« ElőzőTovább »
A choice remained to be made between at least differs from the Bell Rock, was found from first lo four different curves, which would each comply last to occasion much inconvenience. The sandstone with the conditions specified in Mr. Stevenson's of the Bell Rock is worn into rugged inequalities. conclusion—the logarithmic, the parabola, the con- The action of the sea on the igneous formation of choid, and the hyperbola. The logarithmic, Skerryvore has given it the appearance and the though not unfavorable to the condition of vertical smoothness of a mass of dark-colored glass, which pressure, was dismissed as clumsy; the parabola made the foreman of the masons compare the operdispleased the eye from its too rapid change near ation of landing on it to that of climbing up the the base ; the similarity between the conchoid and neck of a bottle. When we consider how often, the hyperbola left little to choose between them, by how many persons, and under what circumbut the latter obtained the preference. The shaft stances of swell and motion this operation was of the Skerryvore pillar, accordingly, is a solid repeated, we must look upon this feature of the generated by the revolution of a rectangular hy- spot as an obstacle of no slight amount. perbola about its asymptote as a vertical axis. Its The 7th of August, 1838, is noted as the first exact height is 120-25 feet ; its diameter at the day of entire worle on the rock. It consisted in base 42 feet, and at the top 16 feet. (p. 61.) The preparations for the temporary barrack, which in first 26 feet from the base are solid, and this por- this case, as in that of the Bell Rock, was contion weighs near 2000 tons. The walls, as they sidered a necessary preliminary, and was in most spring from the solid, are nine feet thick, and respects a copy of its predecessor. Little more gradually diminish to two. Mr. A. Stevenson than the pyramidal pedestal of beams for this considered himself safe in dispensing generally building could be accomplished before the 11th of with the system of dovetailing, which had been September—the last day of work for that season adopted throughout the building in the two pre--and this commencement was swept away in the ceding instances. By an improved construction night of the 12th of November :—a calamity of the floors of the chambers he also supplied the which mortified those whom it could not daunt nor place of the metal chains which Smeaton had discourage, and which only led to various imused to restrain any disposition to outward thrust proved devices for reconstruction. The quarries in the circle of masonry, and the copper rings by meanwhile had been busy in Tyree, but the exwhich the cornice of the Bell Rock building is perience obtained during this winter, 1838 and strengthened. The above are some of the princi- | 1839, of the gneiss-rock of that island led Mr. pal features of the differences suggested by study Stevenson to resort for further supply to the graniteand experience between the three works. We quarries of Mull. In specific gravity the gneiss must refer our readers to p. 63 for a diagram has a trifling advantage, but it is less fissile and which makes them sensible to the eye. The fol- far more uncertain in quality. Of the quantity lowing table, however, may be sufficient :- hitherto obtained in Tyree not more than one tenth
was found fit to be dressed as blocks for the tower.
The next important operation was that of excavating the foundation. This occupied the whole
of the working season of 1839, from the 6th of Eddystone 13,343 26
May to the 3rd of September. The gneiss held Bell Rock
23,530/ 42 Skerryvore
out stoutly against iron and gunpowder, and Mr.
Stevenson calculates the labor at four times that The last column shows the ratio which the which granite would have required. In the case height of the centre of gravity above the base of the Eddystone, Smeaton was compelled to folbears to the height of the tower.
low the shape of the rock, and to adapt his lower Those who have perused the “Diary' of Mr. courses of masonry to a sort of staircase of sucR. Stevenson's voyages to and fro, and long res- cessive terraces carefully shaped for the adjustidences in anchored vessels at the Bell Rock, will ment. The formation of Skerryvore enabled Mr. anticipate that much of the difficulty with which Stevenson to avoid this delicate and expensive prothe father had to contend was obviated in the case cess, and to mark ont a foundation-pit of 42 feet of the son by the application of steam-power to diameter, the largest he could obtain at one level navigation. The first year's operations at Skerry- throughout. This basin, however, required for its vore were, however, not assisted by this new aux- excavation the labor of 20 men for 217 days, the iliary. A steamer was advertised for, but the firing of 296 shots, and the removal into deep water river and harbor craft offered for sale were quite of 2000 tons of material. The blasting, from the unfit to encounter the seas of Tyree, and it was absence of all cover, and the impossibility of refound necessary to build a vessel for such rough tiring to a distance further in any case than 30 service, of 150 tons, with two engines of 30-horse feet, and often reduced to 12, demanded all possible
Mr. Stevenson found, as he con- carefulness. The only precautions available were ceives, compensation for the delay in the accurate a skilful apportionment of the charge and the knowledge of the reef and surrounding waters covering the mines with mats and coarse netting which constant trips in the Pharos sailing-vessel made of old rope. Every charge was fired by or of 36 tons procured for him.
