VOL. XXXir.] PHILOSOPHICAL TRANSACTIONS. 577 



two load -stones, which I had then in the house, and it was so hard that no file 

 would touch it.* 



An Account of the Manner of bending Planks in his Majestfs Yards at Dept- 

 ford, &c. by a Sand-heat, invented by Captain Cumberland. By Robert 

 Cay, Esq. N'^S?!, p. 75. 



The place, where the planks lie to be softened in the stove, is between two 

 brick-walls, of such a length, height, and distance from each other, as suffice 

 to admit the largest, or to hold a good number of the smaller sort: the bottom 

 is of thick iron plates, supported by strong bars; under the middle of which, 

 are two fire-places, whose flews carry the flame towards the ends. 



The planks are laid in sand ; the lowest about 6 or 8 inches above the iron- 

 plates; they are well covered with the sand, and boards laid over all, to keep 

 in the heat. The sand is moistened with warm water, for which purpose they 

 have a cauldron adjoining to the stove; and if the timber be large, and in- 

 tended to be very much bent, so that it must lie long in the stove, they water 

 the sand again, once in 8 or 10 hours. When it is judged to be soft enough, 

 the sand is removed ; and the workmen carry away their respective planks, to 

 the several places, where they are to be used; and having first nailed a thin 

 board on the outside, to preserve the plank from bruises, they fix one part in 

 its proper place, and bring the others to, by any power they can most conve- 

 niently apply. This work seems to be performed with great ease. 



This method excels that of burning the planks over an open fire, in several 

 respects: particularly, that no part of the wood is destroyed, but remains of 

 the same dimensions; at least very nearly; a plank of the breadth of l6 inches 

 being said not to alter above -^ part of an inch. The edges of the plank are 

 preserved; and consequently the work must be much firmer, and the caulking 

 last longer. The extraordinary softness of the wood, while warm, makes it 

 easily bend to any figure necessary in ship-building, which it holds very well, 

 if they have occasion to take it off again after it is cold: whereas the plank 

 bent by burning, would start when loosened; and could only be fixed to the 

 timbers by such a force, as was able to overcome the resistance occasioned by 

 the spring of the plank. It likewise adapts itself very readily to the surface of 

 the timbers, if they happen to be uneven. 



The gun deck-clamps in a ship of the second rate, which are very large 



* It is extraordinary that the latter piece of the iron was found to be magnetical and the former 

 not. On this account the case is doubtful. It is to be suspected that the workman had imposed on 

 the old gentleman, by getting the latter piece magnetized before he brought it. 



VOL. VI. 4 E 



