Part 7

Apart from the unsightly appearance of overhead wires, there are many reasons why any extended system of supply of electricity should be carried out by underground cables. It is true that there have been no accidents in this country due to electric light wires falling, owing to the care bestowed on their insulation and erection; on account of the heat generated by the passage of the current through the leads no snow can accumulate on them, and therefore they are not subjected to the extra weight which destroyed so many of the telegraph and telephone wires in the last snow storm. Overhead electric light wires are exclusively used by the largest electric-supply company in London, and it is probable that, without further legislation takes place, other companies will shirk the expense of an underground system; and even a more dangerous method of running cables than that which has been condemned in the principal cities of the United States will become not the exception but the rule. In the city of New York the process of conversion of the present overhead to an underground system is a fact about to be accomplished to a very great extent at least, in the near future. Since July, 1887, the Western Union Telegraph Company have occupied the conduits, which have been constructed and laid with some 500 miles of wire; also the Metropolitan Telephone and Telegraph Company have 1000 miles of wire in the subways; and the Edison Illuminating Company, whose conductors were laid in the trench at the time of construction, has more than 1000 miles of underground cable. The plan adopted is to build conduits of section, as in Fig. 30, which shows the subway in course of construction, with man-hole opening and exposed ends of conduits. The single tube at top is for distribution between man-holes, and some wires are shown entering the vault on the right from the service box in the foreground. The conduits are of various types; creosoted wooden tubes are placed in creosoted wooden casings; wrought-iron pipes are sometimes laid in asphaltic concrete with creosoted wooden box; another arrangement is to be of composition blocks on concrete, and cover them with brick—or wrought-iron pipe is lined with cement, and laid in hydraulic cement concrete and cased with creosoted plank. About 85 per cent. of all the conduits have been constructed on this plan, the interior diameter of the pipes being 2½ inches.

Fig. 31 shows how the street arc lighting wires are taken, also a branch for house use, out of the man-holes, which are placed at each street crossing. For the cleaning purposes and for drawing the cable through the conduits, these must be laid practically straight.

Fig. 32 illustrates a method proposed by Mr. Kenneth Mackenzie, which is somewhat similar to the system of conduit which, used at Tours for the past two years, has been found most efficient for the high potential supply mains to the transformers. The troughs would be about 4 ft. long and 15 in. deep, having spigot and socket joints at the ends like ordinary water pipes. Transverse pieces of wood, or preferably slate, would rest upon projections, and would support the mains, and a cover recessed as shown would make the conduit fairly water-tight; drain holes would be provided, and the branches to houses led off through glands in the side of troughs. The American plan is, doubtless, the best, as there is no space for moisture to collect in the conduits; but Mr. Mackenzie’s system is well worth trying, and has the advantage of being much cheaper in first cost.

The Edison plan is to place two solid conductors in a tube which is filled up solid with an insulating material, suitable bends and offsets being supplied, so that the tube containing the two conductors can be buried in the ground like a gas-pipe. The system is very largely used both in the United States and in Continental cities; but it is doubtful whether the protection would suffice in our towns, where the streets are already at the mercy of the gas and water companies, whose workmen, with a single blow of a pick, might perforate the tube, and cause a dangerous short circuit.

THE INTERESTS OF GAS COMPANIES AS TO ELECTRIC LIGHTING.

The policy of gas companies with regard to electric light has, with few exceptions, been a state of indifference to the progress of things electric, with contempt for a rival whose opposition is not sufficiently powerful to be appreciated. The chairman of a well-known gas company stated, what is undisputed,—that the introduction of electric arc lights was accompanied by an increased consumption of gas in the immediate neighbourhood where these lights are used; but it is very doubtful whether this will be the case when incandescent lights are generally supplied. The introduction of these lights into any business district would mean the displacement of at least as many burners as there are electric lamps; and this reduction not only means loss of income, but also loss by interest on plant which is not kept at work to the capacity for which it was designed. The question suggests itself, “Are existing gas companies more favourably situated for furnishing electricity than any one else?” There are many reasons in favour of the supposition that the directors of gas companies have at the present time an opportunity of acquiring almost as complete a monopoly of lighting by electricity as they have with gas. As regards central-stations, everything is in their favour; there is generally some spare ground for the machinery, waste heat could be utilised, and a cheap fuel in the shape of coke is ready to hand. They have greater facilities for breaking up streets without danger of troubles arising with the local authorities, and if the Gasworks Clauses Acts, which authorise their existence, tie them down to one illuminant, a very little expenditure would enable them to enlarge their powers. In many towns the shareholders are local men who wish to use the electric light, but cannot favour its introduction because they think it would tend to smaller dividends or lower quotations for their shares; if, however, a scheme was promoted either by the gas company, or, if that was impossible, if the directors interested themselves in a separate electric light undertaking, the security which the gas and water investments command would, no doubt, cause a sufficient number of local subscribers to come forward and make even a small installation a paying concern. The Imperial Continental Gas Association have already taken up the supply of electricity in Vienna, and are likely to extend this new branch of their business to the other cities in which they hold gas concessions; also in the United States the growing opposition of the electric light companies is being seriously discussed, and already several gas companies are installing electric light plants.