with the assistance of the architect in person, and One peculiarity of the Skerryvore, in which it no mischief occurred. The operations of 1840 in
Base. lop. 68
15 133.5 59.380 42 16
1592 23.59 34.95
4.27 4.29 3.96
cluded the reconstruction of the barrack, in which, / weather, which sometimes made it impossible to though rather more pervious to wind and spray land a sufficient supply of materials on the rock, than what Mr. Robins in his boldest mood would and at other times made it impossible to use them. have ventured to designate a “desirable marine At such intervals the architect's anxiety was great villa," the architect and his party were content to for the safety of the stones deposited on the rock, take up their quarters on the 14th of May. “Here,” but which they had as yet been unable to move says the gallant chief,
beyond the reach of the surf. The loss or fracduring the first month we suffered much from the ture of any one of these would have occasioned much Hooding of our apartments with water, &c. On one delay. The discomfort of wet clothes, and scanty occasion also we were fourteen days without com- accommodation for drying them, after exposure to munication with the shore or the steamer, and during sleet and spray, was severe. And yet the granthe greater part of that time we saw nothing but deur and variety of the surrounding scene, comwhite fields of foam as far as the eye could reach, bined with the deep interest of the work in hand, and heard nothing but the whistling of the wind and the thunder of the waves, which was at times were sufficient not only to compensate for the so loud as to make it almost impossible to hear any tedium of occasional inaction, but, in the words one speak. Such a scene, with the ruins of the of the narrator, “to reconcile him to, nay, to make former barrack not twenty yards from us, was cal- him actually enjoy, an uninterrupted residence on culated to inspire the most desponding anticipations : one occasion of not less than five weeks on that and I well remember the undefined sense of dread desert rock." that flashed on my mind, on being awakened one
In addition to the magnificent phenomena of innight by a heavy sea which struck the barrack, and organic nature, an object of interest was afforded made my cot swing inwards from the wall, and was immediately followed by a cry of terror from the by the gambols of the seal, which is said by report men in the apartment above me, most of whom, of the neighboring islanders to attain a remarkable startled by the sound and the tremor, sprang from size in the neighborhood of the reef. There is their berths to the floor, impressed with the idea something to our apprehension very human in the that the whole fabric had been washed into the sea. seal. The voice, the expression of the eye, its
known affection for musical sounds, and its docilThis spell of bad weather, though in summer, ity, and even attachment to individuals, when well nigh outlasted their provisions ; and when at caught young, give it claims to better treatment length they were able to make the signal that a than it usually receives from man.
The greatest landing would be practicable, scarcely twenty-four living authority in matters of zoology has conjechours' stock remained on the rock.
tured that the strange animal seen from the DædaAs yet nothing of weight but iron and timber lus frigate was a seal of the largest (sea-lion) had been landed. The first trial of the landing species ; that it had probably been drifted into of heavy stones from the lighters, on the 20th of warm latitudes on an iceberg which had melted June was a nervous one. It succeeded, but diffi- away, and swimming, poor brute, for life,
had culty and hazard in this operation were of constant neared the strange object, the ship, with some recurrence; and, as the loss of one dressed stone faint original hope of shelter and rest for the sole would frequently have delayed the whole progress of its slipper. If Captain M'Quhae could admit of the building, the anxiety was incessant. Eight a theory which attributes to him and to his officers hundred tons of dressed stone were, however, depos- so large an amount of ocular deception, we are ited on the rock this season without damage. On sure he would share our regret at his inability to the 7th of July the ceremony of laying the foun- accommodate so interesting a stranger. The seals dation stone was performed by the Duke of Argyll, of Skerryvore made no such demand on Mr. Steattended by a party of relations, including the venson's hospitality. They enjoyed the surf which Duchess and Lady Emma Campbell, and many menaced him with destruction, and revelled in the friends.
