KerbLarge illustration(106 kB)
Large illustration(106 kB)
The top surface should always be tooled or axed whenever it has worn smooth and slippery, as a slip from a kerbstone often causes a very bad fall to a pedestrian.
Setting kerb requires a very experienced hand, for as it is set dry great care must be shown, or it will sink, turn slightly over, or move even months after it has been set. In addition to this it is heavy stuff to handle, but unless the line is accurate both as regards level and contour, the appearance will be exceedingly bad. Of course the skillet line and boning rods are freely used in setting kerb, but even with these helps one mason will set kerb in a pleasing manner, whilstanother, with even more care, does not seem able to make it appear graceful.
Deep and narrow kerb should be bedded on good clean river gravel, and beaten into its place with hard blows from a heavy wooden setting maul or beetle weighing not less than 50 lbs.
Broader and shallower kerb should be bedded on concrete.
In addition to granite, kerbing is also made of Endon or Yorkshire stone, limestone, and for brick pavements a kerb specially made of the same material is generally used; it is also, though not often in this country, constructed of wood, old railway sleepers being used for the purpose. In the more rural districts grass sods are used with good effect for gravel paths.
It is difficult to estimate the cost of kerbing, as local questions must interfere, carriage of the material and value of labour entering so largely into the question.
Mr. Codrington[110]states that “A limestone kerb about 1 foot deep and 4 inches wide costs from 2s.6d.to 3s.6d.per lineal yard, and a channel 10 inches wide by 6 inches thick rather more.
“Granite kerbs 12 inches wide by 9 inches deep, 6s.6d.to 7s.per yard run.
“Granite channel 12 inches wide by 6 inches deep, 4s.6d.per lineal yard.
“A channel 12 inches wide, formed of granite cubes 4 inches by 7 inches, costs about the same.”
I have found that granite kerb 6 by 12 inches could be fixed “in situ” at 3s.3d.per yard run, and 8 by 12 inches at 4s.6d.per lineal yard.
Granite channelling composed of 3 courses of granite pitchers 6 by 8 inches, costing 5s.6d.per lineal yard.
Limestone channelling 15 inches in width by 3 inches in depth, costing 3s.per lineal yard.
A paved channel, gutter, or water table is of the greatest use to a roadway, besides adding greatly to its appearance. Without such a channel the haunches of a road become sadly damaged by the wash of the surface water, which is sometimes so extreme as to undermine the kerb and cause it to fall out.
These channel gutters are made of different materials for macadamised roads, granite setts laid in the direction of the gutter being the best. A channel gutter should not be less than 18 inches wide, so that if made with ordinary 3-inch setts, 6 courses will be necessary; they should be bedded on gravel and well grouted in with lime or cement grouting. Sometimes granite slabs 18 inches wide by 3 or 4 inches thick are used and make an excellent gutter, they are however liable to tip under heavy loads. Limestone slabs can also be used in roads of light traffic with advantage.
In streets paved with granite setts, wood blocks or asphalte, the same material is used for the channelling, the setts or blocks being however bedded in line with the channel instead of transversely as in the street itself.
The channel gutter should take the slope of the roadway and the granite kerb should show from 3 to 5 inches above it. At paved crossings it is well to keep them level with the kerb so that pedestrians may step off the path on to the crossing without any drop, or if there is any water in them at such points, it is a good plan to let the edge of the crossing drop rather suddenly towards the kerb, so that the ordinary stride of the pedestrian carries him on to the level.
Gulley gratings or buddle holes should be placed along the line of channel at such intervals as may be found necessary. A great number of different forms have been from time to time introduced for this purpose, the objects to be considered being:
(1.) Sufficient area to carry off all the water.
(2.) Not easily choked on surface by leaves or other debris.
(3.) Sufficiency of pit to retain all sand or road detritus and prevent it being washed into the sewer.
(4.) The least possible obstruction to the traffic.
(5.) Constructed so that the pit may easily be cleaned out.
(6.) Trapped so as to prevent the escape of sewer gas.[111]
(7.) The drain from it should be easily freed of any obstruction.
