Extracts from William Hutchinson’s Treatise on Practical Seamanship, 1791 (3rd Edition)

 

A

TREATISE

FOUNDED UPON

Philosophical and Rational PRINCIPLES,

TOWARDS ESTABLISHING FIXED RULES,

For the best FORM and

Proportional Dimensions in Length, Breadth and Depth of

Merchant’s Ships in General ; and also the MANAGEMENT

of them to the greatest advantage,

BY

Practical Seamanship ;

WITH

IMPORTANT HINTS AND REMARKS

RELATING THERETO

FROM

LONG APPROVED EXPERIENCE.

BY WILLIAM HUTCHINSON, MARINER

And DOCK MASTER at LIVERPOOL

LIVERPOOL

PRINTED BY THOMAS BILLINGE, CASTLE-STREET.

M,DCC,LXXXXI

Plate 10

On LAND-MARKS And LIGHT-HOUSES.

THOSE that are for leading marks to avoid dangers, and to be erected near the sea shore for this important purpose only, should be made to differ as much as possible in appearance from other common buildings. And if there are Charts of the place, their likeness should not only be laid down in minature, in their real situations, with compass lines of direction leading to them ; but also in large figures, with their heights in feet, in vacant parts of the Charts; that strangers may know them, and their intended purpose the better ; as is done in our Charts of Liverpool ; and where the fronts of the land-marks, towards the channels, are painted black, read and white, in large divisions, that they may be the more surely distinguished in the different states of the atmosphere and weather.

On LIGHT-HOUSES In GENERAL.

AS many valuable lives, and great property, often depend upon the certainty of seeing these lights, at a sufficient and proper distance, no pains or expence should be spared to make them as perfect as possible, to answer their designed purpose ; especially where there is a sufficient fund allowed to support them ; or where the increase of trade or shipping make large profits arise from them. It well deserves the attention of the public, to get our light-houses improved upon the best plan, for the greater safety to shipping, and consequent advantages to all concerned therein.

It is well known, from reason as well as experience, that an open coal fire light, exposed to all winds and weathers, cannot be made to burn and show a constant steady blaze to be seen at a sufficient distance with any certainty ; for in storms of wind, when lights are most wanted, these open fires are made to burn furiously, and very soon away, so as to melt the very iron work about the grate ; and in cold weather, when it snows, hails, or rains hard, the keepers of the lights, not caring to expose themselves to the bad weather, are apt to neglect the fire till it is too low, and then throw on a large quantity of coals at once, which darkens the light for a time, and till the fire burns up again; and in some weathers it must be difficult to make them burn with any brightness. And when they are inclosed in a glazed close light-house, they are apt to smoke the windows greatly, nor do they afford so constant a blaze as oil lamps, with reflectors behind them, which we have adopted at Liverpool.

On Light-houses, with Oil Lamps, and Reflectors.

IT is well known from experience that our common street lamps, when the oil is good, will burn a long winter’s night of sixteen hours, without any attendance, and consume but very little wick ; which plainly proves them the most certain, constant, steady and uniform lights, that can be used in light-houses, to direct shipping in their passage through dangerous and narrow channels, as at Liverpool ; which being situated in a deep, dangerous bay, with shoal sand banks at a great distance from the shore (as may be seen by the Chart) lies open and exposed to the most current storms of westerly winds, and to strong tides, which raise high and dangerous waves ; and which occasioned many great and fatal losses before the year 1763; at which time four light-houses were erected; two large ones, called the sea lights, leading through the channel out to, and in from sea, till the two lesser Hoylake lights are brought in a line that leads into a very good road-stead to lie in, till it is a proper time and tide to proceed to Liverpool as may be seen by the Chart. The losses have been very few in comparison to what they were before these light-houses were built ; which prove their great use to the trade of this place for safety as well as expedition, in getting out and in by them. They are built from twenty five to one hundred and one feet high, as the situations and necessity required ; two of them being a great height above the level of the sea, as the curvature of our globe requires, according to the rules laid down in several of our navigation books, which should always be in proportion to the distance of the shoals from the light-houses, which should be so high as to appear and be seen above the horizon from a ship’s deck at a sufficient distance without the shoals, so that her situation may be known by the lights being open or nearly in a line, either to run in, or to get and keep the ship off by them in a fair way, as the occasion of time, and tide may require.