luxuries of a capital fishing stationThe summer of 1840 was a stormy one, and it They moved in tracks of shining white ; required some habit to contemplate calmly, even And when they reared, the elfish light from the height of thirty feet, the approach of the Fell off in hoary flakes. Atlantic wave. The exhibition of its power was Perhaps, like the Ancient Mariner, he “ blessed more formidable during that period of ground swell them unaware ;” but thus he writes of them :which follows a protracted gale than amidst the violence of the actual storm. Cool and careful
Among the many wonders of the “great deep" observation Jed Mr. Stevenson to conclude that the is the agility and power displayed by the unshapely
which we witnessed at the Skerryvore, not the least height of an unbroken wave in these seas does not seal. I have often seen half a dozen of these aniexceed fifteen feet from the hollow to the crest; mals around the rock, playing on the surface or but this was magnified to thirty or forty in the es- riding on the crests of the curling waves, come so timation of less scientific watchers-some of whom close as to permit us to see their eyes and head, could scarcely familiarize themselves even by re
and lead us to expect that they would be thrown peated experiences of safety to the illusive ap- denly they performed a somersault within a few
high and dry at the foot of the tower; when sudpearance of imminent destruction. The greatest feet of the rock, and, diving into the flaky and trial of such a residence was doubtless the occa- wreathing foam, disappeared, and as suddenly reäpsional inaction resulting from the violence of the peared a hundred yards off, uttering a strange low cry, as we supposed of satisfaction at having caught served. The torch in Hero's tower, and the telea fish. At such times the surf often drove among graphic fire-signals so magnificently described in the crevices of the rock a bleeding cod, from whose the " Agamennon” of Æschylus, could hardly back a seal had taken a single moderate bite, leaving the rest to some less fastidious fisher.-P. 157. have failed in times anterior to the Pharos of Ptol
emy to have suggested the use of continuous In July, 1841, as the masonry rose to a height lights for the guidance of the mariner. In later which made the stationary crane difficult and even periods, when the coasts of France and Britain unsafe to work, that beautiful machine, invented were more frequented by the predatory northman for the Bell Rock, and which rises with the build- than by the peaceful merchant, and when the haring it helps to raise, the balance crane, was brought vest of shipwreck was considered more profitable into requisition with all the efficiency and success than the gains of commercial intercourse, it probdescribed in the narrative of the elder Stevenson. ably often appeared to the inhabitants of the With such aid the mass of masonry built up dur- seaboard more their interest to increase than to ing this working season amounted to 30,300 cubic diminish its dangers. It is related of one of the feet—more than double that of the Eddystone, and Breton Counts, St. Leon, that, when a jewel was somewhat more than that of the Bell Rock tower. offered to him for purchase, he led the dealer to a Such was the accuracy observed in the previous window of his castle, and, showing him a rock in dressing of the stones in the work-yards on shore and the tideway, assured him that black stone was in their collocation by the builders, that the gauged more valuable than all the jewels in his casket. diameter of each course did not vary from the cal- | The only modern work of consequence anterior to culated and intended dimension one sixteenth of an the Eddystone, cited by Mr. Stevenson, is the Tour inch, while the height exceeded that specified by de Cordouan, situated in the mouth of the Gaonly half an inch. Mr. A. Stevenson only does ronne some two leagues from Bordeaux, which in justice to his father in stating that much of the respect of altitude and architectural grandeur and comparative rapidity of his own work was due to embellishment remains, as Mr. Stevenson says, the the steam attendance at his command. No death noblest edifice of the kind in the world. Whether from accident or injury occurred during the entire that embellishment be as well suited to the subprogress of the work—but the loss of Mr. Heddle, ject-matter as the severer grandeur of the curvicommander of the steamer, who died of consump-linear towers of Smeaton and the Stevensons, may tion in the course of the winter, was probably due be questioned. Commenced by Louis de Foix, to exertion and exposure in that service. On A. D. 1584, in the reign of Henry II., and finished the 21st of July the last stones for the tower were in 1610 under Henry IV., it exhibits that national landed under a salute from the steamer. On the taste for magnificence in construction which at10th of August the lantern was landed. It was, tained its meridian under Louis XIV. The tower however, impossible to do more this season than does not receive the shock of the waves, being to raise and fix it, and cover it with a temporary protected at the base by a wall of circumvallation, protection from the weather and the dirt of sea- which contains also casemated apartments for the fowl for the winter.
