Part 62

“Pursuant to the instructions received from the Deputy Master to furnish you with my opinion on the relative merits of the electric and gas lights under trial at the Clock Tower, Westminster, I beg to submit the following report:—On the evening of the 1st ultimo I was accompanied by Sir F. Arrow (who kindly undertook to check my observations by his experience) to the Westminster Palace, where we met Captain Galton, R.E., Dr. Percy, and some gentlemen connected with the electric and gas apparatus under trial. I was informed that the stipulations under which the lights were arranged were, that they be fixed white to illuminate a sector of the town surface of 180°, having a radius of three miles. I first examined the Gramme magneto-electric machine, in use for producing the currents of electricity. This machine we found attached by a leather driving-belt to the steam engine belonging to the establishment. We then proceeded to the Clock Tower, where we found the electric lamp, at an elevation of 250 ft. The Wigham gas apparatus was placed at the same elevation, within a semi-lantern of twelve sides, about 8½ ft. in diameter, and 10 ft. 3 in. high in the glazing. Near the centre of the lantern were three large Wigham burners, each composed of 108 jets. After the examination of the apparatus, we proceeded to Primrose Hill, for the purpose of comparing the electric and gas lights at a distance of three miles. The evening, which was wet and rather misty, was admirably suited to our purpose, ordinary gas-lights being barely visible at a distance of one mile.”

The results of a photometric comparison of the electric and gas lights were as under, the machine making 389 revolutions per minute, and absorbing 2·66 horse-power; the illuminating power of the gas used being 25 candles, and the quantity consumed 300 cubic ft. per hour.

┌───────────────────────────────────────────────┬──────────┬──────────┐ │ │ Electric │Wigham Gas│ │ │ Light. │ Burner. │ │ │ │108 jets. │ ├───────────────────────────────────────────────┼──────────┼──────────┤ │Relative intensity of lights │ 945·56│ 370·56│ │ Or as │ 100 │ 39·19│ │Illuminating power in standard sperm candles as│ 3,066 │ 1,199 │ │ units │ │ │ └───────────────────────────────────────────────┴──────────┴──────────┘

“_Electric Light._—Total cost per session £174 5_s._ 0_d._, being equal to 5_s._ 7_d._ per hour of exhibition of the light. Details shown in the full report. Gas Light.—Total cost per session of one burner of 108 jets, £159 15_s._ 3_d._, equal to 5_s._ 1·4_d._ per hour of exhibition of light, and £296 3_s._ 4_d._, equal to 9_s._ 5·9_d._ per hour of exhibition of the light, when using three burners of 108 jets each. Details shown in the full report. It will be observed from the photometric measurements, before referred to, of the electric light and 108–jet gas burner, that in the case of the electric light we have at our disposal for distribution over the required area an illuminant radiating freely in space equal to 3,066 candles; with the gas light we have an illuminant radiating freely in space equal to 1,199 candles. It is to be remembered that in dealing with the small electric spark as the focus of a dioptric apparatus for distribution over the required area, the light can be more perfectly utilized than with the large gas flame of the Wigham burner, owing to its very small dimensions as compared with the latter. The relative cost and efficiency of the three modes of illumination may be summed up as follows:

┌──────────────────────────────────────────┬────────┬─────────────────┐ │ │ELECTRIC│ GAS. │ │ │ LIGHT. │ │ ├──────────────────────────────────────────┼────────┼────────┬────────┤ │ │ │ One │ Three │ │ │ │108–jet │108–jet │ │ │ │Burner. │Burners.│ ├──────────────────────────────────────────┼────────┼────────┼────────┤ │Cost of light per hour, in pence │ 67 │ 61·4 │ 113·9 │ │ Or as │ 100 │ 91·6 │ 170 │ │Cost of light per candle per hour in pence│ ·0219 │ ·0512 │ ·0317 │ │ Or as │ 100 │ 233·8 │ 144·7 │ │Cost of light from a dioptric apparatus │ ·00118 │ ·00310 │ ·00275 │ │ for fixed light per standard candle per │ │ │ │ │ hour expressed in pence │ │ │ │ │ Or as │ 100 │ 262·7 │ 233·1 │ └──────────────────────────────────────────┴────────┴────────┴────────┘

