1843.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



429 



It is contended, from experience, tliat granite pavement can be laid down, 

 so that the results will be superior to macadamizing, not only as regards 

 economy of construction and maintenance, and power in draught, but also 

 of the other qualities, with the single exception of noise, which, it is shown, 

 need not he so great a disadvantage as to warrant its rejection ; if the sets 

 be well dressed, and properly laid, on a sufficient substratum, and if the sets 

 are not used too broad, a sure foot-hold for the horse can at all times be 

 had, besides contributing more to the solidity of structure, than the broad 

 and shallow blocks so frequently employed. 



By experiment, it appears that wood is a more efficient and durable mate- 

 rial for paving, than stone of any description, and that it is capable of af- 

 fording all the qualities required (or our finest streets. In order to ascertain 

 the best position ot the fibre, for securing all the advantages which wood 

 can afford, a minute table is given of the results of experiments, during a 

 period of eighteen months, upon blocks with the fibre placed vertically and 

 horizontally, and leaning at the intermediate angles; from this it appears 

 that vertical blocks sustain less abrasion and less injury than those in any 

 other position. A sound concrete substratum, is held to be an essential 

 feature, in the successful application of wood for paving; and if blocks in a 

 vertical position, be laid down in a dry state, with close joints, the surface 

 and structure can be maintained, under any change of weather, in a condi- 

 tion to resist any amount of traffic and heavy loads. It is shown that cohe- 

 sion is not a fluctuating quality, for the blocks in the pavement are, in 

 reality, not liable to become wet and dry with atmospheric changes. In wet 

 weather they absorb as much moisture as they can contain, which increases 

 their volume, and from which moisture they are never after totally free, even in 

 the driest weather, as they still remain damp, and retain an excess of volume 

 over the dry state iu which they were originally laid down, more than suffi- 

 cient for supplying perfect cohesion under any change of the atmosphere. 

 It is also shown that wood does not produce mud and dust, and that slip- 

 periness is therefore foreign to wood pavement ; that its economy in main- 

 tenance, power in draught, cleanliness and comfort, are favourable recom- 

 mendations ; — and that wood is an efficient material for paving, whether 

 subjected to wet, dry, or frosty weather. 



Tables are then given, showing the results of the experiments in a con- 

 densed form, ami from which it appears, that, the power of traction being 

 in each 1001b., the weight drawn on a level macadamized road, is on an 

 average 27 cwt.; on a level granite pavement, 30J cwt. ; and on a level wood 

 pavement 54J cwt. 



" On the Ventilation of Lighthouse Lamps; the points necessary to be ob- 

 served, and the manner in which these have been or may be attained." By 

 Professor Faraday, L.L.D., Hon. Mem. Inst. C. E., &c. 



The author states that the fuel used in lighthouses for the production of 

 light is almost universally oil, burnt in lamps of the Argand or Fresnel con- 

 struction ; and, from the nature and use of the buildings, it very often hap- 

 pens that a large quantity of oil is burnt in a short time, in a small chamber 

 exposed to low temperature from without, the principal walls of the chamber 

 being only the glass through which the light shines ; and that these cham. 

 bers being in very exposed situations, it is essential that the air within should 

 not be subject to winds or partial draughts, which might interfere with the 

 steady burning of the lamps. 



If the chamber or lantern be not perfectly ventilated, the substances pro- 

 duced by combustion are diffused through the air, so that in winter, or damp 

 weather, the water condenses on the cold glass windows, which, if the light 

 be a fixed one, greatly impairs its brilliancy and efficiency, or, if the light be a 

 revolving one, tends to confound the bright and dark periods together. The 

 extent to which this may go, may be conceived, when it is considered that 

 some lighthouses burn as much as twenty, or more, pints of oil in one 

 winter's night, in a space of 12 or 14 feet diameter, and from 8 to 10 feet 

 high, and that each pint of oil produces more than a pint of water; or, from 

 this fact, that the ice on the glass within, derived from this source, has been 

 found in some instances an eighth, and even a sixth, of an inch in thickness, 

 and required to be scraped off with knives. 



The carbonic acid makes the air unwholesome, but it is easily removed by 

 an arrangement which carries off the water as vapour. One pound of oil 

 in combustion produces about 106 pounds of water and 2'86 pounds of car- 

 bonic acid. 



The author's plan is to ventilate the lamps themselves by fit flues, and 

 then the air inside the lantern will always he as pure as the external air, yet 

 having closed doors and windows, a calm lantern, and a bright glass. 



In lighthouses there are certain conditions, to which the ventilating ar- 

 rangement must itself submit, and if these are not conformed with, the plan 

 would be discarded, however perfect its own particular effect might be. 

 These conditions are chiefly, that it should not alter the burning of the oil 

 or charring of the wicks — that it should not interfere with the cleaning, 

 trimming, and practice of the lamps and reflectors — that it should not ob- 

 struct the light from the reflectors — that it should not, in any sudden gust 

 or tempest, cause a downward blast or impulse on the flame of the lamp — 

 that, if thrown out of action suddenly, it should not alter the burning ; and, 

 added to these, that it should perform its own ventilating functions perfectly. 