These lamps, and reflectors, as represented in plate 10, fig. 1 and 2, are fixed in the light-room, right fronting the channel, or line of direction for a fair way, and opposite the middle of the window, which is high enough in proportion to the reflector, and extends in width, each way, as far as the light can, or may require to be seen.

These reflectors are made, as near as can be, to the parabolic curve ; thus: draw a set of parallel lines right across the focus or center line; mark the focal distance above the parallel lines, and take an extent from the focal distance, to each parallel line, one after the other; with these extents, mark each parallel line in its turn, from the focus or burning point, with dots on each side of the focus line, to the extent of the designed diameter, and make a regular sweep from dot to dot, as represented in plate 10, fig. 3 ; by which method a form may be made, for the curve of a parabolic reflector of any focus or diameter, to have the property, when the sun’s, or any other ray of light or fire come upon them in parallel lines they are reflected to, and cross each other at the focus; which makes the focus the burning point; and just the contrary effect takes place, when a burning blaze of fire or light is fixed in their focus, all the rays of light that fall upon them are reflected right forward in parallel lines, with more or less power in proportion to the lustre or brightness of the reflectors, which are illuminated so as to look like a blaze as big as the reflectors themselves, to people in that quarter nearly facing their axes, by the angle of reflection being equal to the angle of incidence.

We have made, and in use here, at Liverpool, reflectors of one, two, and three feet focus ; and three, five and a half, seven and a half, and twelve feet diameter ; the three smallest being made of tin plates, soldered together ; and the largest of wood, covered with plates of looking glass, shaped as represented by fig. 1 and 2, plate 10, and fixed as near as can be to the abovementioned rules: the lamp or cistern part is of copper, for the oil and wick behind the reflector, so that nothing stands before the reflector, to intercept the blaze from acting upon it, but the tube that goes through it, with a spreading burning mouth-piece, to spread the blaze of the lamp parallel to the middle of it, just in the focus or burning point of the reflector, as may be seen by the figures abovementioned.

We have a feeding-can, with oil, to stand upon the cistern of each lamp, to supply the consumption of oil, and to keep it near to the level of the mouth of the lamp, near which is a little rim, to prevent any drains of oil along the tube to the reflector (as may be seen in fig. 2,) which drops from the rim into a dripping pan that stands below the reflector ; and if the cock of the feeding-can be turned to run too fast, to prevent an overflow of oil, there is a small hole, and a tube in the cistern, that lets the oil into a tin can standing below it. The lamps, like the reflectors, are proportional in their bigness, to make a greater or less blaze, as the distance, at which they are to be seen, requires ; their spreading burning parts are from three to twelve, and fourteen inches; which makes the blaze the same breadth, and burns higher or lower, according to the quality of the oil, on which the goodness of the lights greatly depends. The wick is common cotton thread, spun for the purpose of lamps, and wound in lengths to fill the mouth of the lamps about a quarter of an inch thick ; and, as it consumes, there are long mouth-pincers, adapted to the lengths of the wicks, to haul out the wicks through the tubes, as the occasion requires: they are snuffed with a pair of sheers in one hand, whilst a tin box is held, with a little water in it, in the other, to receive the snuffings, and prevent the danger of fire ; and they require to be attended and trimmed by their keepers, every three hours.

These light-houses, constructed, kept, and situated as abovementioned, have stood the test of a fair trial ; and great preference and advantages have been allowed them, even by their opposers ; for such there always will be to new things; commonly calling them new whims ; till time and trial confirm them useful improvements ; which these are confessed to be by all that have seen them; for in a dark clear night, the two sea lights (notwithstanding their height, and the curvature or roundness of the sea, as before mentioned, may be plainly seen when they are in a line with the horizon, not only from the deck, but from the mast head of a ship, which gives the advantage to see which way they are open, to bring them in a line in good time, either to keep the ship off, or to run by them in a fair way, as the circumstances of the time and tide, prudently considered, may require.

But it may be said, that these reflecting lights only suit such places as require them to be seen only from one quarter of the compass ; which must be acknowledged, though two of our lamps give a blaze twelve and fourteen inches square, and there is but little reflected light above three points of the compass each way ; but then, it must be allowed, that the blaze of the lamps can be seen as in common with other lights, above half the compass, clear of the edge of the reflectors, which will illuminate the atmosphere fronting them, so as to add greatly to the light, even in that situation.

