volume of the gas required to develop the same power as coal gas, has been found, it is stated, to be equal to coal gas at about forty cents per 1ooo cubic feet. The result of this certainly very acceptable price has been, as already intimated, the installation abroad of quite a large number of Dowson producers for private use, and the gradual adoption of gas engines of larger and larger sizes, so that now there remains very little cause for the impression, still entertained by some, that the gas engine is essentially a small power motor. In the United States, combination engine and producer plants are not so well known, or, at least, not so much used, but their advantages are pretty well appreciated, and their more extensive introduction would seem to be a matter of but a few years. Plants of this kind are already in use there in several places, and, from all accounts, seem to be doing satisfactory work. Where they are put in, one is, of course, entirely independent of gas companies, just as in the case of oil engines, the whole outfit being complete in itself.
Careful tests of Otto engines working in conjunction with Dowson producers, as already stated in one of the preceding papers, have shown a fuel consumption as low as 1.2 pounds of coal per indicated horse-power per hour, and Messrs.
Crossley Brothers, of Manchester, the English builders of the Otto engine, in the early days of Dowson gas found that the wages of a fireman for several gas generators are not more than those for a set of steam boilers. The gas also can be conveyed with little loss from condensation to various parts of a large establishment using power, and independent gas engines can thus be employed for different lines of shafting. Any department working overtime can have its engine supplied with gas from a single generator, and all the advantages can in this way be secured that are usually claimed for, and achieved by, the system of sub-division of power.
/fig. 45.jpg) Fig. 45— The Safety Vapor Vertical Gas Engine |
To return, however, from this brief digression to the descriptions of currently used engines, we will present, to begin with, the so-called "Safety Vapor" engine, shown in Fig. 45, and put on the market by the
Safety Vapor Engine Company, of New York. A feature at once noticeable in this engine, which also works on the Otto cycle, is the chain or link belt shown at the right, operating the valve. The latter is simply a flat, circular plate with one port cut through it in the shape, nearly, of a sector of a circle. The valve seat is provided with two similarly shaped ports placed close together, one for admission of the charge into the cylinder, and the other for exhaust.
Two ports, exactly the same in shape and similarly located, are provided in the cover plate which holds the valve in position. One of these ports communicates with the exhaust pipe and the other with the gas and air supply pipe. The valve, it will be understood, rotates constantly in one direction and as the port in the valve establishes communication between the first seat port and the corresponding port in the cover plate, exhaust takes place. The valve, proceeding further around, next brings its port over the adjoining admission ports in the seat and cover plate, and the charge of gas and air then enters the cylinder, and is subsequently compressed, ignited, and expanded while the valve completes its revolution until its port again establishes communication between the exhaust ports. This completes one cycle. The. valve, of course, makes only one revolution for every two revolutions of the crank-shaft, the large link belt pulley above having twice the diameter of the smaller pulley below which drives it.
The gas goes to the engine through the horizontal branch pipe, shown at the left in the illustration, passes through a graduating gas valve by which the gas supply, and consequently the speed of the engine, can be regulated, and then mixes in a pipe chamber with air taken in through the vertical pipe shown extending downward. The mixture finally enters the admission compartment of the valve chest. Ignition of the charge is effected electrically by a spark passing between two electrodes in the extreme upper end of the cylinder, the current being furnished by an electric battery. Special electric contact strips are arranged on the valve chest cover and are brought together once in every revolution of the large link belt pulley operating the valve. By this arrangement a spark between the electrodes in the cylinder is produced once in every two revolutions of the crankshaft, or at the beginning of every fourth stroke of the piston.