It is not at all probable that the scare which caused such a drop in the value of gas shares when the electric light first appeared will be repeated, but the present high price of gas shares cannot be maintained. Kerosene lamps have been for some time a far greater rival to gas than electricity. The cheapening of petroleum, which is now shipped in bulk to this country in tank steamers, will cause the consumption to increase, and enable the oil to be supplied at a price so that it can be used in petroleum-engines, and give a motive power which will be found to be far more economical than the gas-engine. The latest development of petroleum-engines is that shown by Messrs. Priestman at the Royal Agricultural Society’s Show at Nottingham. The engine in external appearance is like the Otto gas-engine, but uses the ordinary “paraffin oil” of commerce, which has a high flashing point. The oil is simply put into a closed tank, and on the top of this, air is forced which drives the petroleum into a chamber heated by the exhaust from the engine, where it is partially vaporised and led into the cylinder with sufficient air to cause it to ignite by means of an electric spark.

The report of the trials with a 5 horse-power engine show that a brake horse-power was obtained for 1·7 lb. of oil, or at 6½_d._ per gallon for 1·4_d._ per horse-power per hour; with the Spiel engine the cost is stated to be 0·8_d._ per horse-power per hour.

Any serious reverse to the gas industry would cause a great pecuniary loss to a large number of investors. The paid-up and borrowed capital devoted to the manufacture and supply of gas in the United Kingdom exceeds £56,000,000, of which above £36,000,000 appertain to the companies and the remainder to the local authorities, whose receipts in respect of their gas undertakings last year exceeded £4,400,000.

The corporation of Bradford, who are owners of the gasworks, have wisely foreseen that it is better to keep the electric light in their own hands, and are now about to erect a central-station, and will lay underground wires; the amount sanctioned for this preliminary installation is £20,000.

THE LUCIGEN LIGHT.

A few remarks on this method of obtaining light from the combustion of crude petroleum may be added, as the light has been put forward as a cheaper and better substitute for the electric arc. The Lucigen light is produced by burning creosote oil, tar oil, or other heavy hydro-carbons, by means of compressed air in a special form of lamp, and consists of a cylinder at the side of which a steam donkey compressing pump is mounted, or in a more recent form known as the Wells’ light, no separate air compressor is used, but, instead, the pressure is obtained from the water mains or from a small force pump. The cost is stated to be 3_d._ per hour for 2,500 candle-power, requiring three gallons of oil per hour, but is in reality at the present time double this owing to the price of the oil, which, under the most advantageous circumstances, costs on average 2_d._ per gallon. At the Forth Bridge these lights have been found of use in illuminating open spaces, but have not supplanted the electric arc lights which are universally employed for the lighting of the works and the interior of the shops. The disadvantages are the noise, the oil shower which pervades the vicinity of the light causing timber staging to be highly inflammable, and the difficulty of preventing water from entering the burner, a few drops sufficing to extinguish the light. The use of the Lucigen light is, therefore, very limited, and it is probable that, in situations where shadows from the arc light are found to be objectionable, large incandescent electric lamps, which are supplied up to 1,500 candle-power, would meet the case; or, failing these, petroleum could be burnt in lamps similar to those used in lighthouses with greater safety, and at not much increased cost, than the compressed-air system.

USEFUL NOTES.

To ascertain in what direction the electric current is flowing through any wire by means of a pocket compass:—

A current flowing from _south_ to _north_ will always deflect the needle to the west, providing the wire in which the current flows is _over_ the instrument.

The word S. N. O. W. expresses this—south north over west; and should be remembered.

_Another simple plan_ is to hold the outstretched right hand over the compass; then, if the current flows in the direction of the wrist to the fingers, the needle will move towards the thumb.

