LIGHT LIGHTHOUSES. 



The concentrated light of the moon, like tlmt of the 

 gases, produced no change. The importance of 

 light to plants is well known : deprived of it, they 

 become white, ami contain an excess of saccharine 

 and aqueous particles : and flowers owe the variety 

 and intensity of their hues to the influence of the 

 solar beams. Even animals require the presence of 

 the rays of the sun, and their colours seem materially 

 to il.'i'i'iul upon the chemical influence of these rays. 

 A comparison between the polar and tropical ani- 

 mals, and between the parts of their bodies exposed, 

 ami those not exposed to light, shows the correctness 

 of this opinion. (For an account of the physical 

 affections, and other chemical effects of light, see 

 Optics, Phosphorescence, and Polarization of Light.) 



LIGHT, ABERRATION OF. See Aberration. 



LIGHT, DIFFUSION OF ITS PARTICLES. See Divi- 

 tibility. 



LIGHT CAVALRY, or HORSE. See Cavalry. 



LIGHTER; a large, open, flat-bottomed vessel, 

 employed to carry goods to or from a ship. 



LIGHTFOOT, JOHN, a learned English divine, 

 born in Staffordshire, in 1602, and received his educa- 

 tion at Christ-church, Cambridge. He made extra- 

 ordinary advances in the Greek and Latin languages, 

 and became curate of Norton-under-Hales. Sir 

 Rowland Cotton made Mr Lightfoot his chaplain, 

 and took him into his house, where he applied him- 

 self to Hebrew with singular assiduity and success. 

 In 1629, he printed his first work, entitled Erubhim, 

 or Miscellanies, Christian and Judaical, which he 

 dedicated to Sir Rowland Cotton, who presented 

 him to the vicarage of Ashley, in Staffordshire. 

 Here he resided until his appointment as one of the 

 parliamentary assembly of divines rendered it neces- 

 sary for him to remove to London. He warmly 

 pressed the speedy settlement of the church, in the 

 presbyterian form. In 1655, he became vice-chan- 

 cellor of Cambridge, and zealously promoted the 

 Polyglot Bible. After the restoration, he was 

 appointed one of the assistants at the Savoy confer- 

 ence, where he, however, attended but once or twice, 

 S'ving all his attention to the completion of his 

 armony. He died Dec. 6, 1675. The works of 

 Dr Lightfoot, who, for rabbinical learning, has had 

 few equals, were printed in 1684, in 2 vols., folio ; 

 and again, with additions, at Amsterdam, in 1686 ; 

 and by Leusden, at Utrecht, 1699, in 3 vols. An 

 octavo volume of his remains was also published by 

 Strype, which contains some curious particulars of 

 his private life. 



LIGHTHOUSES were in use with the ancients. 

 The towers of Sestos and Abydos, the colossus of 

 Rhodes, the well-known tower on the island of 

 Pharos, off Alexandria, are examples. Suetonius 

 also mentions a lofty tower at Ostia, and another on 

 the coast of Batavia, erected for the purpose of guid- 

 ing the mariner by their light. In lighting a great 

 extent of coast, it becomes necessary to provide for 

 the distribution of the lighthouses in such a manner 

 that they may be readily distinguished from each 

 other, and, at the same time, so disposed as not to 

 leave vessels without some point by which to direct 

 their course ; and, in constructing each member of 

 the series, care should be taken to provide for a 

 sufficient brilliancy of light, and for means of dis- 

 tinguishing each lighthouse from every other, as well 

 as from other lights on shore or in ships, or in the 

 heavens. The best constructed lighthouses, in Great 

 Britain, are fitted up with parabolic reflectors, con- 

 sisting of a circular sheet of copper, plated with 

 silver, in the proportion of six ounces to each pound 

 of copper, and formed into a parabolic curve, by the 

 assistance of a gauge, by a very nice process of ham- 

 merine. The reflector, thus shaped, is then polished 



with the hand. An Argand lamp is placed in the 

 focus of the paraboloidal surface, and the oil is sup- 

 plied by tlie lamp behind. But the disadvantages of 

 this mode are acknowledged ; such as the loss of 

 light, partly from its absorption by the reflector, and 

 partly from the collision of the rays; the impossibility 

 of increasing the intensity of the light in dark and 

 hazy weather ; the difficulty of forming distinguish- 

 ing lights, &c. The important invention of the 

 polyzonal lenses, in which refraction is employed 

 instead of reflection, seems, therefore, likely to super- 

 sede the use of reflectors. This subject is treated by 

 Brewster (Transactions of the Royal Society of Edin- 

 burgh, vol. xi.), and by M. Fresnel, in a memoir 

 read before the academy of sciences at Paris Sur an 

 nouveau Systeme d'Eclairage des P hares (1822) 

 and the imperfections of the parabolic reflectors, and 

 the superiority of the polyzonal lenses over others, 

 are explained. Another important problem is the 

 construction of distinguishing lights, so that the 

 mariner may not be deceived in taking one light- 

 house for another. Single and double stationary 

 lights, or lights disposed in different forms, were first 

 employed ; revolving lights were next adopted, 

 which appeared and disappeared at intervals ; and 

 these are sometimes exhibited double or triple. The 

 lights may be so disposed as only to illuminate the 

 safe channel. Difference of colour is sometimes 

 made use of as a distinction. It sometimes becomes 

 desirable, as in hazy weather, to produce a very 

 intense light. A plan was proposed, to effect this 

 object, by lieutenant Drummond (Philosoph. Trans. , 

 1826), by directing upon a ball of chalk, a quarter 

 of an inch in diameter, three alcoholic flames,by means 

 of a stream of oxygen. The employment of gas, in 

 lighthouses, has also been recommended. 



Floating Light differs from the preceding, by its 

 being erected on board a vessel, which is strongly 

 moored upon a sand or shallow, to warn ships 

 against approaching it. 



A select committee of the house of commons was 

 appointed early in the year 1834 to inquire into the 

 present state of British lighthouses ; and the follow- 

 ing are the views of the directors as stated in their 

 petitions to parliament, and as recorded in the min- 

 utes of the committee : 1. That all private concern 

 in lighthouse property should cease. 2. The exclu- 

 sive appropriation to lighthouse purposes of all funds 

 collected in name of lightmoney. 3. Collections to 

 be limited to the amount required for lights. 4. 

 No exemptions from payment of dues by vessels 

 using the lights; and that steamers, coasting and 

 fishing vessels, be taxed at less rates than oversea 

 vessels. 5. Collection of the dues in the hands of 

 government. 6. A consolidation of the boards, and 

 a uniform scale of rates applicable to the whole 

 United Kingdom and 7. A reduction of expense, 

 and the rates generally. la addition to the above 

 suggestions, the directors recommended the trial of 

 an experiment in the hands of government to prove 

 the merits of the lens system of' illuminating light- 

 houses, as now extensively practised in France, in 

 comparison with that of parabolic reflectors, used 

 hitherto in this country. The experiments at Gul- 

 lane Point were not such as to put this long dis- 

 puted matter fully at rest. On these occasions, 

 lights were applied to the foci of individual lenses 

 only, without the assisting apparatus of subsidiary 

 lenses and mirrors, as described in the work of M. 

 Fresnel. From a correspondence entered into with 

 scientific men in this country and France, and like- 

 wise from the obvious leaning of the different boards 

 to the old system, the directors were convinced of 

 the expediency of conducting an experiment in the 

 hands of neutral persons ; and subsequent compari- 