The engine, as shown in the illustration, is arranged for use in a launch and for this purpose is f1tted up with a friction driving gear for the propeller shaft. This gear is similar to the one already described in connection with the Kane electro-vapor launch engine in the April number, and its action will be at once understood from the illustration. There are, as will be observed, two friction wheels, mounted in a frame pivoted on the propeller shaft. The latter carries a third and larger friction wheel, which is in contact with the other two. By means of a lever extending upward, the frame with its two friction wheels, may be thrown over to either one side or the other, bringing the wheels into contact with the rim of either one of the engine fly-wheels and thus causing the propeller shaft to revolve in either direction as desired, driving the launch either ahead or astern. When the friction gear lever is in mid-position, both of the small friction wheels are out of gear, and the engine revolves idly, the propeller shaft being at rest. The stationary engine is exactly similar to the marine engine, except that it is provided with a governor belted to the engine shaft and controlling the main gas valve, either reducing the amount of gas admitted or cutting off the supply altogether when the speed of the engine rises above the normal. The engine is built in sizes of from one-half to six horse-power and, as may have been already gathered from the fact that it can be applied to boat propulsion, is adapted to the use of gasoline as well as gas.
/fig. 46.jpg) Fig. 46— The Rollason Horizontal Gas Engine |
| /fig. 47.jpg) Fig. 47— The Rollason Vertical Gas Engine |
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The Rollason gas engine, of which both horizontal and vertical designs are shown in Figs. 46 and 47, is the invention of Arthur Rollason, and has been used in England for several years with very satisfactory results, the English builders being Messrs.
Wells Brothers, of Sandiacre, near Nottingham. It is now also being made in the United States by the
Electric Manufacturing and Gas Engine Company, of Greenbush, N. Y.
When first brought out, the engine was of the three-cycle type, that is to say, there was in ordinary working, one explosion or impulse in every three revolutions or in every six strokes. An explosion having taken place, the piston made a forward stroke under its impulse; then the exhaust valve was opened, and the piston on its return expelled a large proportion of the products of combustion. During the second forward stroke the piston drew in behind it what was termed a scavenger charge of air which it forced out on the back stroke together with what remained of the burnt gases. On the third outward stroke a combustible charge of gas and air was drawn in, and on the next back stroke, or sixth stroke, this mixture was compressed ready for ignition. This completed the cycle, and the engine was then ready to again go through the same series of operations. In the engine as now built, however, a four-stroke cycle is followed,
and yet the use of the scavenger charge is retained, a feature which is probably not found in any other four-stroke cycle gas or oil engine now on the market. The particular advantage of a scavenger charge of air will be appreciated when it is borne in mind that ordinarily the clearance spaces in a gas engine cylinder are filled with used-up gases when the fresh charge of explosive mixture enters the cylinder, and these remaining burnt gases probably exert a delaying action on the explosion.
/fig. 48-49.jpg) Figs. 48-49— Sectional Views of the Rollason Engine |
The interior construction of a portion of the Rollason engine is shown in the sectional views Figs. 48 and 49, from which it will be seen that in front of the cylinder is a long tubular guide in which works a second piston rigidly connected to the front. This tubular guide and piston constitute a pump in which air, slightly compressed, forms the scavenger charge. Air enters through the valve F in the bed-plate, and gains access to the passage E, one end of which communicates with the pump and the other end with the air valve entering the main cylinder. On the suction stroke of the main piston, air is drawn into the pump, and a gas and air mixture into the cylinder. On the compression stroke the air is compressed in the pump, but only slightly, because the clearance space is so large. On the explosion stroke this air is expanded. As soon as this stroke is completed, the exhaust valve C opens, and the main piston, returning, sweeps the products of combustion before it, while the pump piston compresses the air. Shortly before the end of this stroke the air valve is opened and allows the compressed charge from the pump to rush into the cylinder and out through the still open exhaust valve. The exhaust valve is kept open until the crank passes the centre, affording ample time for all the products of combustion to be completely swept out. The annular gas valve is then opened and the motor piston draws in its charge.
The regulation of speed in the large engines is effected in two different ways. There is a centrifugal governor connected with a throttle valve, and small variations of load are met by reducing the strength of the charge. If the speed is greatly increased, however, the gas valve is not opened at all. It is worked by a hit-and-miss device, and at high speeds a cam connected to the governor trips the device and cuts off the gas.