To find the direction of the current in the wire of an electro-magnet:

Place the palm of the hand on the coil with the fingers parallel to the wires: the thumb will point to the _North Pole_ if the current is flowing as in previous rule towards the fingers. Conversely: if the _North Pole_ is known, the fingers will point to the direction of the current when placed parallel with the wires, with the thumb pointing to the North Pole.

If no compass is available, take two pieces of lead and place a few inches apart in a pot containing dilute sulphuric acid, scrape the lead clean, and join a piece of wire to each and connect to poles to be tested. After current has passed a short time one piece of lead will become brown, the other grey; trace the former to the dynamo cable, and this is the positive, and should be marked with a + or be painted red for future distinction.

_Incandescent Lights or Glow Lights._

The number of lights required to illuminate any room would vary very much, according to the style of decoration and position of the lamps. As a rule, a similar number of glow lamps are required as there would be gas burners. The former give a much higher standard of illumination, which, curiously enough, is generally expected with electric lighting on account of the purity of the atmosphere when the full light is being used, which is not the case with gas.

One 16 candle-power lamp will light an area of about 8 feet in diameter at 8 feet above ground; in ordinary situations allow, one lamp for 38 square feet.

_Arc Lighting of Works._

External.—56. 2,000 CP. arc lights will illuminate 160,000 square yards, or one for each 2,800 square yards.

Internal.—43. 2,000 CP. arc lights will illuminate 31,500 square yards, or one for each 730 square yards.

_Approximate Cost of Electric Light, Museum._

Arc lighting, 2/5 gas; with interest, ⅔. Incandescent, ⅔ gas; with interest, 4/3.

_Motive Power._

Compound engine 2 lbs. of coal per indicated horse-power per hour.

Good single-acting engine 3 to 6 per indicated horse-power per hour.

An indicated horse-power can be obtained in a compound engine from 20 lbs. of steam per hour.

A good boiler evaporates 9 to 10 lbs. of water per lb. of coal.

From 21 to 28 cubic feet of gas are required in a gas-engine per indicated horse-power per hour.

_Incandescent Lamps._

In practice allow 9-60 watt 16 CP. lamps per indicated horse-power of engine.

_Mem. for Wire Running._

Leads to the left or “low,” “_light coloured_.”

Returns to the right or “raised,” “_red_.”

_English and French Measures._

Millimetre = 0·039 inches 1 mill = ·0254 millimetres. Centimetre = 0·393 ” 1 inch = 2·5399 centimetres. Decimetre = 3·93 ” 1 foot = 3·3480 decimetres. Metre = 39·37 ” 1 yard = ·91439 metres. Cubic metre = 35·32 cubic feet or 1·31 cubic yards.

ELECTRICAL MEASUREMENTS.

The Paris Congress Units (1884) are now universally adopted and consist as follows:

_Electro-motive Force, and Potential_ (E).—The Volt. _The legal volt is ·926 of the E. M. F. of a Daniell’s cell, which for rough purposes may be taken as a volt._

_Resistance_ (R).—The Ohm. The legal ohm is now represented by the resistance of a column of mercury of a square millimetre in section at the temperature of zero centigrade 1·062 metres long.

_Current_ (C).—The Ampère. This is the strength of current sent through a wire having the resistance of 1 ohm at the E. M. F. of 1 volt.

_Quantity_ (Q).—The Coulomb. It is the quantity of electricity given by an ampère in a second. One coulomb decomposes ·00142 grain of water.

_Heat or Work_ (W).—The Joule, or Volt-Coulomb, is the work done by 1 coulomb in 1 ohm. The work done by any current per second is obtained in ergs by the product of the current into the electro-motive force producing it or W = CE or W = C²R. The Erg is the C. G. S. unit of work.

_Power_ (P).—The Watt, 1 ÷ 746 of a horse-power, employed in doing 1 joule of work in 1 second.

HP, or the Horse-power, is found by dividing C E by 746, thus (CE)/746 or (C²R)/746 = HP.

See also explanation of terms.

ELECTRICAL TABLE OF THE BIRMINGHAM WIRE GAUGE FOR PURE COPPER.