“Thus by adopting the electric light as a standard of intensity and cost, there is shown a superiority over the gas in intensity of 65·2 per cent. when using one 108–jet burner, and 27·1 per cent. when using three 108–jet burners. There is also shown a saving in cost per candle or unit of light per hour of 162·7 per cent. when using one 108–jet burner, and 133·1 per cent. when using three of these burners, forming a triform gas-light. It is further to be remembered that the triform gas-light actually represents the maximum power obtainable at present by gas; but no reference has been made to the power of increase capable in the electric light by the adoption of two magneto-electric machines. By having the machine and lamp in duplicate, as estimated, and which I consider a necessity to insure perfect confidence in the regular exhibition of the electric light, this light can be doubled in intensity during such evenings as the atmosphere is found to be so thick as to impair its efficiency. This double power would be obtained at the trifling additional cost of coals and carbons consumed during the time this increased power may be found to be necessary; this additional cost I estimate at 4_d._ per hour. With the arrangement proposed for the electric light, I consider this powerful illuminant, if manipulated by careful attendants, perfectly reliable: in proof of this I may state that the electric light at the Souter Point Lighthouse, on the coast of Durham, has now been exhibited two years and a half, and the light has never been known to fail for one minute.”

Fig. 278 represents one of the light-producing machines. The electro-magnets are excited by a portion of the currents they themselves produce, they retaining sufficient residual magnetism to develop the currents. There is a pair of current-collectors on each side. This machine weighs 1,540 lbs., its height is 3 ft., and width 2 ft. It will produce a light having the intensity of 500 Carcel lamps, which may be doubled by increasing the speed. Fig. 279 is another form which is also adapted for illuminating purposes, and, when made with fewer coils, for electrotyping purposes also. There are in this also two sets of current-collectors, and by means of a connecting cylinder (seen at the base of the machine) the currents can be combined for quantity and for tension as may be required. This machine is only about 2 ft. square, and it produces a light equal to 200 burners; but this may be increased, as the following table shows:

┌─────────────────────┬─────────────────────┬─────────────────────────┐ │Number of revolutions│Intensity of light in│ Remarks. │ │ per minute. │ Carcel Lamps. │ │ ├─────────────────────┼─────────────────────┼─────────────────────────┤ │ 650│ 77│No heating and no sparks.│ │ 850│ 125│No heating and no sparks.│ │ 880│ 150│No heating and no sparks.│ │ 900│ 200│No heating and no sparks.│ │ 935│ 250│A little heat, no sparks.│ │ 1,025│ 290│Heat and sparks. │ └─────────────────────┴─────────────────────┴─────────────────────────┘

The value of M. Gramme’s invention for electro-plating is proved by the fact of its adoption by Messrs. Christofle of Paris, whose electro-plating establishment is one of the largest in the world. This firm has no fewer than fourteen of these machines at work, and each is capable of depositing 74 ozs. of silver per hour. There is little doubt that the electric current will now soon be employed for reducing metals. Thus fine copper, which is worth 3_s._ or 4_s._ per lb., may perhaps be obtained at about the cost of ordinary copper; potassium, sodium, and aluminium at less than half their present price; and magnesium, calcium, and other rare metals at prices which will bring them into commercial use. The machine shown in Fig. 280 is intended for electro-plating and for general purposes: it supplies the means of readily and cheaply plating with copper, or with any other metal, such articles as steam pipes, boiler tubes, ship plates, guns, bolts, nails, marine engines, machinery, culinary vessels, cisterns, &c. The advantage of protecting iron or other material from corroding agents is obvious; and as iron coated with copper is available not only for useful, but also for artistic, purposes, as a cheap substitute for bronze, this invention will doubtless lead to a greatly extended application of bronzed iron in buildings and ornamental structures.

The machine well illustrates how mechanical work may be changed into electricity, and electricity caused to do work. The power required to drive the machine at a given speed is much less when no current is being drawn from it, than when the current is flowing. If the current from one machine is sent through the armature of another, the latter revolves, and may be made to do work. Thus _power_ may be conveyed to a distance by electricity, with only the loss caused by the resistance of the conducting wires. If, when two machines are thus connected, the direction of rotation in the first one be suddenly reversed, the armature of the second will almost immediately stop, and then resume its motion in the opposite direction. A very interesting experiment can be performed when the circuit connecting the two machines is made to include a certain length of platinum wire. When both machines are in motion, the platinum exhibits no heating effects; but if the second machine be stopped by an assistant while the rotation of the first is continued, the wire is raised to a red heat. In this way it is shown that motion, electricity, and heat are related to each other, and are mutually convertible; for on the stopping of the second machine, the electricity being no longer used up, so to speak, in producing motion, has its power transformed into heat.

