Smeaton and Lighthouses Part 7

The Dutch were the first to adopt Fresnel's system. In the year 1834 the Commissioners of Northern Lighthouses sent Mr. Alan Stevenson to Paris to inspect the system, and his report was so favourable, that the reflecting apparatus of the revolving light at Inchkeith was removed, and the dioptric instruments subst.i.tuted. The new light was exhibited on the evening of the 1st of October, 1835, and so great was the satisfaction afforded, that a similar change was made at the fixed light of the Isle of May. The Trinity-House of London followed next in adopting the improved system, and a revolving dioptric light of the first order was erected at the Star Point in Devons.h.i.+re.

In the lighthouses of this country sperm-oil is the most usual fuel.

In France[6] an oil is burned called Colza oil, expressed from the seeds of a species of wild cabbage. In the lighthouses on the Mediterranean olive-oil is used. In a few lighthouses near large towns coal-gas has been advantageously adopted. Much also has been said in favour of the Drummond and Voltaic lights, which, on account of their prodigious intensity would appear to be most desirable; but the uncertainty which attends their exhibition renders it at present impossible to adopt them: but there is a yet more fatal objection--the smallness of the flame renders them wholly inapplicable to dioptric instruments, which require a great body of flame in order to produce a degree of divergency sufficient to render the duration of the flash in revolving lights long enough to answer the purpose of the mariner.

In the year 1835, Mr. Gurney proposed a lamp of great power in which the flame of oil or wax was sustained by streams of oxygen gas, a method said to be more economical than the combustion of oil in atmospheric air. The Trinity House entertained the proposal, and inst.i.tuted a number of experiments. In applying this light to reflectors it is intended to use three small flames, each about three-eighths of an inch in diameter, productive, it is said, of an effect equal to that of ten Argand lamps. But for lenses the burner has seventeen films of flame, and is said to possess six times the power of the Fresnel lamp.

In the year 1840, Captain Basil Hall inst.i.tuted a series of experiments to ascertain whether the well-known superior brilliancy of a revolving light could not be obtained for a fixed or continuous light, that is, for one equally visible in all directions at the same moment. His idea was, that by giving a certain velocity of revolution to a series of lenses round a fixed light, as in Fresnel's arrangement, a continuity of illuminative power, equal almost in brilliancy to that of a slowly revolving light, might be produced. The apparatus was arranged so as to cause a series of eight lenses one foot in diameter and three feet focal distance to revolve with any velocity up to sixty revolutions per minute round a central lamp. The light from this lamp being concentrated by refraction through the eight lenses into eight pencils, having a divergence of about eight degrees each, illuminated when at rest not quite fifty degrees of the horizon; but when this system of lenses was put into rapid motion, every degree of the three hundred and sixty degrees of the horizon became illuminated, so that to spectators placed all round the horizon the light would appear continuous and equally brilliant in every direction. The only question would be, whether or not this continuous light is essentially less intense than the light seen through the lenses at intervals when in slow motion; and this is a point which further inquiry must decide.

One of the causes which has tended to improve the brilliancy of lighthouses, has produced inconveniences, which long existed without remedy. During the combustion of a pound of oil, the union of its hydrogen with the oxygen of the air produces more than a pound of water in the state of vapour. When a cold wind is blowing upon the lantern of the lighthouse from without, this vapour is condensed into water upon the inner surface of the gla.s.s, and in very severe weather forms a crust of ice, in some cases, as much as four inches thick in the course of one night. This not only very much dims the brilliancy of the light to the sailor, but also entails a great amount of labour on the light-keepers, and injury to the lantern. The combustion of the oil also produces a large quant.i.ty of carbonic acid gas, which is of a very deleterious nature, and in many cases rendered the light-keepers'

rooms almost uninhabitable. Under these circ.u.mstances, the Trinity House made application to Dr. Faraday to investigate the subject, with a view to the discovery of some remedy. With his usual skill and sagacity, Dr. Faraday inst.i.tuted a number of inquiries and experiments, and visited some of the princ.i.p.al lighthouses. The result was the contrivance of a complete method of ventilating lighthouses.

On the dioptric system, the remedy was simple: it was merely to erect a tall chimney over the central lamp, and lead it out at the roof; by which means, the draught of the lamp was improved, and all the products of combustion carried off. On the catoptric system, with revolving lights, each lamp was furnished with a chimney, which pa.s.sed out at its upper extremity, through a small hole in the reflector into a fixed central hollow shaft, which served the purpose of a ventilating chimney to all the lamps. These plans are said to have been eminently successful in removing the inconveniences, which rendered the light less efficient, and the lighthouse an unwholesome and even dangerouse place of abode.

[Footnote 6: In the year 1836 the coast of France were provided with no less than ninety-six lighthouses.]

THE END.

Parker's Collections in Popular Literature.

Collections in Popular Literature, publis.h.i.+ng by John W. Parker, West Strand, London.

It has frequently been suggested to the Publisher, that he might render an acceptable service to the friends of Education, and greatly a.s.sist those who desire to promote the intellectual amus.e.m.e.nt of the people, by producing a series of Popular Books, at low prices, calculated, by their unexceptionable tendency, for general use in families; from which School Libraries might be formed, Reward Books selected, and Lending Libraries supplied; which, on account of their convenient form and size, would be welcome as Fireside and Travelling Companions; books, in short, which might be found instructive and entertaining wherever introduced.

These suggestions he is now carrying out, in compliance with certain conditions, namely, that the works produced shall be unexceptionable in subject and in treatment; that the series be sufficiently varied to meet the requirements of all cla.s.ses of readers; and that each book shall be complete in itself, and procurable for a very small sum.