attendants. Hence a construction in successive The summer of 1843 was occupied in repoint- stages and angular in the interior, consequently ing the joints of the building-a tedious operation less adapted for solidity, but more susceptible of conducted from suspended scaffolds—and in fitting decoration, than the conical, has for two centuries the interior. It was not till the 1st of February, stood uninjured. In this, as in our own light1844, that the light was first exhibited to mariners. houses, the inventions of science have been gradFor reasons most ably and minutely detailed in a ually substituted for the rude original chauffoir, or concluding chapter, the apparatus adopted was brazier of coal and wood, such as within memory identical in its general arrangements with that— was in use in the Isle of May. In the latter case in the main dioptric, but combining some of the it is supposed to have led to the destruction of two advantages of the catoptric system of illumination frigates, which mistook for it some kilns on the
—which had been applied for some years before to coast, and ran ashore on the same night near Dunthe Tour de Cordouan. The light is revolving, bar. The Tour de Cordouan has, in our times, appearing in its brightest state
every been made illustrious by the first application of the minute. Elevated 150 feet above the sea, it is dioptric contrivances of Fresnel, which Alan Stewell seen as far as the curvature of the earth per- venson has borrowed, not without ample acknowlmits, and even at more than twice the distance at edgment, nor without some improvements, for the which the curvature would interfere were the eye service of his own country. of the observer on a level with the sea ; for it is Mr. Stevenson, while treading in the footsteps seen as a strong light from the high land of the of Smeaton and his father as historians of their Isle of Barra, thirty-eight iniles distant.
great works, has largely availed himself of the In a chapter which Mr. Stevenson devotes to progress which has taken place in the art of enthe general history of lighthouses, he has col-graving. It is amusing in Smeaton's folio to oblected the few and meagre notices which remain serve the costume of days when the rough busito us of those constructed by the nations of ness of life was transacted under wigs and in antiquity. We can hardly doubt that some must shorts and shoebuckles; but the lapse of time is have existed of which no record has been pre- no less apparent in the delicacy and beauty of the modern illustrations. On no part of his work has tain number of Argand lamps are disposed on a Mr. Stevenson been more lavish of this useful and frame-work, each in front of a metallic reflector, instructive adjunct to a pregnant text than in the which latter is always moulded to a parabolic treatise which he devotes to the curious subject of curve. Both in this and the dioptric system the the illumination of lighthouses. No such assis- first great division adopted for the important purtance, indeed, can bring a disquisition so pro- pose of distinction and identification is into fixed found and such an array of mathematical science and revolving lights. The catoptric system, by within the grasp of the unlearned.
