MECHANICS AXD USEFUL ARTS. 73 



into the coral before inserting the foundation-piles. As this species of 

 rock is, however, too soft to bear the weight imposed upon each of 

 the foundation-piles, an expedient has been adopted by which a larger 

 area for support is obtained, and the weight of the entire structure made 

 to rest on the surface of the rock. This is accomplished by connecting 

 each foundation-pile with a large disk of cast-iron, and the disk rest- 

 ing on the surface, while the pile passes down through its centre 10 

 feet into the body of the rock, the two points of stiffness and support 

 are duly achieved. 



"The heads of the foundation-piles rises 15 feet above the surface of 

 the reef, and are there framed together by massive horizontal ties 

 keyed into appropriate sockets, from which rises a series of wrought- 

 iron pillars to the height of 30 feet, having an inclination towards the 

 centre of about 10 degrees. On the heads of these pillars are fitted 

 massive sockets, from which rises a second series of pillars, 33 feet 

 long, and of less diameter, the heads of which are also fitted with 

 sockets, that bear the third and upper series of pillars, 24 feet long. 

 A central column rises from the centre foundation-pile to a level with 

 the top of the upper series of pillars ; and from this central column 

 there radiate, at proper levels, iron girders of great strength, which, 

 added to the horizontal ties extending from one pillar to another, form 

 a combination so compact and stiff that no force of the wind, it is sup- 

 posed, will ever disturb it. 



" For the residence of the keepers of the light, a cast-iron dwelling, 

 of a circular and conical form, is fitted to the above-described frame- 

 work of pillars, ties, &c., at a point 35 feet above the level of the 

 reef, and 20 feet above the highest tides. This dwelling consists of 

 two stories. The lower one, being about 8 feet in height and 40 feet 

 in diameter, is designed for the deposit of stores, the kitchen, &c. 

 It is fitted with 8 windows, and 16 bull's-eyes, the former for air, 

 the latter for light. It contains 6 iron tanks, for water and oil. The 

 upper story is divided into 6 rooms, with a hall in the centre, to allow 

 a free ventilation in all the apartments. There is a door at each end 

 of the hall, and a large window in each room. Surrounding this story 

 is a gallery, exterior to the house, 5 feet in width, where the keepers 

 may exercise. 



' ; From the centre of the hall rises a spiral staircase to the top of 

 the structure. This staircase is inclosed by an iron cylinder, the 

 whole weight of which rests upon the roof of the dwelling-house. 

 On the top of the structure is the watch-room, and lantern, or light- 

 room, fitted to contain a catadioptric apparatus of the largest size, that 

 will produce a light of the highest power. The diameter of the struc- 

 ture at the base is 50 feet, and 20 feet at the level of the watch-room 

 floor. The height of the entire work above the surface of the reef 

 will be 127 feet, and the height of the centre of the light 115 feet. 

 The sight will be about 9 miles distant from the nearest land (Key Lar- 

 go), and the depth of water on the site at low tide about 8 feet. 



7 



