tgiO."] 



THE CIVIL KNGINEER AND ARCHITECT'S JOURNAL. 



399 



while the actual weight was 270, giving a preponderance of stability of 



3J to 1. , , • , 



Taking the middle division, ISO feet from the loo, the force of the wind 



was 37 ions, and this increased hy altitude to 31S lous; but (lie weight of 



the structure being 8S0, there still remains a preponderance of stability of 



2=^- to 1. 



At the base of the column the force was 03 tons, increased by height to 



no less than 630, while llie weight was ll"i70 tons, giving a preponderance 



of 24i to I, or rather less than the other points, and showing that the 



column could not overset but at the base. 



At the base of the pedestal, again, the stability was fully greater, being 



3J to 1. r , 1 



These results appeared very satisfactory, and the execution of the worlc 

 has striliingly conlirmed them. The stability and steadiness of the chini- 

 uey, even in high winds. Is remarkable; and while the old cliimney, which 

 is not half the altitude, is seen oscillating most sensibly by the naked eye, 

 it is difficult to detect the smallest movement in the other by accurate 

 telescopic observations with the theodolite. It is only in a violent gale, 

 such as occurred on November 7th, that even a slight degree of oscilla- 

 tion could be distinctly observed. And when we consider how very usual 

 it is for structures of this kind to oscillate in high winds(and even some of 

 the lighthouses, which are of a more solid character, are not exempt from 

 it), it is a strong proof of the strength of the work. 



Drawings were then exhibited, and the comparative stability calculated 

 of the small gas chimney, and of several other chimneys here and in 

 I'rance, all which were considerably below the present, and the French one 

 pronounced by Fresnel as showing great hardiliood— also the relative pro- 

 portions and heights of some lighthouses; and lastly, a comparison was 

 made, and drawings exhibited and described of the great chimney of St. 

 Kollox, 455 feet in height, and consisting externally of a single cone taper- 

 ing from the base to tiie summit, but not quite regularly, 41 feet in diaincler 

 at the base, and 13 at the top. The walls are in five divisions, increasing 

 in thickness from top to bottom. 



Another source of danger to be guarded against in these chimneys is 

 the intense heat which often arises from the furnaces, and the powerful 

 draught of the chimney. As a protection, an interior tube or chimney is 

 generally built of brick standing clear of the outer chimney, and on which 

 the effects of intense heat may be expended before it reaches the main 

 exterior chimney. This is very eilectual, but sliU the heat is great in 

 issuing from the inner chimney, which should not be carried too high. 

 In the present case, the inner chimney, 13 feet diameter, and lined with 

 fire-brick, rises only 70 feet, and the walls of the chimney being then 

 35 inches thick, present great resistance ; but as an additional precaution, 

 he recommended near this part, hoops of iron, which have been carried at 

 intervals 'of 35 feet all the way up within, and inclosed by the brick- 

 work, so that they are not visible. 



The only point remaining to be considered, and to which Mr. B.'s atten- 

 tion was particularly called, was the expediency of protecting the build- 

 ing by a lightning conductor. He had formerly, when the old chimney 

 was erected, been consulted as to this, and considered it unnecessary, the 

 height being moderate, and doubts being then entertained of tlie efficacy 

 or expediency of such instruments. Much, however, has since been 

 added to our knowledge and experience on this subject, and on the bene- 

 ficial operation of conductors; so that he had no hesitation, the altitude 

 also being so much greater, in recommenrling it. But having requested 

 to be favoured with the views of a friend, and high authority, Professor 

 Faraday, he gave an extract from his letter as follows: — ''The conductor 

 should be of i-inch copper rod, and should rise above the top of the 

 chimney by a quantity equal to the width of the chimney at the top. The 

 lengths of rod should be well joined metallically to each other, and this is 

 perhaps best done by screwing the ends into a copper socket. The con- 

 nection at the bottom should be good ; if there are any pump-pipes at 

 hand going into a well they would be useful in that respect. As respects 

 electrical conduction, no advantage is gained by expanding the rod hori- 

 zontally into a strap or tube — surface does nothing, the solid section is the 

 essential element.* There is no occasion of insulation (of the conductor) 

 for this reason. A flash of lightning has an intensity that enables it to 

 break through many hundred yards ([lerhaps miles) of air, and therefore 

 an insulation of 6 inches or 1 foot in length could have no power in pre- 

 venting its leap to the brickwork, supposing that the conductor were not 

 able to carry it away. Again, six inches or one foot is so little that it is 

 equivalent almost to nothing. A very feeble electricity could break through 

 that barrier, and a flash that could not break through five or ten feet could 

 do no harm to the chimney." 



" A very great point islo have no insulated masses of metal. If, there- 

 fore, hoops are put round the chimney, each should be connected metal- 

 lically with the conductor, otherwise a flash might strike a hoop at a 

 corner on the opposite side to the conductor,and then on the other side on 

 passing to the conductor, from the nearest part of the hoop there might be 

 an explosion, and the chimney injured there or even broken through. 