A Light-house that may require to be seen above one half, or 3-4ths of the compass, may be fixed, upon this plan, with two or three reflectors ; one to face each quarter ; and to have the tubes seen for the lamps from one cistern ; or to serve a parcel of small lamps, with reflectors of four inch focus, and eleven inch diameter ; as represented in plate 10, fig. 4, 5: which may be set upon shelves in rows very near the window ; the upper row nearest ; and those below, a little behind, to prevent those below from smoking those reflectors, above them : by such means the rays of light that would go towards the land or against a dead wall, where they are not wanted, are reflected forward to add to the light that goes towards the shipping, for which they are designed.

But where a light-house requires to be seen equally from all quarters quite round the compass, and lighted with a number of candles, or common lamps; (as it is known from experience, that rays of light pass and cross each other freely in all directions, without any visible interruption; (it becomes a disputed point, whether reflectors, would be of any service. In my opinion a number of those hand lamps, with reflectors set round, upon shelves near the windows, as abovementioned, would reflect many, rays of light in a horizontal direction, clear of the smoke, that would fall above and below the windows, and throw more light, through the windows, with, than without the reflectors, from an equal quantity of lights ; but the advantage that would be gained, wants to be confirmed by experiment.*

These hand lamps and reflectors were contrived to make night signals by lights, to be set in the staircase windows of our upper sea-light-house, that fronts towards the town, in case of any vessel being perceived in distress in the night, or when it is too dark to see the day signals, which are represented with the lighthouse, fig. 6, plate 10, as they are printed upon cards to make them known ; and as they have given general satisfaction since they have been in use, and afford information of a greater number and variety of different vessels than any other set of signals I have seen, I thought they deserved this notice. Besides these public signals, several merchants have flag staffs erected at a little distance from the light house ; so that when their ships appear with their own particular signals, their colours are hoisted on their flag staffs, for their information.

The situation of this light-house is well adapted to answer all these purposes, from standing fronting the town and docks, at three miles distance, upon a hill about 40 yards high above the level of the sea at high water; which makes it very conspicuous both from the town and at sea ; it being the first object that appears on shore above the horizon, in a fair direction for this channel, as may be seen by the chart.

But to return to the hand-lamps and reflectors, as beforementioned. I tried one of them with our reflectors of three feet diameter, and one foot focus made and glassed as represented in fig, 1, 2, but it proved greatly inferior, though it might be seen at nine or ten miles distance; and on trying them with a common shop lamp, with equal wicks, and set in different windows of the stair-case of the light-house that faces the town as abovementioned, I found the reflected lamp eclipsed the common lamp to such a degree that I could see it, without using a spy-glass, at three miles distance. These small reflectors were only beat out of common tin ; but if they were improved and made of blown quick silvered glass, silver plated copper, or reflecting telescope metal, as concave mirrors, and soldered all together with the lamp in a tin pan like a dripping-pan, (as represented in fig. 4 and 5) only with the addition of tin stays behind, the reflectors, to keep all together in handing them about ; it is a doubt with me, whether a number, set as abovementioned, would, not be preferable to our large reflectors ; for I have perceived from experience, that our large reflectors of one foot focus, and three feet diameter, reflect a stronger light, in proportion, than our large reflector of twelve feet diameter and three feet focus. For the quantity of light received upon any given surface, will decrease in the same proportion as the square root of the distance from the luminous body is increased, four, eight, and sixteen times less, &c. Therefore from all my experience and observations, I would recommend small reflectors of 11 inches diameter and 4 inch focus, made with what is now called Mudge’s reflecting telescope metal, as published in the Philisophical Transactions, December 1777 ; by which I got one made and compared with one of the size and focus, in a nice manner, glassed with six sided quick silver glass, which the metal one greatly surpassed in fair trials. And these two small reflectors have been in use for some time, at a house built on the Point of Linas, on the island of Anglesea, for our Liverpool Pilot’s station, who give a good report of it.

Another great benefit I thought might rise from these hand reflectors if they were brought to perfection ; which was, that single light-houses might be distinguished one from another, by having different numbers of windows illuminated by them ; but in trying experiments with two of them, set in the first and second staircase windows of the light-house already mentioned, fig. 6, they appeared, at three miles distance, only as one light, though they were above ten feet asunder ; and they required to be set in the first and third windows, which are above nineteen feet asunder, to appear as two distinct lights, at three miles distance : which shews how much these imperfect hand reflectors illuminated the atmosphere, and how necessary are experiments before new designs of this kind are put in execution.

