1846. 



fHE CIVIL ENGINEER AND ARCHITEcrS JOURNAL. 



2n7 



the lights was thus greatly increased, hut the introduction of a revolving 

 frame proved a valuable source of differences in the appearance of hghts, 

 and, in this way, has since been the means of greatly extending their utility. 

 The exact date of the change on the light of the Corduan is not known ; but 

 as it vras made by Lenoir, the same young artist to whom Borda, about the 

 year 1780, entrusted the construction of his reflecting circle, it has been 

 conjectured by some that the improvement of the light was made about the 

 same time. The reflectors were formed of sheet-copper, plated with silver, 

 and had a double ordinate of 31 French inches. It was not long before 

 these improvements were adopted in England, by the Trinity House of 

 London, who sent a deputation to France to inquire into tlieir nature. In 

 Scotland, one of the first acts of the Northern Lights Board in 1786, was to 

 substitute reflectors in the room of the coal-light then in use at the Isle of 

 May in the Frith of Forth, which, along with the light on the Cambrae Isle 

 in the Frith of Clyde, had, till that period, been the only beacons on the 

 Scotch coast. The first reflectors employed in Scotland were formed of 

 facet! of mirror-glass, placed in hollow paraholoidal moulds of plaster, 

 according to the designs of the late Mr. Thomas Smith, the Engineer of the 

 Board, who (as appears from the article Reflector, in the Supplement to the 

 third edition of the ' Enclyclopzedia Britannica') was not aware of what had 

 been done in France, and had himself conceived the idea of this combination. 

 The same system was also adopted in Ireland ; and in time, variously modi- 

 fied, it became general wherever lighthouses are known," 



The reflectors used in the best lighthouses are made, says the 

 writer, 



" Of iheet-coppcr plated in the proportion of six ounces of silver to 

 sixteen ounces of copper. They are moulded to the paraholoidal form, by a 

 delicate and laborious process of beating with mallets and hammers of various 

 forms and materials, and are frequently tested during the operation by the 

 application of a mould carefully formed. After being brought to the curve, 

 they are stiffened round the edge by means of a strong hizzle, and a strap of 

 brass which is attached to it for the purpose of preventing an accidental 

 alteration of the figure of the reflector. Polishing powders are then applied, 

 and the instrument receives its last finish." 



" The flame generally used in reflectors, is from an Argand fountain. lamp, 

 ■whose wick is an inch in diameter. Much care is bestowed upon the manu- 

 facture of the lamps for the Northern lighthouses, which sometimes have 

 their burners tipped with silver to prevent wasting by the great heat which 

 ia evolved. The burners are also fitted with a sliding apparatus, accurately 

 formed, by which they may be removed from the interior of the mirror at 

 the time of cleaning them, and returned exactly to the same place, and 

 ] ocked by means of a key. Tbia arrangement, as shown in figs. 1 and 2, 



Pig. 2. 



Pig. 1. 



is very important, as it insures the bnrner always being in the focns, and 

 does not require that the reflector be lifted out of its place every time it is 

 cleaned ; so that, when once carefully set and screwed down to the frame, it 

 is never altered." 



It will please our readers very much to find in Mr. Stevenson's 

 book, the many clever tools which are used, and care which is 

 taken to make the lamps and lights as good as may be. He has 

 written a good deal about feeding the lamps with oil, and indeed 

 everywhere he has sliown that he is master of his work, even in 

 the smallest things. It was said of the Duke of Wellington, that 

 even to the horses' shoes he knew everything in his army, and that 

 he thought nothing beneath him which had to do with the welfare 

 of his men : and so should it be with the engineer ; and this is the 

 way in which he can truly become a working-man. Mr. Stevenson 

 may not perhaps have put on a fustian coat, nor spent his time in 



filing, rasping, and fitting; but an engineer may be a working-man 

 without that. 



Lights are found by seamen so useful, that they are always 

 calling out for more ; but when put up, it becomes very trouble- 

 some to know one from another. A light ought to make' known to 

 the benighted mariner the land he has made, as the sight of a hill 

 or tower would have shown him in the day ; therefore, it becomes 

 needful that each should be readily known, so as not to be 

 mistaken. 



