LIGHT since examined by others, particularly by Bunsen and Roscoe, whose experiments, to- gether with other matter pertaining to. the subject, will be found in the articles PHOTOME- TRY and PHOTOGRAPHY. For a more extended consideration of the subject of light, see tlje treatise on the undulatory theory of light by President F. A.' P. Barnard, published in the Smithsonian report for 1862; an "Essay on the Velocity of Light," by M. Delaunay, trans- lated by Alfred M. Mayer, in the Smithsonian report for 1864 ; CEuvres completes cPAugustin Fresnel (3 vols., Paris, 1867-'70); Wtillner's LehrbucJi der Experimental PJiysik (vol. ii., Leipsic, 1871); and "The Wave Theory of Light," by Humphrey Lloyd, D. D., D. C. L. (London, 1873). LIGHT, Aberration of. See ABERRATION. LIGHT, Zodiacal* See ZODIACAL LIGHT. LIGHTFOOT, John, an English clergyman, born in Stoke-upon-Trent, March 29, 1602, died in Ely, Dec. 6, 1675. He was educated at Christ's college, Cambridge, and became chaplain to Sir Rowland Cotton, a celebrated Hebrew scholar, who inspired him with a desire to become one also. Anxious to prosecute his studies, he re- moved to Hornsey, near London, where he could have access to libraries. In 1629 he published "Erubhim, or Miscellanies, Christian and Judaical," and dedicated it to Sir Rowland, who presented him to the rectory of Ashley in Staffordshire. In 1642 he was appointed minister of St. Bartholomew's in London, and a member of the assembly of divines sitting at Westminster. Shortly after he was made master of Catharine hall, Cambridge, and pre- sented to the rectory of Great Munden in Hertfordshire. In 1655 he was chosen vice chancellor of the university, and after the res- toration a prebendary of Ely. Lightfoot was a very learned Hebraist for his time, and was remarkable for his intimate acquaintance with rabbinical literature. One of his most impor- tant works, HortE HebraicoB et Talmudicm (Cam- bridge, 1648), has been reedited by R. G and ell (4 vols., Oxford, 1859). At the time of his death he was engaged on the " Harmony of the New Testament." The first collected edi- tion of his works appeared in 1684; the best edition of them is that of the Rev. J. R. Pit- man (13 vols. 8vo, London, 1822-'5). LIGHTFOOT, Joseph Barber, an English cler- gyman, born in Liverpool in 1828. He was educated at Trinity college, Cambridge, where he graduated in 1851, was elected fellow in 1852, took orders in 1854, and became tutor of Trinity college in 1857. He was also appoint- ed honorary chaplain to the queen and Hulsean professor of divinity in the university in 1861. A few years later he became examining chap- lain of the archbishop of Canterbury, and in 1871 was made canon residentiary of St. Paul's cathedral, London. He has published " St. Paul's Epistle to the Galatians" (1869), "The Two Epistles to the Corinthians of St. Clement of Rome" (1869), "St. Paul's Epistle to the LIGHTHOUSE 453 Philippians" (1870), each with revised text, notes, &c. ; also an essay "On a Fresh Re- vision of the English New Testament" (1871). LIGHTHOUSE, a structure from the top of which a light is shown at night as a direction or warning to mariners. Lighthouses are ne- cessarily situated on headlands, isolated rocks or sands, and pierheads ; and from the benev- olence of their design, and in many instances from the boldness of their construction, they have always been objects of interest indepen- dently of their use to mariners. We propose to treat the subject under the following divi- sions : 1, materials and mode of construction ; 2, method of illumination ; 3, auxiliary safeguards to navigation; 4, history and statistics. 1. MATERIALS AND MODE OF CONSTRUCTION. The materials used in the construction of light- houses are wood, stone, brick, cast iron, and wrought iron. Stone, brick, and iron are the most important, and are used exclusively in all large lighthouses. The most noted lighthouses in the world are built of stone ; and in north- ern climates, where the first cost is not the great consideration, stone should be exclusively used. The form of all stone lighthouses ap- proaches more or less the frustum of a cone or pyramid. They are sometimes built to include the keepers' apartments, but more usually they merely contain the staircase and cleaning and watch rooms, with a receptacle for the oil butts. In all cases where large lighthouses are built of this material, the masonry should be of the best cut stone with hydraulic cement mortar. The first cost should never be so lim- ited that this principle cannot be fully carried out. The same principle applies to brick light- houses, which should be built of the best and hardest bricks, laid in hydraulic cement mor- tar. The interior walls of all lighthouses should be as separate as possible from the outer walls, in order that there may be a free circulation of air between the walls. The dryness of the inner wall is insured by this arrangement, with- out which all large masses of masonry like large lighthouses must be constantly damp. The in- ner wall must of course be firmly tied to the outer shell by masonry or iron ties. Cast-iron lighthouses were first erected by Mr. Alexan- der Gordon, an English civil engineer. Two were constructed in England, and were erected on the islands of Bermuda and Jamaica. From the fact that every part of the structure can be completed at the workshop, cast-iron light- houses answer admirably for positions at points remote from large centres of manufacture, and are gradually coining into use. Several light- houses of this kind have been erected at vari- ous places on the coasts of the United States. They require a lining of brick, the weight of which prevents oscillation or swaying, while its low conducting power of heat hinders the deposition of moisture on the well room of the stairs, which would otherwise be occasioned by the difference of temperature between the inside and outside of the tower. To further