In light-houses, where reflectors are designed to be used, and the lights required to be seen at the greatest distance possible, according to their high and low situation above the level of the sea, the reflectors should be made to stand with their axes, or centers, pointing to the horizon ; but where they are only required to be seen at a small distance to lead over a bar, or through a channel near them, then the reflectors should be pointed to the most necessary or most dangerous place ; by which means the most rays of light are reflected to where they are most wanted. And from experience we find, that plate ground glass answers much the best, both for reflectors, and the light-room windows : and the larger panes, and the less wood in the window frames to obstruct the light, the better ; and the windows that are framed round or made circular, as well as the light-houses, stand and resist the wind much better than those that are made flat by the octagon or eight sided form. And to keep light-rooms as clear of smoke as possible, I would recommend a large opening in the centre of the conical roof, with a nice cover, and a large vane to make it traverse freely with the wind; the spindle to be fixed to what is called the dragon, with its point through a collar into a socket below it : for to withhold whatever contrivance, or the best materials that can make them most perfect, as far as their fund which is to support them will afford, should be looked upon as an act of great villainy, for the reasons given.

Experience makes another remark here necessary ; that without there is a small vacuity made in the walls of light-houses, for the wet to drain down, it will beat through, and rot the wood work.

On Improved LAMPS for REFLECTORS.

IT is a plain and obvious fact with respect to reflected light, that, the strength of it must necessarily be, in an exact proportion to the brightness and intensity of the luminous body. Since the introduction therefore of what is called the Patent Lamp (which must be allowed greatly to exceed all others in this important point) it is very natural to expect, that the utility of our present lights, which have hitherto had very happy effects, may be rendered much more complete, by applying a burner upon the same principle as the Patent Lamp, before the reflector, in lieu of that made use of at present. With this view, several experiments have already been tried, with a metal reflector of eighteen inches diameter; and those, have suggested other experiments, which hold out still more extensive improvements. We tried the effect of small lenses with small reflectors, which proved the advantage of the principle, but could not get large lenses of solid glass made here, but got some blown in the form of a plano convex, like a bottle, and filled with strong brine to prevent their being broke by frost, which answered the purpose to magnify the light, but the heat of the blaze of the lamp and reflector broke them.

Mr. ROGER’s Improvements for Light-houses.

On Improved Glass Reflectors and Lamps, with Solid Glass Lenses before them for Light-Houses.

These improvements were brought to Liverpool by Mr. Thomas Rogers, whose address was Patentee for “stained reflectors, &c.” in London, related the history of his proceedings to the author as follows.

The Trinity house in London, very generously built a temporary light-house on Black Heath, to try experiments to improve light-houses, and after they had done very laudably, advertised liberty to any other people to try experiments for this important purpose.

Mr. Rogers being in the glass trade as abovementioned, got reflectors blown in one piece of glass to their form, and by a new method silvered over the convex flue without quick-silver, made them very bright good reflectors, and had what I call a large circular patent lamp three inches diameter, consequently the wick nine inches round, stands at the focus of the reflector, and before it a plain convex lens of solid glass twenty one inches diameter and five inches and a half thick in the focus, which makes the light answer the principle of the Magic lantern upon an enlarged scale.

The first of this improvement was ordered and put in use at one of the Portland light-houses, next at the Hill of Hoath near Dublin, the report of them seems incredible, and to very great advantage in hazy and foggy weather. And he is now putting them up at Waterford light-house, and brought one of them here to Liverpool, and had it tried in three different places to compare with reflectors made with plain pieces of looking glass which it surpassed.

In the last conversation I had with him, his reflectors were but twelve inches diameter, he said he would get them enlarged to eighteen inches, then he reckoned he would not lose one ray of light from going through his lenses, which I hope will have a fair trial at our light-houses here, where we require the most perfect fights that can possibly be got made, not only to be seen at the greatest possible distance without our most extensive sand banks, to let ships see that they are in a fair way, but to diverge to each side as much as necessary, to let them see when they are out of a fair way, which is the most important, for ships in a fair way, are in no danger in comparison with those that are out of a fair way, as may be seen by the charts of our Harbour.

 

 


* There has lately been a Light-house erected upon the small rocks at the South entrance of St. George’s channel, designed to be seen all round the compass ; with the oil cistern in the center, that supplies four reflectors of 5 and a half feet diameter as represented figure 1, plate the 10th, and has the report of being a good Light-house and being seen all round, though the reflectors only front the four quarters.

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