" Catoptric lights are susceptible of nine separate distinctions, which are 

 called /xerf, revolving white, revolving red and ichife, revolving red wil/t two 

 whiles, revolving white with two reds, flashing, intermittent, donble fired 

 lights, and double revolving white lights. The first exhibits a steady and 

 uniform appearance, which is not subject to any change ; and the reflectors 

 used for it (as already noticed) are of smaller dimensions than those emploved 

 in revolving lights. This is necessary in order to permit them to be ranged 

 round the circular frame, with their axes inclined at such an angle, as shall 

 enable them to illuminate every point of the horizon. The revolving light 

 is produced by the revolution of a frame with three or four sides, having 

 reflectors of a larger size grouped on each side, with their axes parallel ; 

 and as the revolution exhibits once in two minutes, or once in a minute, as 

 may be required, a light gradually increasing to full strength, and in the 

 same gradual manner decreasing to total darkness, its appearance is extremely 

 well marked. The succession of red and white lights is caused by the revo- 

 lution of a frame whose difl'erent sides present red and white lights ; and 

 these, as already mentioned, afford three separate distinctions, namely, alter- 

 nate red and white ; the succession of two white lights after one red, and 

 the succession of two red lights after one white light. The flashing light is 

 produced in the same manner as the revolving light ; but owing to a dirterent 

 construction of the frame, the reflectors on each of eight sides are arranged 

 with their rims or faces in one vertical plane, and their axes in a line inclined 

 to the perpendicular, a disposition of the mirrors which, together with the 

 greater quickness of the revolution, which shows a flash once in five seconds 

 of time, produces a very striking eflfect, totally diflferent from that of a 

 revolving light, and presenting the appearance of the flash alternately rising 

 and sinking. The brightest and darkest periods being but momentary, this 

 light is farther characterised by a rapid succession of bright flashes, from 

 which it gets its name. The intermittent light is distinguished by bursting 

 suddenly into view and continuing steady for a short time, after which it is 

 suddenly eclipsed for half a minute. Its striking appearance is produced by 

 the perpendicular motion of circular shades in front of the reflectors, by 

 which the light is alternately hid and displayed. This distinction, as well 

 as that called the flashing tight, is peculiar to the Scotch coast, having been 

 first introduced by the late Engineer of the Northern Lights Board. The 

 double liKhts (which are seldom used except where there is a necessity for a 

 leading line, as a guide for taking some channel or avoiding some danger) 

 are generally exhibited from two toners, one of which is higher than the 

 other. At the Calf of Man, a striking variety has been introduced into tb« 

 character of leading lights, by substituting, for two fixed lights, two lights 

 which revolve in the same periods, and exhibit their flashes at the same 

 instant ; and these lights are, of course, susceptible of the other variety 

 enumerated above, that of two revolving red and white lights, or flashing 

 lights, coming into view at equal intervals of time. The utility of all these 

 distinctions is to be valued with reference to their property of at once 

 striking the eye of an observer, and being instantaneously obvious to 

 strangers." 



Although colour is needful, it is in itself a very great evil, for 

 the coloured screens stop much of the light. Several colours have 

 been tried, but red, blue, and green have alone been found useful ; 

 and the two latter only at such short lengths, that they are alto- 

 gether unfit for sea-lights. Even the red lights take up from four- 

 sevenths to five-sixths of the whole light, wliicli is a very great 

 loss ; and the deeper the red, the greater the loss of light, — while 

 the less red there is, the less can it be seen by the seaman. Red 

 lights ought, therefore, to be used as little as may be. In Scotland, 

 instead of a red screen or disc, a chimney of red glass is used. 



We now come to the use of lenses, upon which the writer says : — 



" One of the earliest notices of the application of lenses to lighthouses is 

 that recorded by Smeaton in his ' Narrative of the Eddystone Lighthouse,' 

 where he mentions a London optician, who, in 1759, proposed grinding the 

 glass of the lantern to a radius of seven feet six inches ; but the description 

 is too vague to admit of even a conjecture regarding the proposed arrange- 

 ment of the apparatus. About the middle of the last century, however, 

 lenses were actually tried in several lighthouses in the south of England, and 

 in particular at the South Foreland in the year 1752; but their imperfect 

 figure and the quantity of light absorbed by the glass, which was of impure 

 quality and of considerable thickness, rendered their efl'ect so much inferior 

 to that of the parabolic reflectors then in use, that after trying some strange 

 combinations of lenses and reflectors, the former were finally abandoned. 

 Lenses were also tried at the lights of Portland, Hill of Howth, and Water- 

 ford, by Mr. Thomas Rogers, a glass manufacturer in London ; who possessed, 

 it is said, the art of blowing mirrors of glass, ' and by a new method silvered 

 over the convex side without quicksilver.' 

 " The merit of having first suggested the building of lenses in separate 