The admission and exhaust valves are of the poppet type, and the original slide-valve design has been abandoned as in most other makes of gas engine. Firing of the charge is effected by a tube igniter.
/fig. 50.jpg) Fig. 50— Valve Gear Detail of Rollason Engine |
The nature of the valve gear will be made clear by an examination of Fig. 50, which represents a cross-section of the cylinder and of the valve chambers. The explosion or combustion chamber,
A is surrounded with the usual water jacket and has the passage a through which air enters on its way to the air admission ports b. The lay-shaft,
B is driven from the crank shaft by reducing gearing and is provided with a cam,
C, for operating the igniting device, and with a second cam,
D, for governing the admission valve
E and exhaust valve
F through the intervention of a two-armed rocking lever pivoted at
G. This lever carries at one end a roller,
H, which is kept pressed against the cam
D by means of the spring
J. When the cam,
D forces the roller,
H outward, the opposite end of the rocking lever strikes the stem of the exhaust valve,
F and lifts this valve from its seat, at the same time enabling the admission valve,
E to close under the influence of the spring with which it is provided. Thus the movement of the lever in one direction under the action of the roller
H opens the admission valve, and the return movement under the influence of the spring
J opens the exhaust valve, the latter also being fitted with a spring, as shown.
The admission chamber, as already stated, is provided with air ports,
b, which communicate with the external air through the passages,
a. The gas chamber,
K, on the other hand, communicates with the source of gas supply and has small ports governed by a lift valve,
c. Let us suppose now that an explosive charge of gas and air is being compressed in the cylinder end,
A. A small portion of the compressed charge will escape through a narrow groove into the port v, and pass from there through the port i into the chimney,
N. where it is ignited by the gas flame from
R. The flame of the ignited mixture passes back into the port v, but the fineness of the groove m prevents it from passing into the cylinder end,
A. When the time of igniting the charge in the cylinder has arrived, the cam C permits a quick outward movement of the piston valve,
P, first closing the port,
i by a small valve controlling it, and afterward opening the small end of the port,
v by the completion of the out-stroke of the piston valve P. The flame is thus first shut in, and then put in free communication with the combustion chamber
A, effecting ignition of the charge. The pressure in the combustion chamber, acting through the piston-valve
P upon the three-armed rocking lever
L, tends to keep the valve which controls the opening,
i tight upon its seat.
/fig. 51.jpg) Fig. 51—Detail of Starting Gear for Large Rollason Engines |
For starting large engines, the arrangement shown in Fig. 51 is used. A separate hand pump,
Q, is connected with the gas supply pipe, provided with check valves, so that a sufficient quantity of gas may be pumped into the combustion chamber to form an explosive mixture. To effect ignition of this mixture, the igniting device is provided with a releasable catch,
S, Fig. 51, to hold it in the non-igniting position after the crank has turned the centre. If the mixture were burning in the passageway,
v, the release of the catch,
S will cause ignition and explosion of the contents of the engine cylinder.
/fig. 56.jpg) Fig. 56—Valve Gear Detail of Captaine Engine |
In the smaller sizes of engine, the vertical engine, for example, the special igniting valve is not used, and the two-armed rocking lever controls simply the admission and exhaust valves, the tube igniter being always in direct communication with the end of the engine cylinder. The engine shown in Fig. 56 is one of two indicated horse-power. The horizontal design is turned out in sizes to meet the demand.
/fig. 52.jpg) Fig. 52— Captaine Oil Engine |
| /fig. 53.jpg) Fig. 53— Double Cylinder Captaine Launch Engine |
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/fig. 54.jpg) Fig. 54— Elevation of the Captaine Engine |
| /fig. 55.jpg) Fig. 55— Vertical Section of the Captaine Engine |
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An example of what is being done in Germany in the way of petroleum engines is afforded by the Capitaine engine shown in elevation and vertical section in Figs. 54 and 55. This engine is now being introduced into England by Mr. L. Tolch, of Liverpool.