+---+-----+-----+-------+-------+---------+--------+--------+--------+ |B. |Diam.|Diam.|Area in|Circum.| Pounds | Feet | Feet | Ohms | |W. | in | in |Square | in | per | per | per | per | |G. | In. | mm. |Inches.|Inches.| Mile. | Pound. | Ohm. | 1000 | |No.| | | | | | | | Feet. | +---+-----+-----+-------+-------+---------+--------+--------+--------+ | 1 |·3 |7·62 |·070686|·94248 |1444·0087| 3·662 |8706·843| ·1148 | | 2 |·284 |7·21 |·063347|·89221 |1291·8699| 4·0988|7803·51 | ·1282 | | 3 |·259 |6·58 |·052685|·81367 |1074·5697| 4·9262|6490·09 | ·1540 | | 4 |·238 |6·04 |·044488|·74770 | 907·3683| 5·850 |5580·01 | ·17007| | 5 |·22 |5·59 |·038013|·69115 | 773·045 | 6·83 |4681·1 | ·2136 | | 6 |·203 |5·16 |·032365|·63774 | 657·205 | 8·02 |3985·7 | ·2509 | | 7 |·180 |4·57 |·025447|·56549 | 517·493 | 10·20 |3134·8 | ·3190 | | 8 |·165 |4·19 |·021382|·51836 | 434·861 | 12·14 |2633·7 | ·3797 | | 9 |·148 |3·76 |·017203|·46495 | 349·853 | 15·10 |2119·9 | ·4719 | |10 |·134 |3·40 |·014103|·42097 | 286·651 | 18·44 |1737·0 | ·5757 | |11 |·120 |3·05 |·011309|·37699 | 229·997 | 22·95 |1392·9 | ·7179 | |12 |·109 |2·77 |·009331|·34243 | 189·763 | 27·82 |1149·4 | ·8700 | |13 |·095 |2·41 |·007088|·29845 | 144·144 | 36·63 | 873·1 | 1·1454 | |14 |·083 |2·11 |·005411|·26075 | 110·035 | 47·98 | 665·3 | 1·503 | |15 |·072 |1·83 |·004071|·22619 | 82·790 | 63·77 | 501·5 | 1·9941 | |16 |·065 |1·65 |·003318|·20420 | 67·478 | 78·25 | 408·7 | 2·4466 | |17 |·058 |1·47 |·002642|·18221 | 51·3163|102·89 | 310·8 | 3·2176 | |18 |·049 |1·24 |·001886|·15394 | 38·3486|137·68 | 232·3 | 4·3052 | |19 |·042 |1·07 |·001385|·13195 | 28·1741|187·40 | 170·6 | 5·8599 | |20 |·035 | ·89 |·000962|·10995 | 19·5677|269·83 | 118·5 | 8·4381 | |21 |·032 | ·81 |·000804|·10053 | 16·3574|322·79 | 99·1 |10·094 | |22 |·028 | ·71 |·000616|·08796 | 12·5242|421·58 | 75·8 |13·185 | |23 |·025 | ·63 |·000491|·07854 | 9·9845|528·82 | 60·5 |16·539 | |24 |·022 | ·55 |·000380|·06911 | 7·7299|683·06 | 46·8 |21·357 | +---+-----+-----+-------+-------+---------+--------+--------+--------+

ELECTRICAL RESISTANCE OF COPPER WIRE IN FRENCH MEASUREMENTS.

+-------+------------+------+-------------+------------+----------+ | B.W.G.| Diameter | Area |Circumference| Metres | Kg. | | No. | in | in | in | per | per | | |Millimeters.| mm. | Millimeters.| Kilogramme.| Metre. | +-------+------------+------+-------------+------------+----------+ | 1 | 7.62 | 45.6 | 23.9 | 1ᵐ.95 | 0ᵏ.514 | | 2 | 7.21 | 40.8 | 22.6 | 2.78 | 0.360 | | 3 | 6.58 | 34 | 20.7 | 3.33 | 0.300 | | 4 | 6.04 | 28.7 | 19 | 3.95 | 0.253 | | 5 | 5.59 | 24.5 | 17.6 | 4.61 | 0.217 | | 6 | 5.16 | 21 | 16.2 | 5.43 | 0.184 | | 7 | 4.57 | 16.4 | 14.3 | 6.90 | 0.145 | | 8 | 4.19 | 13.8 | 13.1 | 8.20 | 0.122 | | 9 | 3.76 | 11.1 | 11.8 | 10.20 | 0.098 | | 10 | 3.40 | 9.1 | 10.7 | 12.50 | 0.080 | | 11 | 3.05 | 7.3 | 9.6 | 13.50 | 0.074 | | 12 | 2.77 | 6 | 8.7 | 18.87 | 0.053 | | 13 | 2.41 | 4.6 | 7.6 | 24.80 | 0.0403 | | 14 | 2.11 | 3.5 | 6.63 | 32.40 | 0.0309 | | 15 | 1.83 | 2.63| 5.75 | 45.10 | 0.0232 | | 16 | 1.65 | 2.14| 5.18 | 52.90 | 0.0189 | | 17 | 1.47 | 1.70| 4.62 | 69.40 | 0.0144 | | 18 | 1.24 | 1.21| 3.90 | 94.30 | 0.0106 | | 19 | 1.07 | 0.9 | 3.36 | 135.10 | 0.0074 | | 20 | 0.89 | 0.62| 2.80 | 181.8 | 0.0055 | | 21 | 0.81 | 0.51| 2.54 | 212.8 | 0.0047 | | 22 | 0.71 | 0.39| 2.23 | 285.7 | 0.0035 | | 23 | 0.63 | 0.31| 1.98 | 364 | 0.0028 | | 24 | 0.55 | 0.24| 1.73 | 465 | 0.00215 | +-------+------------+------+-------------+------------+----------+