Lighthouses have either one large central lamp, the outer wick of which 

 is sometimes 3J inches in diameter, or many single Argand burners, each 

 with its own parabolic reflector. The former is a fixed lamp ; the latter are 



frequently in motion. The former requires the simplest ventilating system, 

 and is thus described : — 



The ventilating pipe or chimney is a copper tube, 4 inches in diameter, 

 not, however, in one length, hut divided into three or four pieces : the lower 

 end of each of these pieces, for about 1 J. inch, is opened out into a conical 

 form about 5i inches in diameter at the lowest part. When the chimney is 

 put together, the upper end of the bottom piece is inserted about \ an inch 

 into the cone of the next piece above, and fixed there by three ties or pins, 

 so that the two pieces are firmly held together; but there is still plenty of 

 air-way, or entrance, into the chimney between them. The same arrange- 

 ment holds good uit'n each succeeding piece. When the ventilating chimney 

 is fixed in its place, it is adjusted, so that the lamp-chimney enters about 

 half an inch into the lower cone, and the top of the ventilating chimney 

 enters into the cowl or bead of the lantern. 



With this arrangement it is found that the action of the ventilating flue, 

 is to carry up every portion of the products of combustion into the cowl; 

 none passes by the cone apertures, out of the flue into the air of the lantern, 

 but a portion of the air passes from the lantern by these apertures into the 

 flue, and so the lantern itself is in some degree ventilated. 



The important use of these cone apertures is, that when a sudden gust, or 

 eddy of wind, strikes into the cowl of the lantern, it should not have any 

 effect in disturbing or altering the flame. It is found that the wind may 

 blow suddenly in at the cowl, and the effect never reaches the lamp. The 

 upper, or the second, or the third, or even the fourth portion of the venti- 

 lating flue might be entirely closed, yet without altering the flame. The 

 cone junctions in no way interfere with the tube in carrying up all the pro- 

 ducts of combustion ; but if any downward current occurs, they dispose of 

 the whole of it into the room, without ever affecting the lamp. The venti- 

 lating flue is. in fact, a tube which, as regards the lamp, can carry everything 

 up, but conveys nothing down. 



In lighthouses with many separate lamps and reflectors, the case is more 

 difficult and the arrangement more complicated, yet the conditions before 

 referred to are more imperatively called for, because any departure from 

 them was found to have greater influence in producing harm. The object 

 has been attained thus : — A system of gathering pipes has been applied to 

 the lamps, which may be considered as having the different beginnings at 

 each lamp, and being fixed to the frame which supports the lamps, is made 

 to converge together and to the axis of the frame by curved lines. The 

 object is to bring the tubes together behind the reflectors, as soon as conve- 

 nient, joining two or more into one, like a system of veins, so that one venti- 

 lating flue may at last carry off the whole of the lamp products. It is found 

 that a pipe |ths of an inch in diameter is large enough for one lamp ; and 

 where, by junction, two or more pipes have become one, if the one pipe has a 

 sectional area, proportionate to the number of lamps which it governs, the 

 desired effect is obtained. 



Each of the pipes Jths of an inch in diameter, passes downwards through 

 the aperture in the reflector over the lamp, and dips an inch into the lamp- 

 glasses; it is able to gather and carry off all the products of combustion, 

 though, perhaps, still 2 inches from the top of flame, and therefore not in- 

 terfering in any respect with it, nor coming as a shade between it and any 

 part of the reflector : the flame and reflector are as free in their relation to 

 each other as they were befDre. Neither does this tube hide from the 

 observer or mariner, a part of the reflector larger than about li square inch 

 of surface, and it allows of a compensation to two or three times the 

 amount ; for, when in its place, all the rest of the aperture over the lamp, 

 which is left open and inefficient in the ordinary service, may be made effec- 

 tual reflecting surface, simply by filling it up with a loose, fitly formed, re- 

 flecting plate. 



At this termination of the ventilating flue an important adjustment is 

 effected. If the tube dip about an inch into the lamp-glass, the draught up 

 it is such that not only do all the products of combustion enter the tube, 

 but air passes down between the top edge of the lamp-glass and the tube, 

 going, finally, up the latter with the smoke. In this case, however, an evil 

 is produced, for the wick is charred too rapidly ; but if the ventilating flue 

 descends until only level with the top of the lamp-glass, the whole of the 

 burnt air does not usually go up it, but some passes out into the chamber, 

 and at such times the charring of the wick is not hastened. Here, there- 

 fore, there is an adjusting power, and it was found by the trials made, that 

 when the tube dipped about half an inch into the lamp-glass, it left the 

 burning of the lamp unaltered, and yet carried off all the products of com- 

 bustion. 



The power already referred to, of dividing a chimney into separate and in- 

 dependent parts, and yet enabling it to act perfectly as a whole, as shown in 

 the single central chimney, was easily applicable in the case of several lamps, 

 and gave a double advantage; for it not only protected the lamps from any 

 influence of down draught, but it easily admitted of the rotation of the 

 system of gathering flues, fixed to the frame sustaining the lamps and re- 

 flectors in a revolving lighthouse, and of the delivery of the burnt air, &c, 

 from its upper extremity into the upper immoveable portion of the flue. 

 This capability in a revolving light is essential, for in all, the support of the 

 frame-work is of such a nature, as to require that the upper part of the flue 

 should be a fixture. 



The author explains that it is as an officer of the Trinity House, and under 

 its instructions, that he entered into the consideration of this subject : that, 

 as to the central chimney, its action has been both proved and approved, 

 and that all the central lights arc ordered to be furnished with them; that 