/fig. 57.jpg) Fig. 57—Oil Pump of Captaine Engine |
The engine works on the Otto cycle. Oil is taken through a pump at
K, Fig. 54, and is forced into the vaporizer,
D, Fig-55. This vaporizer is kept hot by a flame from the lamp.
C. The latter is provided with a long tube which bends back upon itself, and ends in a burner cone. The flame plays on the lamp tube as well as on the vaporizer, and in this way the petroleum is converted into vapor before it reaches the burner cone. The ignition tube,
F also stands in the flame, and is made incandescent for the purpose of firing the charge, which is compressed within it on the second stroke of the piston. In the latest form of the engine, however, the use of the ignition tube has been abandoned, and the charge is fired by the heat of the vaporizer alone. On the first stroke of the piston air enters through the pipe,
B and inlet valve,
A, while the contents of the vaporizer are drawn out by admitting air at its end through the valve
C.
The exhaust valve and the oil pump are both operated by an eccentric. As they are required to move only at each alternate revolution, the mechanism shown in Fig. 56 is introduced to throw the eccentric rod in and out of engagement. The eccentric rod is pivoted to a slipper working in a guide; to this slipper is pivoted a crosspiece,
S with two arms. These arms work in conjunction with two fixed shoulder pieces striking them in succession. If with the parts in the position shown, the cross-piece were to rise it would operate the bell-crank,
M. As it neared the end of its travel one of the arms would strike the right-hand shoulder, tilting the cross-piece, so that on its next stroke it would miss the bell-crank. The left shoulder piece could then restore the cross-piece to its old position, and on the next stroke the bell-crank would be moved.
The bell-crank,
M works the lever,
L, one member of which raises the exhaust valve,
O, Fig. 55, while the other operates the pump, Figs. 54 and 57. The oil enters the tube at
V by natural pressure, and through the small aperture at the bottom of the bucket,
S, ascends up to the non-return valve,
H. On pressing the pump rod,
W, upward, the conical top point closes the bottom hole of the bucket,
S and carries the bucket before it, thus forcing the oil through the non-return valve,
H, through
T into the sprayer valve,
C, of the vaporizer. On letting go the rod,
W, the non-return valve, the bucket, and rod will be pressed down by springs to their original position shown in Fig. 57. All parts of the pump can be easily got at after slacking the top screw and removing the traverse. The capacity of the pump is regulated by screwing up or down the nut
a, thus limiting the stroke of the rod
W, which is securely screwed to the nut
b. When an engine of this kind is fitted to a launch, the pump is a suction and delivery pump of similar design, thus enabling the engine to pump oil from a tank below the pump. The vertical arm of the bell-crank ends in a detent which can be engaged by a corresponding detent,
N, Fig. 54, on a rod connected to the governor. The governor is carried in the flywheel, and transmits its motion through the boss to a sliding collar between the wheel and the bearing. A bell-crank and a rod connect the collar to the detent. The admission of oil is thus regulated by the governor according to the needs of the engine.
The operation of the engine is as follows: Explosion takes place with the piston on the top centre, after previous admission of oil-gas and air; the consequent impulse drives the piston down. On the upstroke the eccentric opens the exhaust valve and the burnt gases escape, the same movement of the eccentric also causing the feed pump to inject oil to the vaporizer. On the next down-stroke there is admission or suction of oil-gas and air; on this down-stroke and the next, the eccentric vibrating piece "misses," and on the upstroke the explosive charge is compressed, and when the piston is at top centre there is ignition and impulse. We thus have during two revolutions, impulse, exhaust, admission of fresh charge, and compression. The exhaust pipe is connected to the chamber marked
J in Fig. 54;
Q and
P in Fig. 55 are pipes leading from and to the water jacket surrounding the cylinder.