One of the best forms of gully pit is that manufactured by Messrs. Oates and Green of Halifax, as it meets nearly all the requirements which I have summarised as being necessary for this description of work. The following drawing will explain itself:
Gully pit
What is called a “buddle hole,” which is an opening under the kerb, has much to recommend it as giving a free unobstructed waterway and at the same time avoiding thenecessity of a grating in the street itself. The following drawing will explain the general features of this “buddle-hole:”
Buddle holeLarge illustration(92 kB)
Large illustration(92 kB)
A great number of different descriptions and forms of gully pits are shown in Mr. Baldwin Latham’s excellent book on sanitary engineering, to which I refer my readers for any further information upon this subject.
[110]‘The Maintenance of Macadamised Roads,’ by Thomas Codrington, p. 18.[111]In many towns the gully gratings are purposely in direct communication with the sewers, so as to act as ventilators.
[110]‘The Maintenance of Macadamised Roads,’ by Thomas Codrington, p. 18.
[111]In many towns the gully gratings are purposely in direct communication with the sewers, so as to act as ventilators.
At the present moment the question of lighting streets by electricity is gaining so much attention, that it must necessarily be first considered in connection with the subject of lighting streets: but to enter fully into all the details and comparative merits of electricity and gas as applied to street lighting would entail more space than can be afforded in this work. It may however be of some use, even under the present state of uncertainty, if I attempt to condense as much information upon this necessary part of a surveyor’s duty into as small a compass as possible. Nor must it be forgotten that electric lighting will not easily be adapted in old cities and towns, where, in addition to the main streets being narrow and crooked, there are few large open spaces suitable for intense lights, and there are numerous small courts and alleys which require lighting, and this for a long time to come will probably be effected with gas.[112]
Section 161 of the Public Health Act 1875 enacts as follows:
“Any urban authority may contract with any person for the supply of gas or other means of lighting the streets, markets, and public buildings in their district, and may provide such lamps, lamp-posts and other materials and apparatus as they may think necessary for lighting the same. . . .” (38 and 39 Vic. c. 55, s. 161.)
I do not propose to entertain the question of lighting where the gas works are the property of the corporation, but only to give information that may be of use where a contract has to be entered into between the corporation and a company. These contracts are based nearly always upon the length of time at which the public lamps are to be kept lighted, and may be summarised as follows:
(1.) The public lamps are lighted from sunset to sunrise every night throughout the year; this averages 12 hours per diem, or about 4000 hours per annum.
(2.) The public lamps are not lighted on the nights of full moon, nor for two or three nights before and after this period; the rest of the year they are lighted at sunset.
(3.) Similar to the preceding, except that the public lamps are not lighted during the five nights of full moon, the night after they are lighted for one hour and extinguished on the rising of the moon; this lighting increases from night to night about three quarters of an hour until the moon has entirely disappeared, when the lamps are lighted during the whole of the night for five consecutive nights. Then again on the appearance of the new moon the lamps are extinguished the first night for about an hour that the moon is visible, and this extension increases nightly about three quarters of an hour according as the moon appears until the period of full moon, the intention being to profit by every hour of the moon’s light.
By this arrangement the lighting is about 2000 hours per annum, instead of 4000 hours, when it is continued throughout the night during the whole of the year.
(4.) Sometimes, in addition to the foregoing, the lamps are not lighted at all during the summer months.
(5.) Occasionally the public lamps are extinguished at midnight all the year round, if not for the whole, for some portions of the district, it being assumed that all respectable citizens being in bed, no light is required.
(6.) In some cases every other lamp only is lighted in the summer months, and many other similar variations for the sake of economy may be practised.
(7.) The public lamps are sometimes supplied by gas through meters, which is then paid for at so much per 1000 cubic feet consumed.
Of all the above methods the first is undoubtedly themost satisfactory to the inhabitants, the urban authority, their officers, and the gas company; it is the least likely to introduce disputes, and although something may be saved by adopting the more parsimonious methods enumerated, it is found in practice that the first is the best.