The Gramme machine has also been ingeniously employed for railway brakes on some of the Belgian lines; and it is applicable to telegraphy, where the cost of zinc, acids, batteries, &c., is a considerable item. It is impossible to predict the many applications for manufacturing purposes which will be made of electricity, now a cheap, reliable, and convenient mode has been discovered of producing currents of any required strength. Though by no means the first or only machine by which mechanical force can be converted into dynamical electricity, it shows an immense advance on any former one in the regularity of the action, and in the capability of being driven at a very high rate of speed without the inconvenient accompaniments of the heating of the conductors and destructive sparks at the movable contacts. There can be no doubt of the importance of this machine for use in lighthouses, and for metallurgical and chemical purposes, and the inventor believes the time will come when all large ocean-going vessels will carry an electric light at the masthead. The light would be sufficiently powerful to show rocks or land five or six miles ahead, and an additional safeguard of incalculable value would be thus provided for those “that go down to the sea in ships, that do business in great waters.”

_ELECTRIC LIGHTING AND ELECTRIC POWER._

It was mentioned in the last section that the introduction of so convenient and reliable a means of producing electrical currents as the Gramme machine, would cause electricity to be largely applied for illuminating and other purposes. The Gramme machine was first made in 1870, and it attracted much attention, as the principle of combining the currents was quite different from that used in previous magneto-electric machines. In fact, the Gramme machine yielded quite unexpected results, and the principle employed in it opened a new field. The development that has taken place in the applications of electricity within the twenty years since 1870 has been truly marvellous. The electric light appears to have been first used in lighthouses about 1862, and the machines by which the current was produced were, in principle, combinations of a great number of Clarke’s machines (see page 509). One such machine was invented by Mr. Holmes, and was used for the illumination of the South Foreland Lighthouse in 1862. Another similar form of still earlier invention had been set up in Paris as early as 1855,—not, indeed, for the purposes of illumination, but for a project which failed. Its arrangement had been originally suggested by a Belgian physicist in 1849; and the machine of 1855, having received certain improvements, afterwards became very well known by the name of the _Alliance Company’s_ machine, or simply the _Alliance_ machine. It is represented in its improved form in Fig. 280_a_. Here ranges of steel horse-shoe magnets will be observed, each magnet weighing about 40 lbs. and made of six plates of tempered steel, held together with screws. Each of the eight rows of magnets contains seven, and thus sixteen poles are presented at uniform distances, arranged in circles. Carried on the central axle are six discs, which revolve between the circles of sixteen poles, and on the circumference of each disc are sixteen equidistant bobbins or coils of insulated wire, so that the whole of the sixteen coils are opposite to the sixteen poles at the same moment. The extremities of the wires at the coils are connected with proper adjustments for gathering up the currents, and by means of these the coils may be arranged either for tension or for quantity, like the elements of a battery (page 494).

Wilde’s machine, which has been mentioned in page 511, is shown in fig. 280_b_. It will be observed that this consists of a small machine, M, with permanent steel magnets, and the current from these circulates through the coils of the electro magnets, A B. The arrangement of the armatures, bobbin, commutators, etc., is the same in both cases. But as a speed of 2,500 revolutions per minute was needed, it was necessary to keep the bearings, T T, from heating by causing cold water to circulate through them. Mr. Ladd arranged a machine on the same principle as Wilde’s, by suppressing the permanent magnets, but availing himself of the _residual_ magnetism of the iron core to bring about the induction. A machine of this kind was shown at the Paris Exhibition of 1867, and people were quite astonished to see electrical power capable of producing a brilliant light developed by a small machine 2 ft. long, 1 ft. wide, and 9 in. high. But the great velocity of rotation, and the consequent heating of the bearings, left much to be desired before a really practical machine could be produced.