/fig. 58.jpg) Fig. 58—Single Cylinder Captaine Launch Engine |
During the early part of last year a launch was on trial at Chester, England, fitted with one of the Capitaine engines, a friction gear being used for reversing or letting the engine run idly with the propeller shaft at rest. The products of combustion from the cylinder were led to an exhaust chamber under a thwart, and from there were discharged under water. To the eccentric was attached a lever which worked a small pump. The latter circulated cooling water around the cylinder. An oil supply was carried in a tank in a bow chamber. The launch was thirty-five feet long by six feet ten inches beam by two feet six inches
draught, and could comfortably carry about fifty passengers. The engine developed, as a maximum, six and one-half horse-power, and gave a speed of about eight and one-half knots an hour. The weight of the engine complete was about 2000 pounds. On the European continent launches propelled by these Capitaine motors are extensively used, especially at Hamburg, where a comparatively large number are at work.
/fig. 59.jpg) Fig. 59—The “Trusty” Engine |
The "Trusty" petroleum engine, built by Messrs.
Weyman & Hitchcock, Limited, of Guildford, England, is shown in Fig. 59, the illustration representing a view of a double-cylinder engine, though the firm make also a single cylinder engine. Both types work on the four-stroke, or Otto cycle. In the double-cylinder engine, it will be noticed, the cranks are set together, and one impulse is
thus obtained at every revolution, the cylinders acting alternately. Ordinary, refined oil of commerce is used in the engine. The whole outfit is made up of the engine proper, a small oil pump, and a vaporizer, the last being arranged at the end of the cylinder. The oil is poured into a small tank, which is separate from the engine and can be placed in any convenient position in the engine room.
From this tank the oil passes to the pump through a small pipe, the pump being controlled by the governor. The requisite amount of oil is thus pumped into the vaporizer, and the vapor is drawn into the working cylinder during the suction stroke, mixing, in the cylinder, with a suitable proportion of air to make an explosive charge. Ignition of the charge is effected by an ordinary tube igniter kept hot by means of a small blow pipe flame.
/fig. 60.jpg) Fig. 60—The Brayton Petroleum Engine |
The Brayton petroleum engine, shown in Fig. 60, has already been illustrated and described in a separate article in an earlier number of this magazine, but is here again incorporated for the sake of convenience and completeness. The illustrations, while showing one of the older types of Brayton engines, used with very good results in the United States, perfectly represent the principles of operation.
The engine, as indicated by its name, belongs to the general class of petroleum engines, but in it no attempt is made to gasify or to vaporize, or even to heat the petroleum spray. The oil is finely divided—atomized in fact—in a large quantity of air, and is flashed into flame instantly. The combustion resembles that of flour dust or coal dust, suspended in the air, and which is so rapid that it constitutes an explosion. The combustible material is divided into infinitely small particles, and each particle is surrounded with an ample supply of oxygen, to which it exposes a surface, which is very great in relation to its bulk. Under these conditions combustion is exceedingly rapid, and spreads from particle to particle with amazing celerity. The oil is burned suspended in air; its combustion is complete, and is not impaired or delayed by metallic surfaces on which deposit can accumulate. The method of ignition is entirely novel. As the oil is not admitted till the moment of explosion, there is no question of “timing” valves, or of attaining a certain degree of compression before the charge can be fired. A brilliantly incandescent surface can be maintained in the cylinder all the time, ready to ignite the first drop of oil that comes in contact with it. To do this, advantage is taken of the well-known phenomenon of flame-less combustion, which is often shown on the lecture table, and but seldom found in practical work. A jet of air laden with hydrocarbon vapor is made to impinge continuously on a coil of platinum wire, which has been previously heated, and as long as the jet is continued the platinum is maintained at a glowing temperature within the cylinder.
