MECHANICS AND USEFUL ARTS. 115 



Powder enough to fill the cylinder is all that can be introduced into 

 the lock, and its explosion therein damages it no more than it would a 

 pistol barrel of the same size. 



This latter lock has attracted much attention. It is simple in its de- 

 tails, has no long trains of motions depending on each other, is not lia- 

 ble to get out of order, and has, when locked and unlocked by those 

 unacquainted with its operation, been productive of no little mirth. It, 

 as I have attempted to describe, fairly steals the bit away from the 

 handle, and leaves the latter only in the grasp of the astonished exper- 

 imenter, who, as he turns, finds the lock unlocked, but the key proper 

 gone, and every aperture in the lock completely closed. Until he is 

 undeceived, he' is apt to imagine that the whole affair is some juggler's 

 apparatus, constructed for his mystification, and not for legitimate use 

 as a door fastener. 



Either of the three locks thus noticed, when placed on doors which 

 have also been patented, and will now be described as intelligibly as is 

 in my power, appears to me to afford perfect security against all 

 known methods employed by burglars. 



The door first patented is constructed as follows, namely : by sup- 

 porting, at some fixed distance apart, and attaching to each other, two 

 plates of sheet iron, w T ith a rim between them, which, with the plates, 

 completely enclose a space and form a sort of iron box. Into this 

 space Xo. 3, or white pig, is poured when melted, which fills the space, 

 encloses the bolts which connect the sheets, and enters apertures 

 left in either of them. The whole forms a door in which the sheets 

 firmly support, and prevent the breaking of the thoroughly chilled 

 and hardened interior, while it in turn forms a complete stopper to all 

 drills and cutting tools which may, by burglars, be made to preforate 

 the outer sheet. 



In another door, invented to meet the same requisites, and to pre- 

 sent a bar to that class of ingenious operators whose acquisitiveness 

 has generally contrived ways to circumvent the utmost ingenuity of 

 the lawful dealing workman, pig-iron of the same character is cast 

 around a wrought iron gauze or net-work. This net-work is made of 

 the size of the intended door, with meshes about one and a half inch 

 square, and is constructed of bars of small round iron. All attack by 

 drilling is prevented by the chilled cast iron, and when the door is 

 assailed by a heavy sledge, this iron breaks into small pieces, each of 

 the size of a mesh, the fracture being along the centre line of the iron 

 rods, and each fragment being firmly held in place by the groove formed 

 by its junction with the bars which surround it. The door, by repeat- 

 ed blows, becomes pliable, yielding, and is bulged in here and there, 

 but the strongest man has not yet been able to make any absolute 

 break therein. 



Improvement in Propellers. An improvement in propellers has 

 been patented by a French inventor, whose object was partially to re- 

 move the resistance to the progress of the vessel under sail only, 

 which is occasioned by the ordinary screw propeller. This plan has 

 no relation to those which permit of alteration of the pitch, or admit 



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