the aid of various contrivances, has been made however, but an uninstructed glance at these susceptible in practice of nine conspicuous and unpages to show that when the engineer rests from mistakeable varieties; for which differences of his architectural labors he has further difficulties color, periodical gradations of splendor, and absoto encounter and problems to solve, which require lute temporary occulation are the means employed. an extraordinary combination of theoretical science The relative arrangement of the lamps with their and practical skill. The Promethean task remains reflectors to each other differs according as the to which the construction of the corporeal frame light is fixed or revolving. In the fixed light the is but subsidiary. It may at first appear a simple lamps and reflectors are disposed on a circular matter to accumulate within a limited space in- frame with the axes of the latter inclined to each struments and materials of luminous combustion, other at such an angle as shall enable them to and to trust to the unassisted laws of radiation for illuminate as completely as possible every quarter the diffusion of the light produced. The result, of the horizon. The• revolving light is produced however, of this process would be to direct an im- by the revolution on a central shaft of a frame mense proportion of the rays in sheer waste to with three or four sides, on each of which the wards the zenith or the centre of the earth. It be- reflectors are disposed with their axes parallel. comes the business of the engineer, no longer an One variety, indeed, the flashing light, is produced architect but an optician, to control the rays and by a somewhat different arrangement, involving to direct their divergence on the system best suited an inclination of the axis of each reflector to the to the local conditions of the edifice, to adapt the perpendicular. In the dioptric system a powerful range of visibility to the circumstances of the navi- burner is placed in the centre of a frame, usually gation, and to give a specific character to the octagonal, fitted with a refracting lens to each flame which shall enable the mariner, without hes of the sides. itation or mistake, to distinguish it from others. Contrivances of great ingenuity and complexity It is laid down by Mr. A. Stevenson that no two have been superadded by Messrs. Fresnel and lights similar enough to be confounded should be Stevenson both for reflection and refraction of placed on the same line of coast nearer than one much of the light, which, without their aid, hundred miles to each other.
would be wasted in an upward or downward diThe various inventions which have been, with rection, entitling the whole apparatus, combining, a view to these various objects, substituted for the as it then does, the qualities of the two systems, candles of Smeaton and the brazier of the Isle of to the designation of catadioptric. We are sorry May are of recent date. Many of them were, to confess that, in spite of the removal of those as is usual, preceded by those vague suggestions vexatious excise regulations which so long paralwhich often put in a claim for original invention, yzed the glass manufacture of England, we are but scarcely diminish the honor of successful ac- still dependent on France for the glass used in the complishment. Among the names of those who construction of our dioptric lights. Mr. Stevenhave contributed most effectually to the present son has entered fully into the subject of the comefficiency of the system of marine illumination, parative merits of the two systems. For lights of Argand, Borda, and Fresnel are conspicuous. the first order in range and importance, specified The hollow cylindrical wick of the first was a by him—as those which are first made on oversudden and immense advance in the art of econom- sea voyages—and which embrace within their ical and effective illumination. The second ap- action a large portion of the horizon—it seems plied the parabolic mirror to the light of Cordou- clear that the dioptric system is to be preferred. an--an invention which has multiplied the effect In respect of intensity, equable diffusion of light of the unassisted flame in the case of a fixed light in the direction required, and economy of oil, it by 350, in that of a revolving light by 450. For has decidedly the advantage—in the latter parthe merits of that great master of the more com- ticular in the proportion of three and a half to one. plicated system of the refracting lens, termed the The consequence, however, of extinction from acdioptric, Fresnel, we must refer our readers to cident is, as Mr. Stevenson terms it, infinitely Mr. Stevenson's pages and their elaborate en- great in the case of the one central burner of the graved illustrations. It may, however, for the dioptric system as compared with that of the nubenefit of that portion of our readers whose com- merous lamps of the catoptric. There are also prehension of optical contrivances cannot be as- cases, such as those of fixed lights in narrow seas, sisted by the use of Greek terminology, be per- where it is only needful to illuminate a limited mitted to us to state here in few words some of segment of the horizon, in which he prefers the the leading and distinctive features of these two reflected light. He condemns the employment systems of illumination. In the catoptric, a cer- of colored media on the score of absorption, and considers it only admissible in the case of a line and economy may be fairly consulted. Our chilof coast crowded with lighthouses in which the dren, perhaps we ourselves, who remember the other and better processes of revolution and tem- old lamps and older watchmen of London, may porary occulation have been exhausted. In such live to read gas-shares at a discount, and to see the red glass may be used, but blue and green, the nocturnal duty of the policeman simplified by from their greater absorption, are not entitled to the radiance of artificial suns which shall fill whole promotion from the shop of the apothecary. regions of streets and alleys with light from one
The critical position and permanent require central source. ments of the lighthouse make it improbable that Apart from such extended speculations, we conthe oil-lamp will soon be supplanted on the sea- sider it not unlikely that the experiments pursued girt tower either by gas or by any of those still and the processes adopted for marine illumination more recondite devices which are almost daily may suggest minor improvements which, though engendered by the advancing chemical science of of less importance, may conduce to public and the age. Gas, indeed, has sometimes been ap- private convenience. The house of lords, clubplied to marine-lights on the mainland. For the rooms, and other large enclosed spaces, have been dioptric-light, where there is one large central assisted by Mr. Faraday and others by various flame, it possesses, at least, two decided advan- methods to get rid of unhealthy gases and supertages—the form of the luminous cone is less fluous caloric. The great saloon of Lansdowne variable, and the inconvenience of mechanism in | House has, if we mistake not, long been partially the lamp is avoided. These advantages are, how- lighted on festive occasions from without ; and ever, more than compensated in all positions to Lord Brougham, we hear, has lately availed himwhich access is difficult and precarious, by the self of a similar resource in the old hall of his difficulties of the manufacture of the gas and seat in Westmoreland, without at all disturbingtransport and storing of fuel; perhaps in all cases on the contrary, aiding and enhancing-its imby the risk, however reduced by modern inven- pressive character. We are not aware that any tions, of explosion. For the catoptric revolving- attempt has yet been made towards the effective light it is obviously unsuited.
