MECHANICS AND USEFUL ARTS. 69 



two ill-judged arrangements of the keeper had undoubtedly much in- 

 fluence in contributing to its destruction. The following conclusions, 

 respecting the manner of the destruction of the light, are thus stated 

 by Capt. Swift, after a minute inquiry into all the circumstances con- 

 nected Avith it. " Ten hours before the light fell, the platform, which 

 the keeper had placed on the second series of braces, 40 feet above the 

 rock, was washed off and came ashore. This platform was 43 feet 

 above the line of low water, and 28 feet above high water, spring 

 tides. Without undertaking to speculate upon the probable shock 

 which the structure must have received from the effect of the sea upon 

 a platform fastened to the piles 40 feet above the rock, it is enough to 

 know that at that time the sea had reached within seven feet of the 

 body or solid part of the structure. The sea was still increasing (the 

 effect of the continued gale) ; the nest tide was full about midnight, 

 and it required but a slight increase in the height of the wave or sea, 

 after having reached the second tier of braces, to bring it in con- 

 tact with the main body of the structure. When this took place, it is 

 plain to perceive that such a sea, acting upon the surface of the build- 

 ing, at the end of a lever, 50 or GO feet long, must be well nigh irresist- 

 ible ; and I doubt not that the light-house was thus destroyed. The 

 conclusions I arrive at, therefore, are these : 1st. That the sea did reach 

 the main body of the structure. 2d. That the platform placed by the 

 keeper on the second series of braces, contrary to the design of the 

 builder of the light-house, contributed to the overthrow. 3d. That the 

 five and a half inch hawser, attached to the top of the light, and ex- 

 tending 300 feet north-west, or in a direction directly at right angles 

 with the direction of the sea, north-east, had a most injurious tendency, 

 and that it was enough in itself to cause the overthrow of the light- 

 house, had the sea not reached the body of the structure. It is easy to 

 perceive that the force of such a sea upon 300 feet of a hempen rope, 

 of five and a half inches, must have been immense, when the rope was 

 attached to the weakest part of the building, 60 feet above the rock." 

 It is the opinion of Capt. Swift, that a stone structure, like the Eddy- 

 stone, for want of sufficient base, cannot be made to stand upon the 

 Minot, and that the pile light destroyed was as firmly constructed as 

 circumstances would admit. 



STONE AND IRON CONGLOMERATE FOR LIGHT-HOUSES, ETC. 



ONE great item of expense in the erection of light-houses, in exposed 

 and difficult situations, as the Bell-Rock and Skerry vore edifices, has 

 been the peculiar form to which it was found necessary to shape the 

 blocks of stone, in order to make them self-sustaining, and to prevent 

 lateral motion or lifting. Without going into the details of the various 

 devices for connecting the blocks, it may be stated that eacli was of a 

 double dove-tailed form, so as to interlock with those within and out- 

 side of it in the same course. In order to materially reduce the ex- 

 pense of such arrangements, the following plan has been proposed by 

 Mr. George Knight, of Cincinnati : 



By filling broken granite into a mould of any desired form, and pour- 