 Again, no rods or ties of metal should be wrought into the chimney 

 parallel to its length, and, therefore, to the conductor, and then to be left 

 unconnected with it.'' 

 In answer to some further inquiry. Professor Faraday again writes : — 



* The ver; reverse of what was formerly held bj high authorities. 



" The rod may be close along the brick or stone, it makes no diiTerence. 

 There will be no need of rod on each side of the building, but let the cast- 

 iron hoop and the others you speak of be connected with the roil, and it 

 will be iu those places al least, as if there were rods on every side of the 

 chimney. 



" A three-fourth rod is no doubt better than a half-inch, and, except for 

 expense, I like it belter. IJut a half-incli has never yet failed. A rod at 

 Coutt's brewery has been put up li inch diameter; but they did not 

 mind expense. The Nelson Column in London has a half-inch rod — Ihree- 

 fonrths is better. 



'• I do not know of any case of harm from hoop-iron inclosed in the 

 building, but if not in connection with the conductor I should not like it ; 

 even then it might cause harm if the li;;htning took the end furthest from 

 the conductor." 



The rod was constructed nearly according to these directions, of 'J-incIi 

 copper, and the elfect of it was very remarkably exeinplilicd during the 

 progress of the work. It was carried up regularly along with the building, 

 and during storms, or a very electric slate of the atmosphere, the electric 

 fluid was distinctly perceived rushing down the rod, by a loud singing 

 noise given out by it, arising from a tremor or vibration into which it was 

 thrown, by a little play in the studs or eyes through which it passed in the 

 building, and during these times the workmen were by no means fond of 

 approaching too near it, but no harm ever occurred to any one from it. 



The work of the chimney was commenced by laying the foundation on 

 the 3id of June, 1S15, and during the course of that season the mason- 

 work of the pedestal was completed, and the work allowed to stand til 

 the spring. The brickwork of the shaft was commenced on the 2ad of 

 May, 1S46, and proceeded rapidly during the summer. The bricks and 

 all the materials were taken up in the inside by means of a steam-engine 

 working at the bottom, and winrling a rope over a b.irrel, and this passing 

 over a pulley on the top of the building, l!ie materials were raised with the 

 greatest facility ; and it was carious to observe from difl'erent parts of the 

 tower the work gradually rising, and the workmen sieadily going on, at 

 the great elevation to which they at last attained. A model was shown of 

 a very simple apparatus, by which the stage for the materials and timbers 

 was raised by successive lifts, as the building rose in height. 



The contractors for the mason-work of the stone pedestal were Messrs. 

 Gowan, and for the brick-work of the stalk Messrs. Bow, of Glasgow, to 

 whom much credit is due for the superior style in which they have finished 

 their work; and it may also he mentioned, that no accident or casualty of 

 any serious nature occurred during the execution of this great work. 



Several observations still remained to he made on Part II. as to the 

 draught of the chimney, but were deferred to another day, as well as 

 Mr. Taylor's paper, to give time for the distribution of the prizes for last 

 session. 



Thanks voted (o Mr. Buchanan. 



NffiTES OF THS JM02JTK. 



Sir John Rennie and Mr. Brunei, at the request of the parish 

 authorities, have made their report nn the failure of Warren's 

 Girder Bridge, over Joiner-street, London-bridge {ante p. 390), 

 which contains their joint and decided opinion,— that the bridge, 

 as constructed, was insufficient, ;ind ought not to be replaced by 

 one of similar construction. — j\Ir. Barloiv, the engineer of the rail- 

 way, has addressed a letter to tlie Times, stating that he entirely 

 disagrees with the above report; and that he does not consider the 

 principle of the bridge either incorrect or objectionable. We 

 advise Mr. Barlow not to kick over the traces; he had better keep 

 quiet and mal<:e the best of a bad business. ^Ye are very anxious 

 to hear the result of the testing of the bridge; we left our card 

 with ;Mr. Barlow's assistant at tlie time the experiment was being 

 made, and begged that he would favour us with the amount of 

 deflection for "every 10 tons' dead weight laid over two of the 

 girders, and tlie final result of tlie experiment. Altlioiigh tlie testing 

 took place tliree weeks since, we have not been favoured with any 

 particulars. If Mr. Barlow wishes to stand well in his profession, 

 we advise him not to conceal any similar information: he may rely 

 upon it that a fair statement does more good than any concealment. 



Portugal boasts of her first steam-engine. A tug, v.ith engines 

 from an Englisli factory at Oporto, has towfid a sliip over the bar 

 of the Douro. The Portuguese speak of Leing independent of 

 foreign aid in constructing engines. Save the mark ! 



The third number of Mr. Tinkler's ' Architectural Sketches in 

 Italy' is partly occupied with villa subjects, which will naturally be 

 of interest to his readers. Some of these villas are suited only to 

 the Roman climate and habits of life; but their picturesque 

 arrangements will afford sonie ideas for study here, and tiiey will 

 therefore be the more valuable, as tliey are suggestive without 

 admitting of direct copying. Some of the gateways, sketched 

 under the name of Fragments at Rome, are likewise of consider- 

 able interest. 