In drawing up an agreement with the gas company to light the public street lamps for any length of time, the following points must be considered.
The company to provide a sufficient supply of gas of the full illuminating power and quality as provided by their Act.
Payment to be at so much per lamp, or per 1000 cubic feet consumed, or at per hour, or whatever may be determined on.
Payment to be made by urban authority for lighting, extinguishing, cleaning, repairing, etc., as may be agreed, such payments to be made quarterly, or at such times as may be agreed upon.
The hours or times throughout the year during which the lamps shall be lighted to be determined by a table, every lamp to be fully lighted within one hour of the time named, and not extinguished before that named for extinguishing. The consumption of the gas to be regulated and determined by Sugg’s or Borradaile’s street lamp governors, or such other mode as is agreed upon.
The company to keep the governors and burners in repair, and also the lanterns, at a fixed sum per lamp per annum.
The company to light and extinguish, and keep all lanterns clean, and all pipes, valves, etc., in repair.
The company to keep the lamp posts etc., properly painted after they are fixed by the urban authority. Lamps may be shifted or fresh lamps erected by the urban authority, on their paying the cost.
The company not to be compelled to supply gas to lampswhich are beyond a certain distance of their existing mains, without compensation.
A certain pressure of gas must be maintained, to be ascertained by water gauges fixed at certain public places, or at such points as may be determined.
Any lamps burning under size or out, shall be immediately attended to by the company. A deduction in payment for gas by the urban authority to be made if neglect can be proved. An arbitration clause is necessary for this or other matters that may be disputed, and also a clause for determining the agreement upon notice being given.
In supplying gas to the public lamps by meter, either wet or dry meters may be employed, and these are fixed either in the lamp posts themselves or under the footpath. Sometimes each lamp has a separate meter, but in the generality of cases one meter fixed to a lamp gives the average of gas consumed by ten or a dozen of its fellows at the same level, and in the same neighbourhood. The difficulties arising from this system are:
(1.) The liability of the meters to get out of repair, especially in times of severe frost, or by vibration of traffic.
(2.) The first cost of providing and fixing the meters, and subsequent cost of repairs.
(3.) The trouble and cost of inspection and keeping the accounts.
And it is found that by employing either “Borradaile’s,” “Sugg’s,” or other regulators the consumption of the gas can be readily adjusted to consume from 3 to 6 cubic feet per hour, according to the requirements of the situation of the lamp.[113]
Lamp posts and lanterns are of innumerable sizes, shapes, and patterns, but the following hints in connection with them may be of some service.
The lamp must not only be ornamental by day, but useful by night.
The light must not be placed either too high or too low.
The post must not be too clumsy so as to interfere with the pedestrian traffic, nor too fragile so as to be easily broken if driven against. Bracket lamps have advantages in these respects, and also in the very important one of throwing no downward shadow,[114]as well as being cheaper.
The lantern should be made with the lightest possible amount of metal frame compatible with sufficient strength, the angle bars should be very narrow to avoid shadow, trap doors of perforated zinc or glass should be provided at the bottom for the admission of the torch, and a good outlet at the top is essential for the escape of the heated air. Flat glass is much cheaper and easier of repair than curved. The top of the lantern should be furnished with a reflector cover, otherwise a large percentage of the light is lost: this is very observable on approaching a large city, by the glare which is thrown upwards. Some hundreds of different patterns of lanterns for street lamps have been designed from time to time, and it is not necessary, nor have I space, to describe them.
The burners should have steatite tips and be of varying size to suit the requirements of the locality, the regulators which I have previously mentioned must be kept in good repair. A lever tap is indispensable with the torch for lighting, as well as the trap door or opening in the bottom of the lantern through which the torch is inserted.
Each public lamp post should be legibly numbered, andthe surveyor should keep a register in his office of all the public lamps in his town.
In order to determine the distance apart of the public lamps in a street, it must be remembered that the intensity of light is directly proportional to the illuminating power of the light, and inversely proportional to the square of the distance of the light, if unreflected. For instance, the illumination of any point between lamps may be arrived at by adding all the quotients obtained by dividing the illuminating power in standard sperm candles of each lamp, by the square of its distance in yards from the point.