The engine works on a modification of the Otto cycle. Explosion, exhaust, suction, and compression follow each other in the usual order, but the suction is a suction of air only (not gas and air), and the compression, also a compression of air only. Further, the exhaust valve is held open during the early part of the compression stroke to “ scavenge" the products of combustion out of the clearance space, and to replace them by air. As the oil is sprayed into the compressed air in the cylinder it requires a blast of high-pressure air to effect its entrance. This air is obtained from a pump, which also supplies air to the incandescent burner, a pressure of eighty pounds to the square inch being employed for this purpose.
/fig. 61.jpg) Fig. 61— Sectional View of the Brayton Engine |
| /fig. 62.jpg) Fig. 62— Sectional View of the Brayton Engine |
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A sectional view of the engine is given in Fig. 61, while Fig. 62 shows some of the details. The general appearance of the engine is that of an inverted beam engine, the beam being enclosed within the bed, and having a connecting rod at each end of it. From an intermediate point in the beam is worked the small pump which supplies the compressed air for spraying the charge and for maintaining the firing light. This pump is connected by a pipe to the cylinder head, shown on an enlarged scale in Fig. 62. The pipe,
A, together with the oil supply pipe,
B, discharges into a chamber, the bottom of which is closed by a valve,
C. When this valve is lifted, the oil is driven violently down the pipe, and through the circumferential cuts at its lower end, into the clearance space of the cylinder. The oil is finely divided by the action of the blast and is driven out at several different levels in minute particles.
The igniting device,
E is placed near to the sprayer
D. The former consists of a tube in the end of which there are coils of platinum wire. These are separated from a packing of asbestos,
F by a perforated steel disc and a plate of wire gauze. A fine bore tube connects the firing device with the auxiliary oil reservoir G in which the oil is kept at a constant level by a float. Air from the pump is admitted to this reservoir by the pipe,
H; part of it goes direct to the platinum burner through the adjustable cock,
J and part through the device,
K. This latter consists of a perforated vessel having an internal pipe, the lip of which is below the oil level, so that oil and air are driven upon it in spray to the asbestos pad,
F. The heat of the cylinder continually vaporizes the petroleum in the asbestos, and insures it being carried forward in gaseous form to the platinum coils. In order to effect the preliminary heating of the platinum, there is provided opposite to it a door
L with a glass-covered aperture in its centre. This door is opened, and a torch is inserted by which the platinum is raised to a red heat.
The oil pump,
M, Fig. 61, is operated by an eccentric driven by one to two gearing from the crankshaft. The exact length of stroke of this pump is determined by a wedge, which occupies a position in a slot between the ends of the eccentric-rod and of the pump plunger. When the engine is running above the normal speed, the wedge is raised by the governor; when it is running below the normal, the wedge is lowered and the stroke of the pump is nearly equal to that of the eccentric. A hand crank is provided, Fig. 60, by which the pump can be worked before the engine is started. On the same shaft with the eccentric is a cam for operating the oil inlet valve,
C, and the exhaust valve,
M. the former being opened when the left-hand end of the lever above it is raised, and the latter when it is depressed. The exhaust valve, as already stated, is opened at each revolution. It first evacuates the greater part of the products of combustion, and next it allows part of the air to blow through to scavenge the clearance space. This air is admitted by an automatic valve in the piston, Figs. 61 and 62, which opens as soon as a partial vacuum is formed in the cylinder. This position is chosen for the valve because the air can enter with little disturbance of the hot products of combustion, which congregate above, and can then sweep them completely out of the cylinder. To start the engine, the door L is opened and a torch of asbestos soaked in paraffin is introduced and placed beneath the burner
E. When this is properly heated the torch is withdrawn and the door closed. A charge of oil is then injected by hand and the flywheel turned. On the compression stroke an explosion should occur, after which the engine runs without further attention. The cylinder is, of course, water-jacketed in the usual way.
Information Sources
- Cassier's Magazine, V4, Jun 1893 pgs. 144-158