The COLLECTIONS IN POPULAR LITERATURE will, therefore, embrace most of the features of an Encyclopaedia, though the subjects will not be divided into fragments, or scattered over many volumes; each subject being treated with fulness and completeness, and its information brought up to the present time.

The Plan will embrace new and improved Editions of certain Standard English books, but the majority of the works will be newly written, translated, compiled, or abridged, for the present purpose; and the volumes will appear from time to time in sufficient variety to extend simultaneously, and in due proportion, the various branches of Popular Literature. The whole will be prepared with an especial view to the diffusion of sound opinions--to the promulgation of valuable facts and correct principles--and to the due indulgence of general literary taste.

It is not intended that this series shall form a periodical, according to the strict acceptation of that term. Several works are already published, and others will quickly follow; they will all be uniformly bound in cloth and lettered. There will be no necessary connection between the various works, except as regards general appearance, and each, being complete in itself, may be had separately; nevertheless, the volumes, distinct, yet uniform in their object, will together form a valuable library, and may be collected and cla.s.sified under the following heads:

I. Popular History.

Under the comprehensive t.i.tle of History, we purpose giving an extensive series of interesting and instructive works. Among these will be carefully-considered narratives of some of those moral tempests which have so often agitated the world, when men have continued a long course of disobedience to the laws of G.o.d and the recognised laws of man. We shall make it our business to record the change of a dynasty, the rise and career of a monarch, a usurper, or a ruler, whose actions have thrown a new aspect on the political inst.i.tutions of a country; we shall trace the rise and progress of great commercial or manufacturing enterprises, whereby the wealth and prosperity of a nation have been obviously increased; we shall notice the train of events whereby the prevalent or established religion of a country has been changed. These and other subjects of a like character will enable us to bring up many stores from a mine peculiarly rich in instructive and entertaining matter.

It is of course impossible, in such a notice as this, to include all the features of so important a division of our COLLECTIONS IN POPULAR LITERATURE as History; but some idea may be formed of it from the following list of works which are nearly ready for publication:

A History of the Invasion of Russia by Napoleon Bonaparte; its Causes and Consequences. 2_s._ 6_d._

The Lord and his Va.s.sal: a Familiar Exposition of the Feudal System in the Middle Ages; with its Causes and Consequences.

A History of the French Revolution; its Causes and Consequences. Newly written for this Collection.

The Ruins of Rome and their Historical a.s.sociations; including an Account of the Modern City and its Inhabitants.

The Private Life, Manners, and Customs of the Ancient Romans. From the French of D'Arnay; carefully edited, and forming a valuable work for study or amus.e.m.e.nt.

Constantinople and its Historical a.s.sociations; with some Account of its Inst.i.tutions and the Manners and Customs of the People.

History of the Rise and Progress of the Trading Communities of the Middle Ages.

Trading Communities of Modern Times; a Popular View of the Origin, Structure, and General Tendency of the Joint-Stock Trading and Commercial Bodies of Modern Times.

The Ruins of Athens and their Historical a.s.sociations; with Notices of the Modern City and its Inhabitants.

A History of London, Ancient and Modern.

A History of the Endowed Schools of Great Britain.

The Incas of Peru, with some Account of the Ruins of their Greatness.

A popular History of the British Army.

A popular History of the British Navy.

II. Popular Biography.

One of the most useful and pleasing forms under which knowledge can be presented to the general reader is that of the Biography of distinguished men, who have contributed to the progress of that knowledge in some one or other of its various departments. But it too frequently happens, that the biographical notices of great men consist rather of personal, trivial, and unimportant details, than of a clear and broad outline of the influence which they exerted upon the pursuit and upon the age in which they were distinguished. The true object of Biography is, while tracing the progress of an individual, to show not only what result his active life has produced on the well-being of his fellow-men, but also the position which he occupies as one of the "great landmarks in the map of human nature."

Yet we are not satisfied with a biography which regards its subject in his public capacity alone: we are naturally curious to ascertain whether the same qualities which rendered him celebrated in public, followed him likewise into private life, and distinguished him there.

We regard with interest, in his private capacity, the man who has been the originator of much public good: we look with an attentive eye on his behaviour when he stands alone, when his native impulses are under no external excitement; when he is, in fact, "in the undress of one who has retired from the stage on which he felt he had a part to sustain."

But a detail of the public and private events in the life of a distinguished man, do not alone suffice to form a just estimate of his character. The reader requires to be made acquainted with the state of a particular branch of knowledge, at the time when the individual appeared, whose efforts extended its boundaries. Without this it is impossible to estimate the worth of the man, or the blessings and advantages conferred upon society by his means.

On the other hand, in tracing the history of any particular branch of knowledge, unless connected with Biography, we lose sight of individual efforts; they are mingled with the labours of others, or are absorbed into the history of the whole, and are consequently no longer individualized: hence we are likely to fail in recognising the obligations due to our distinguished countrymen, or to deprive of their just merit those of our foreign brethren, whose useful lives have influenced distant lands as well as their own.

With these views it is proposed that each Biography shall consist of three distinct portions:

1 The history of a particular department of knowledge, up to the time when the individual appeared by whom its boundaries were extended.

2 A _general_ sketch of the life of such individual, with _particular_ details of the improvements effected by him.

3 The progress of such branch of knowledge, from the date of such improvements up to our own times.

The following subjects will be immediately published:

Smeaton and Lighthouses.

Sir Joseph Banks and the Royal Society.

Sir Humphrey Davy and the Safety Lamp.