MECHANICS AND USEFUL ARTS. 67 



over the gate or door. Attached to the top of the gates are two 

 wheels, which rest immediately on the top of the bar mentioned. 

 When it is necessary to open the gates or door, the bar is raised a lit- 

 tle in the centre of the doorway by turning a key round and round, 

 which unlocks the gate, and at the same time raises the bar suffi- 

 ciently to form an inclined plane, upon which the gate or door, by 

 means of rollers or wheels, runs back by its own gravity, into a suit- 

 able recess in the piers or wall at each side, and thus opens the gate- 

 way clear of all obstruction. When it is desired to close and lock 

 the gates, the bars upon which they hang are depressed a little at the 

 ends, and the gates run along the bars until the gateway is closed. 

 The London and Northwestern Railway Company have adopted this 

 plan at one of their stations, and find it to answer much better than 

 the ordinary mode, but one man being needed to open and shut the 

 gates, while by the ordinary plan it required six. It is recommended 

 to be used in all cases, from the ponderous gates of a fortress or rail- 

 way station down to the highly finished door of a mansion. Hera- 

 path's (London) Journal. 



EFFLUVIA-TRAP. 



MR. C. MARSDEN has invented an effluvia-trap, which well'answers 

 its purpose. It consists of a drum, with four receivers or buckets, 

 caused to revolve by the weight of the matters falling into one of 

 them, when it instantly empties itself, and another bucket, is ready to 

 take its place. It is impossible for this trap to get choked up or for 

 any effluvia to escape. Civil Engineer and Architect's Journal, June. 



NEW RAT-TRAP. 



AMONG the patents issued in June last is one for an invention by 

 Mr. Stevens of Maryland, whereby he has endeavoured to bring the 

 science of optics to aid him in constructing a trap for catching rats. 

 In this new trap a mirror is so arranged that the rat which looks at 

 the bait shall see his own image reflected in such a position as will 

 lead him to believe that a second rat is trying to get before him in 

 seizing the bait ; and when the first rat has been caught, his image 

 will be reflected by a mirror, so that the next rat who shall look at 

 the bait shall see two rats apparently striving to seize it, thus decoy- 

 ing him upon the turning table, which yields to his weight and pre- 

 cipitates him into the body of the trap. 



MANUFACTURE OF GOLD PENS. 



THE' following interesting history of the origin and description of 

 the process of manufacturing gold pens we copy from the New York 

 Tribune : 



" Mr. John Isaac Hawkins, an American by birth, though for nearly 

 forty years a resident of Europe, claims the original invention of the 

 project of so forming a pen from gold as to render its point, or nib, 