Thus a point midway between two lamps of 15 candles each, 20 yards apart, would be reckoned thus:
X =15100+15100= ·30
In this country, the rule has generally been adopted that public street lamps burning 5 cube feet per hour of 15 candle gas should not be placed at a greater distance than 60 yards apart, the average distance in most English towns being about 40 yards.
On this question, the following interesting particulars by Monsieur Servier will be of special interest.[115]
It appears to M. Servier that up to the present there has been too much straining after intensity, with insufficient care for the object of obtaining a proper quantity of light uniformly spread over the surface of the ground. The paper in question is therefore intended in the first place to elucidate this latter subject, so as to determine beforehand the necessary intensity for luminous centres, gas or electric, and also their height from the ground and distance from each other required to produce a certain effect. With this purpose M. Servier proposes to determine for any point of the road-surface, bythe law of the squares of the distances, the intensity of light, in terms of the Carcel standard, which is spread at that point by one or more lights of given power. Representing these intensities by proportional ordinates, the extremities of these ordinates form an irregular surface, and the volume contained between this surface and that of the roadway represents a specific value equivalent to the total luminous intensity distributed over the soil. In default of a better term, M. Servier calls this a volume ofcubic Carcels, a cubic Carcel being the intensity of a Carcel (9·5 standard candles) multiplied by a square mètre of surface. The different cases capable of being valued in this manner are as follows:
1. A burner consuming 140 litres (5 cubic feet nearly), and of 1·1 Carcels (10·45 candles) illuminating power, placed at the height of 3 mètres (9 feet 6 inches). This burner gives at the foot of the lamp-pillar a maximum intensity of 0·122 Carcel (1·159 candles), and at 10 mètres (32·8 feet) away the illuminating power is reduced to 0·01 Carcel (0·095 candle). The distance of 20 to 30 mètres kept between the street lamps, even in the best-lighted towns, is therefore excessive, for these should not be more than 13 mètres (14 yards) apart in order to obtain between them the minimum illuminating power of 0·05 Carcel (0·475 candle), sufficient for enabling passengers to read.
2. The second case is that of a burner consuming 1400 litres (50 cubic feet nearly) of gas, with an illuminating intensity of 14 Carcels (133 candles), placed at the height of 3·20 mètres; this being the class of burner fixed in the Rue du Quatre Septembre. The intensity of light at the foot of the lamp-pillar is 1·367 Carcels (13 candles nearly), and to obtain the light of 0·05 Carcel (0·475 candle) already mentioned as the least intensity enabling one to read, a point must be fixed in a circle of 16 mètres radius from the lamp as a centre. Taking now a group of six lamp-columns, three on each side of the street, and overlapping, as in the Rue duQuatre Septembre, it will be found that the distribution of light is defective. The most brilliantly lighted point at the foot of the column has an intensity of 1·367 Carcels (13 candles), or more than triple that of the darkest point, which has an intensity of 0·5 Carcel (4·75 candles) at 4·58 mètres distance.
3. A lamp of 50-Carcel (475-candle) power, gas or electric, fixed at the height of 8 mètres (26·24 feet). The illuminating intensity at the point vertically under the light is reduced to 0·7 Carcel (6·65 candles); but the light of 0·5 Carcel (4·75 candles) is to be found in a circle of 6 mètres radius from this point. It will therefore be observed thatthe distribution of light over the ground is better in proportion as the luminous centre is higher; but conversely also,the amount of light thrown on the ground is greater as the luminous centre is lower. It consequently results that the power of the light and its height should be determined in every case with reference to the effect desired. The method shortly described shows that, in the case of the lighting of the Rue du Quatre Septembre, the mean amount of light per square mètre of the roadway is 855décicarcel-cubes, the best lighted parts having an intensity of 1·62 cubic Carcels, and the darkest portions an intensity of 0·50 cubic Carcel.