+-------+------------------------------+------------+--------+ | B.W.G.| Resistance in Ohms | Kilogrammes| Metres | | No. +-----------------+------------+ per | per | | | per Kilogramme. | per Metre. | Ohm. | Ohm. | +-------+-----------------+------------+------------+--------+ | 1 | 0.00073515 | 0.000377 | 1360 | 2652 | | 2 | 0.00116760 | 0.000420 | 860 | 2379 | | 3 | 0.00168165 | 0.000505 | 595 | 1980 | | 4 | 0.00232260 | 0.000588 | 430 | 1700 | | 5 | 0.00322700 | 0.000700 | 310 | 1430 | | 6 | 0.00452319 | 0.000833 | 220 | 1200 | | 7 | 0.00731400 | 0.00106 | 137 | 945 | | 8 | 0.01025000 | 0.00125 | 98 | 802 | | 9 | 0.01581000 | 0.00155 | 63 | 646 | | 10 | 0.0237500 | 0.00190 | 42.20 | 527 | | 11 | 0.0318600 | 0.00236 | 31.40 | 424 | | 12 | 0.0539682 | 0.00286 | 18.60 | 350 | | 13 | 0.0932480 | 0.00376 | 10.70 | 266 | | 14 | 0.160380 | 0.00495 | 6.26 | 202 | | 15 | 0.294954 | 0.00654 | 3.40 | 153 | | 16 | 0.430077 | 0.00813 | 2.30 | 123 | | 17 | 0.73564 | 0.0106 | 1.35 | 94.5 | | 18 | 1.33906 | 0.0142 | 0.75 | 70.4 | | 19 | 2.60743 | 0.0193 | 0.38 | 51.9 | | 20 | 5.05404 | 0.0278 | 0.20 | 36 | | 21 | 7.04368 | 0.0331 | 0.14 | 30.2 | | 22 | 12.37081 | 0.0433 | 0.08 | 23.1 | | 23 | 19.6924 | 0.0541 | 0.05 | 18.5 | | 24 | 32.5500 | 0.0700 | 0.03 | 14.3 | +-------+-----------------+------------+------------+--------+

For Table of English Measurements see page 105.

EXPLANATION OF TERMS.

_Accumulator._—Another name for secondary batteries.

_Alternate Current Dynamo._—Produces currents which are alternately positive and negative.

_Amalgamation._—Zinc is protected from local action by having its surface coated with mercury.

_Ampère._—The Unit of current. A volt divided by an ohm. (See Electrical Measurements, page 104.)

_Ampère Meter._—An instrument used for measuring strength of current.

_Anode._—The positive electrode or pole of a decomposing cell, the wire or plate connected to the copper or other negative element of a battery. In electro-plating, it is usually the soluble pole of the metal to be deposited. (_v._ Cathode.)

_Arc._—The air space in which the electric light forms.

_Armature._—The keeper of a magnet: the part which closes the magnetic lines of the field-magnet, or the rotary part.

_Battery._—A combination of two or more voltaic cells coupled together.

_B. A._—British Association.

_Block Station._—A central-station for the supply of continuous buildings.

_Board of Trade Unit._—One thousand watt hours equals 10 ampères at 100 volts per hour, or 1·35 HP. working for one hour.

_Bobbin._—A coil of wire, or a number of such coils, generally so mounted that they can be rapidly revolved.

_Bridge (Wheatstone’s)._—An apparatus for measuring resistances by balancing the unknown resistance against one known and capable of adjustment.

_B. W. G._—Birmingham wire gauge.

_Candle-Power._—Term used to denote the amount of light as compared with a standard sperm candle, which is a spermaceti candle, burning at the rate of 2 grains per minute.

_Carbons._—The electrodes of arc lamps; the negative plate of a battery.