May 23, 1889] 



NATURE 



89 



to be in readiness for receiving the lantern and the illuminating 

 apparatus, and it was left with confidence to resist the storms of 

 the approaching winter. But during a very violent storm, between 

 11 p.m. of the 5th and 3 a.m. on the 6th of the following 

 February, the lighthouse was completely destroyed, and swept 

 from the rock. On further consideration of the matter, the 

 Trinity Ifouse determined, on the recommendation of their 

 engineers, to proceed with a stone structure, and my father was 

 appointed to build the lighthouse, I acting as before as assistant 

 engineer. The work was proceeded with in the spring of 185 1. 

 In order to obtain the greatest possible diameter of base for the 

 tower that the rock would admit of, it was found necessary to 

 lay a portion of the foundation on the most exposed side of the 

 rock, at the level of I foot below low water of spring tides ; and, 

 although every possible human effort was made by the leader 

 and his devoted band of workers, the foundations were not com- 

 pleted until the end of the season of 1852. Soon after this, my 

 brother, Mr. William Douglass, now Engineer- in- Chief to the 

 Commissioners of Irish Lights, succeeded me as assistant 

 engineer at the work. The lighthouse was completed in 1858, 

 and its dioptric fixed oil light of the first order was first exhibited 

 on September i of that year. Soon afterwards, its exposure to 

 heavy seas during storms was fully realized. On one occasion 

 the fog bell was torn from its bracket at the lantern gallery at 

 ICX3 feet above high water, and the flag-staff, with a ladder, 

 which were lashed outside the lantern, were washed away. 

 The tremor of the tower on these occasions was such as to 

 throw articles off shelves, and several of the large glass prisms 

 of the dioptric apparatus were fractured. After some time it 

 was found that several of the external blocks of granite situated 

 a few feet above high water were fractured by the excessive 

 strains on the building. In 1874 the tower was strengthened 

 from top to bottom by heavy iron ties, boiled to the internal 

 surface of the walls ; but, after a violent storm in the winter 

 of 1881, there was evidence of further excessive straining at the 

 face of the lower external blocks of masonry, when the Trinity 

 House, on the advice of their engineer, determined on the re- 

 erection of the lighthouse. This was accomplished (as 

 shown in Fig. i) by incasing the existing tower with carefully 

 dovetailed granite masonry, each alternate block of the new 

 granite being dovetailed to the old. The work 

 was one of considerable difficulty, owing to the 

 necessity for maintaining the light throughout the 

 progress ; and the risk to the workmen was great, 

 especially at the upper part of the old tower, owing 

 to the narrow ledge on which the work had to be 

 executed. I am, however, thankful to state that 

 the new lighthouse has been successfully completed 

 by my son, Mr. W. T. Douglass, who was also my 

 assistant engineer at the Eddystone ; and with the 

 same complete immunity from loss of life or limb 

 to any person employed, as with the two previous 

 stnictures on this rock. The optical apparatus con- 

 sists of two superposed tiers of lenses of the type 

 adopted at the Eddystone, but of larger dimensions, 

 as suggested by the late Mr. Thomas Stevenson, 

 for obtaining greater efficiency with the larger- 

 flame luminaries recently adopted. The apparatus 

 is provided with two Trinity House improved 

 mineral oil burners, and has a minimum intensity 

 for clear weather of about 80,000 candle units, and 

 a maximum intensity for thick weather of about 

 513,000 candle units. The character of the light is 

 double- flashing, showing two flashes, each of four 

 seconds' duration, in quick succession, at periods of 

 one minute. The flashes of this light, and those 

 of a light lately corhpleted at about 8 nautical 

 miles from it, on Round Island, are the most 

 intense yet attained with oil flames for beacon lights ; and 

 it may be stated that, with no other illuminant at present 

 known to science could these results be carried out within the 

 space available at the Bishop Rock, and under the circumstances 

 attending that work. The fog signal recently adopted at this 

 station, in lieu of the bell, is by the electrical explosion of 

 4-ounce charges of gun-cotton, at intervals of 5 minutes. The 

 apparatus provided for this form of fog signal is shown in 

 Fig. I. It consists of a wrought- iron crane (attached to the 

 lantern) which is raised and lowered by a worm-wheel and 

 pinion. When the crane is lowered, its end reaches near the 

 gallery, where the lightkeeper suspends the charge of gun- 



cotton, with its detonator attached, to the electric cable, which 

 is carried along the crane and through the roof of the lantern to 

 a dynamo-electric firing machine. After suspending the charge^ 

 the jib of the crane is raised to its upper position, when the 

 charge is fired nearly vertically over the glazing of the 

 lantern, and thus without causing damage to it. The 

 large and heavy optical apparatus is rotated automatically 

 by compressed air, which is stored in two vertical steel reser- 

 voirs, fixed at the centre of the tower. The air is compressed 

 by a small Davey safety motor. A Vi'inch, worked by the 

 compressed air, is fixed on the lantern gallery for landing the 

 lightkeepers, stores, &c. Fig. 2 is a sketch, from actual obser- 



FJC.2 



vation, of the height and form of waves on the tower during a . 

 storm. 



The numerous outlying shoals surrounding the shores of this 

 country, particularly off the east coast, were an early cause of 

 anxiety to those responsible for the guidance of mariners. And 

 in addition to buoys as sea-marks by day, floating lights, as 

 guides by night, were found to be a necessity. The first light- 

 vessel was moored at the Nore Sand in 1732, and another near 

 the Dudgeon Shoal in 1736. We have here a model of the 

 latter vessel, from which we may judge of the pluck and hardi- 

 hood of the crews who manned them, especially when we 

 remember that there were no chain cables in those days, the 



Foff.3 



vessel having to be moored with a cable of hemp, which, owing 

 to the constant chafing, occasionally parted during winter 

 storms, when, to save their lives, the crew had to put out 

 another anchor if possible, or set such storm canvas as they 

 could to keep her off a lee-shore, and endeavour to reach a place 

 of safety. The illuminating apparatus of these vessels consisted, 

 of a sujall lantern and flat-wick oil lamps, fixed at a yardarm, 

 and here appears to have occurred the first application of a 

 distinctive character to beacon lights, for the Dudgeon was fitted 

 with two lights, one being placed at each arm of the yard (Fig. 3). 

 The next light- vessel was placed at the Newarp Shoal in 1 790, and 

 in 1795 one was placed at the north end of the Goodwin Sands.. 