M. Servier has examined the question of lighting a street 20 mètres wide and one or more kilomètres long, with the condition that the illumination of the ground shall present a mean determinate quantity of light per square mètre, or a given intensity at the darkest points. Some interesting results are thus obtained. Thus, by substituting for the 14-Carcel (133-candle) lamps in the Rue du Quatre Septembre, burners of 50-Carcel (475-candle) power, with the condition of giving the same intensity of 0·5 Carcel (4·75 candles) to the darkest points, a quantity of light more considerable than before will be required. That is, a greater number of Carcels (3000 as against 1848 per kilomètre in length) will be necessaryin the larger burners than were required in the original smaller lamps. It is therefore imperative, in order that the lighting shall be equally economical, that the unit of intensity—the Carcel or candle power—shall be less costly in a lamp of 50 Carcel (or 475-candle power) than in the smaller lamps. By fixing lamps of 50-Carcel (475-candle) power in the centre of the street, instead of along the side walks, maintaining the condition of giving the light of 0·5 Carcel (4·75 candles) in the darkest parts of the thoroughfares, it is found that the pillars must be 8 mètres high and 20 mètres apart. The best-lighted part of the road would then have the intensity of 1 Carcel (9·5 candles), and would therefore be only twice as brilliantly lighted as the darkest corner; the mean quantity light per square mètre would be 755décicarcel-cubes.
Lastly, the same method of lighting has been applied to the “ordinary,” as distinguished from the “luxurious” lighting of the public thoroughfares, assumed to be 20 mètres wide, giving a light of 0·05 Carcel (0·475 candle) at the darkest points. With ordinary street burners consuming 200 litres (7 cubic feet) of gas per hour, and giving 1·72-Carcel (16·34-candle) power, it is found that the lamps should be 18 mètres (20 yards nearly) apart, the burners being 3 mètres (9 feet 10 inches) high. With burners of 14-Carcel (133-candle) power placed at the height of 3·20 mètres (10 feet 6 inches), the lamp-pillars would be 106 mètres (115 yards) apart. Or with lamps of 50-Carcel (475-candle) power placed at a height of 8 mètres (26·24 feet), the distance between the pillars may be increased to 270 mètres (494 yards).
In the case of electric lighting M. Servier has studied two examples—the Jablochkoff candle, and an arc light (system not stated). The former is credited with the illuminating power of 16 Carcels (152 candles), and is fixed at the height of 5 mètres (16 feet 3 inches), on pillars 110 mètres (120 yards)apart. This would give a light of 0·65 Carcel (6·27 candles) at the foot of the pillar, and a minimum intensity of 0·05 Carcel (0·475 candle) midway between the lights. The arc light is purposely made exactly equal in computed efficiency to the larger Siemens burner of 50 Carcels (475 candles). In the matter of expense, however, using the data applicable to Paris, with 12-candle gas at 6s.6d.per 1000 cubic feet, M. Servier makes a striking comparison. The cost of lighting a kilomètre of road in the “ordinary” manner last described varies very little for the three classes of gas lamps—small, large, and very powerful—included in the calculation, and ranges from 3·33 frs. to 3·96 frs. per hour. The cost of the same work done by the Jablochkoff candle is estimated at about double, or 6·91 frs. per hour; and with the arc light the cost would be 4 frs., or still higher than with the most costly system of gas lighting, although less than the expense of the Jablochkoff electric light.
The following table will show the particulars of different lights so placed that persons may see to read ordinary print in any part of the street, which may be taken as then being a well-lighted street.
It must not be lost sight of, that the illuminating power of the gas in Paris is very low, and is thus fixed. Under apressure of 12 hundredths of an inch, gas burning at the rate of 4·05 cubic feet per hour (or 115 litres) shall give a light of 9·5 standard sperm candles (or a “Carcel” lamp burning 42 grammes of pure colza oil) per hour.
The competition which has been started by the electric lighting companies has given a great impetus to gas lighting. A large number of improved street gas lamp burners and lanterns having been invented and brought into general use, the following particulars with reference to some of those which were tried in the City of Exeter may be of use as a comparison.