In the newest Siemens’ machine, represented in fig. 280_c_, the Gramme principle is made use of, as the revolving coil is of large diameter, and it consists of a copper cylinder, on which are wound a number of juxtaposed coils like those of a galvanometer. The revolving cylinder is surrounded by the poles of a system of electro-magnets excited by the whole of the induced current being passed through their coils. In a paper describing this machine, Siemens first made use of the term “dynamo-electric machine,” and this expression, contracted to the single word DYNAMO, has since been universally employed to designate machines of this kind. The modifications in the forms and arrangements of the different dynamos that have been invented in late years are endless, and every week patents are granted for further improvements and fresh combinations of the parts. It would be quite beyond the scope of this work to enumerate all the forms of the dynamo that have been favourably spoken of; but we shall content ourselves by adding a drawing of the Brush dynamo (Fig. 280_d_), which has been so largely used for electric lighting in the United States. In this dynamo we have a Gramme ring, but the number of coils on it is reduced to eight, the intervals being filled up with pieces of iron, and the ring revolves in a vertical plane between the poles of two double oblong electro-magnets, which are arranged with poles of the same name opposite to each other. The commutators shown in the nearer part convert the alternately reversed currents generated in the coils into a direct continuous one. They are formed with bundles of wires, as in the Gramme machine.

But the providing of a cheap and efficient source of current electricity, although an absolutely necessary step, would not have been capable of bringing about the present development of electric lighting, unless the appliances by which the current is made to manifest itself as light had not also been brought nearly to perfection. The conditions required to maintain a steady light from a current of electricity passing between carbon points have been already explained on page 497, and a representation of Dubosc’s electric lantern and regulator is shown. The regulator systems that have been invented since it became obvious that the light of the electric arc admitted of practical application on the large scale are very numerous. The earlier forms of regulator, which were used only for scientific purposes—such as lantern projections on screens, experiments on light, etc.—were complicated in their arrangements and uncertain in their action, for great variations in the light sometimes took place, and occasionally it would, indeed, be extinguished, and then again shine out as brightly as before. Nearly all the regulators that have come into use depend upon movements controlled by electro-magnetic actions produced automatically as the distance between the carbon changes. It would, however, lead us too far into the technicalities of the subject to explain minutely the mechanism of any particular form of the mechanical regulators, and the results depend so often upon the minute details, that it would be difficult to trace the action without a set of large and complete drawings. Perhaps the regulators that have been most used are those of Serrin, Siemens, Brush, Thomson, Houston and Edison. But nearly every inventor has produced different forms of his apparatus; Siemens, for instance, has patented eight or ten regulators. Fig. 280_e_ shows the mechanism of one of the last named inventor’s regulators, in which the two actions required for the separation and approach of the carbons are determined respectively by the vibrations of the rocking lever, M Y L, actuated by the electro-magnet, E, and the simple weight of the upper carbon-holder, A A. When the lamp is not in circuit, the lever, L, is thrown back by a spring, the tension of which is regulated by the screw, R, so that the catch, Q, is disengaged from the wheel, I. The train of wheels is then free to revolve by action of the rack, A, supporting the weight of the upper carbon, until the motion stops by the carbons touching each other. Now let the lamp be connected up, and the current will pass from C, through the electro-magnet, the mass of the apparatus, and return by the wire connecting the lower carbon-holder with Z. The carbon points will glow, but the magnet then attracting M moves the lever, L, the piece, Q, engages the wheel I, pushing it one tooth forward. But this movement of the lever establishes a contact at X, so that the current abandons the electro-magnet, to pass the shorter way, and M being no longer attracted, the lever is pushed back by the spring, the contact at X is broken, and the magnet being again excited the lever turns as before, and Q pushes I round the space of another tooth. These alternating actions succeed each other with great rapidity, and effect the separation of the carbons through the train of wheels acting on the racks. These movements continue until, in a second or two, the separation of the carbons has become so great, that the current passing through the electro-magnet is no longer able to operate against the weight of the upper carbon-holder, and this happens when an arc of proper size is produced, this required result being brought about by proper adjustment of the parts of the apparatus, marked by the letters R, K and X. But as the carbons are consumed, the increase of the length of this arc further weakens the current, until the spring attached to the lever, L, prevails over the attractive force of the electro-magnet on M, and thus withdraws the catch, Q, altogether, when the wheels being free to turn, the weight operates to bring the carbons nearer together, until, with the lessened resistance, the energy of the current is restored, and Q again comes into play to arrest the approximating movement. It may be seen, from the above explanation, that this lamp is automatic; in other words, when it has once been properly adjusted, it is lighted by merely completing the circuit. For fixing the carbons properly in their holders there are, of course, other regulating screws. How very nearly perfection the automatic regulation of the arc electric lamp has been brought by such contrivances as these, will be obvious to all who have noticed the steadiness that has been attained in all the modern installations.