illumination of a large room without any interior To the Drummond and Voltaic lights there are combustion. We understand, however, that Mr. other objections than those which adhere to any Barry has such an attempt in contemplation for process involving delicacy of adjustment and ma- the picture-gallery at Bridgewater House, and nipulation. A full exposition of those objections this by the aid of the parabolic reflector of the would require some of that mathematical disquisi- Cordouan and the Bell Rock. Guttering-candles tion and graphic illustration which Mr. Stevenson and broiling-lamps are behind the age we live in, has lavished in his pages for the use of the learned. and we have every reason to wish Mr. Barry sucIt is sufficient here to explain that, to fulfil the cess. purpose of a marine light, whether fixed or re- We cannot attempt the delicate task of a biogravolving, some degrees of divergence are essential phy of living worthies. The peculiar line in which -that to produce this divergence, and to control the two Messrs. Stevenson have attained eminence and direct it either by the mirror or the lens, a sufficiently distinguishes them from that family of body of flame, as distinguished from a luminous English engineers who have made illustrious a name point, is equally necessary. Such operators as so nearly similar, that confusion between them and the Fresnels and Stevensons leave nothing to their respective achievements might otherwise poschance to any chance, at least, but that of fog sibly arise. It is a satisfaction to us, however, to or violent accident. That effect, whether of slow- relate, that the architect of the Bell Rock, having ly-increasing and waning splendor, or of fixed retired from the office of engineer to the Northern radiance, which at the distance of twenty miles Lights, is still enjoying an honorable repose in Edcheers the spirit and directs the judgment of the inburgh, and that his son and successor in office is mariner, is previously calculated and rigorously at present superintending the building of five lightgoverned by so small a quantity as the measured houses in Scotland. diameter of the cylindrical wick placed in front For the last century England has been a great of the mirror or behind the lens. If this diame- school for the practical application of mechanical ter, as in the case of the Drummond and Voltaic science. It is somewhat curious to compare the processes, be reduced to a luminous point, of how- present condition of her intellectual resources in this ever concentrated and increased intensity, practical department with those of the earlier attempts to utility is annihilated. An experiment was made light the Eddystone-the proceedings and results by Mr. Gurney in 1835 for adding power to the of solid instruction with the desultory efforts of amflame of oil without reducing its dimensions by a ateur ingenuity. A country gentleman and a silkcombination with oxygen, but the plan was reject- mercer were the predecessors of Smeaton at the ed by the Trinity House.
Eddystone. The first, Mr. Winstanley, had disSuch, however, is the intensity of the light tinguished himself by a talent for practical mechanproduced by some of these processes, that we can- ical jokes, which must have made his country house not despair of their ultimate application to pur- in Essex an agreeable and exciting residence for poses and situations which afford a safer field for an uninitiated guest. You placed your foot in a ingenuity, where accident is of less consequence slipper in your bed-room, and a ghost started up