Having thus far given a few facts upon lighting streets with coal gas, I will now turn to the question of lighting them by means of electricity, and in doing this the following points will be considered:
(1.) The motive-power to be employed in producing electricity and its applicability for the purpose.
(2.) The description of machinery to be employed.
(3.) The value of the light produced, and its adaptability to the requirements of any town.
(4.) The comparative cost of the electric light as compared with gas.
(1.) Whatever motive power is employed, whether water-power,steam or gas, it is essential that it should be steady and unfailing; steady, because the regularity and uniformity of the light depends upon the evenness of the speed with which the power works, and unfailing, because a stoppage means the immediate extinguishment of the lights: electricity, unlike gas, is not stored after manufacture, but is used as fast as it emanates from the producing power.[116]
Sensitive governors and careful bedding of the machinery greatly tend to lessen unsteadiness, and are points of considerable importance.
(2.) The machinery consists of the dynamo machines, the conducting wires and the lamps.
I will not here enter into the question of which is the best dynamo machine to employ, as to discuss the merits of them all would involve a large amount of space; but for this and other valuable information upon the subject of electric lighting I will refer my readers to Mr. Hedges’ excellent little book entitled ‘Useful Information on Electric Lighting,’[117]but the following points should be attended to. The dynamo machine should be fixed in a dry place, and not be exposed to dust or flyings, it should be kept perfectly clean, and its bearings well oiled, its coils and conductors should be perfectly insulated, and it should, where practicable, be fixed on an insulated bed. With regard to the wires, the following ‘Regulations for the prevention of Fire Risks arising from Electric Lighting,’ published by the Society of Telegraph Engineers and of Electricians, are given in full, as they leave nothing to be desired in the way of their careful selection and fixing:
“(7.) Every switch or commutator used for turning the current on or off should be constructed so that when it ismoved and left to itself it cannot permit of a permanent arc or of heating, and its stand should be made of slate, stoneware, or some other incombustible substance.
“(8.) There should be in connection with the main circuit a safety fuse constructed of easily fusible metal which would be melted if the current attain any undue magnitude, and would thus cause the circuit to be broken.
“(9.) Every part of the circuit should be so determined that the gauge of wire to be used is properly proportioned to the currents it will have to carry, and changes of circuit, from a larger to a smaller conductor, should be sufficiently protected with suitable safety fuses, so that no portion of the conductor should ever be allowed to attain a temperature exceeding 150° F.
“N.B.—These fuses are of the very essence of safety. They should always be enclosed in incombustible cases. Even if wires become perceptibly warmed by the ordinary current, it is a proof that they are too small for the work they have to do and that they ought to be replaced by larger wires.
“(10.) Under ordinary circumstances complete metallic circuits should be used, and the employment of gas or water pipes should in no case be allowed.
“(11.) Where bare wire out of doors rests on insulating supports, it should be coated with insulating material, such as india-rubber tape or tube, for at least two feet on each side of the support.
“(12.) Bare wires passing over the tops of houses should never be less than seven feet clear of any part of the roof, and they should invariably be high enough, when crossing thoroughfares, to allow fire-escapes to pass under them.
“(13.) It is most essential that the joints should be electrically and mechanically perfect. One of the best jointsis that shown in the annexed sketches. The joint is whipped around with small wire, and the whole mechanically united by solder.
wires
“(14.) The position of wires when underground should be efficiently indicated, and they should be laid down so as to be easily inspected and repaired.
“(15.) All wires used for indoor purposes should be efficiently insulated.
“(16.) When these wires pass through roofs, floors, walls, or partitions, or where they cross or are liable to touch metallic masses, like iron girders or pipes, they should be thoroughly protected from abrasion with each other, or with the metallic masses, by suitable additional covering; and where they are liable to abrasion from any cause or to the depredations of rats or mice, they should be efficiently encased in some hard material.
“(17.) Where wires are put out of sight, as beneath flooring, they should be thoroughly protected from mechanical injury, and their position should be indicated.
“N.B.—The value of frequently testing the wires cannot be too strongly urged. It is an operation skill in which is easily acquired and applied. The escape of electricity cannot be detected by the sense of smell as can gas, but it can be detected by apparatus far more certain and delicate. Leakage not only means waste, but in the presence of moisture it means destruction of the conductor and its insulating covering by electric action.”
The lamps may take either the “arc” form, or the “incandescent.” The former is produced by the electric current passing between carbon points, and requires considerable electrical pressure; they give a light of from 1500 to 4000 candle power; the mechanism of arc lamps has to be of the most delicate kind to ensure the proper distance of the carbon points being maintained. The lamps should be guarded by globes of frosted glass, not only to prevent incandescent pieces of carbon from falling, but to lessen the glare of the light. “Incandescent” lamps are of small size, giving a light of from 8 to 50-candle power, which is produced by the heating of a filament of carbon in a vacuum owing to the resistance caused to the electric current by this contraction of the conductor.
(3.) With regard to the value of the light produced, and its adaptability to the requirements of any town, it will be seen on reference to the opening of this chapter that at present considerable doubt exists as to its adaptability for general public lighting, and as each town varies in the length, straightness, and width of its streets, the number of its large squares or confined courts and alleys, the surveyor must use his own judgment as to the suitability of the light before recommending his corporation to adopt it.
As to the value of the electric light, there can be no doubt that a most brilliant and powerful light is produced by the voltaic arc: so brilliant indeed, as to render it necessary to screen it nearly always behind frosted or opalescent glass globes, the former being found to be much the best for many reasons.
As to the photometrical value of the light, some considerable difficulty has hitherto been experienced in obtaining accurate observations, principally owing to the peculiar colour of the electric light, and also from its fluctuating character; but these difficulties are being steadily overcome, and with a photometer mounted on a light frame with wheels,some excellent experiments have been made in the public streets upon the comparative values of different lights.
(4.) The last and really one of the most important questions remaining to be discussed is that of the cost of the electric light as compared with gas.
With reference to the cost of the electric light, the following table may be of use; it is compiled from an excellent paper on electric lighting, by Mr. James N. Shoolbred:[118]
Table of Comparative Estimates of First Outlay andof Working Expenses of some Systems of Electric Lighting.
Mr. Shoolbred has also given another table[120]of streetlighting which partly deals with the question of cost, it is as follows:
As to the comparison of cost between the electric light and gas, this has only, I believe, been properly estimated on the Thames Embankment, London, by Sir Joseph Bazalgette, the results of whose investigations upon this important point I shall givepresently; it has, however, been stated generally, and without contradiction, that arc lights can be produced of about 2000 candle power, with 1 HP at a cost of from 3d.to 6d.per candle per annum of 4000 hours, gas costing from 1s.9d.to 3s.6d.per candle according to the price of the gas.
Incandescent lamps cost 3s.to 4s.per candle per annum, as their life is short, and only 200 candle power can be got from 1 HP.[121]
The latest investigations into the comparative cost of lighting by gas and electricity upon the Victoria Embankment and Waterloo Bridge in London, show that the lighting as effected by 96 gas burners for an average of 12 hours burning all night, and 121 gas burners for 6 hours lighted after the electric lights are put out, together with the electric lighting 40 lights on the parapet of Embankment, and 10 on the bridge, costs 834l.for the gas and 663l.for the electric light per annum. Gas costing 3s.2d.per 1000 cubic feet showed a cost of nearly 1s.per hour for every 1000 candle power of light. The electric lights cost 1¹⁄₂d.per light per hour, which is stated to represent 5·66 pence per 1000 candle power of light; each electric light as now used, it is said, gives a photometric light of 265 candles, frosted glass globes being found to pass much more light than the opalescent globes.
These are by far the most important and reliable comparisonsthat have hitherto been made, and it will be seen that the cost is in favour of the electric light.
There is no doubt that the acme of all artificial lighting is the prolongation of the light of day, and whether this is proposed to be effected by electricity or gas, it should be the goal aimed at by all who make this question their study.