During the last few months, several of the ordinary iron sales have been burglariously opened in London and Manchester, by means of a powerful instrument employed by the thieves in cutting large, holes through the iron doors, whereby they have gained acGess to the works of the lock. The construction and operation of the instrument were unknown until a few weeks since, when, happily, one of them, with all its loose appliances, was secured by the police. It would be obviously wrong to publish a description of the apparatus; but, having inspected it minutely, and seen it in operation, we are enabled to state that great ingenuity and mechanical skill have been bestowed upon its contrivance. Of course the discovery has rendered a counter improvement in the safe itself absolutely essential to security ; and it is with much pleasure that we are in a position to announce the introduction of such an improvement. By the courtesy of the Metropolitan Police authorities, Mr. Chubb, the eminent lock and safe manufacturer, of St. Paul's Churchyard, has been allowed to examine and experiment with the instrument, and he has succeeded completely in providing a simple method of baffling its operation. The improvement consists in placing throughout that portion of the door which is in front of the lock, a number of hardened screwed steel plugs, sufficiently close to each to prevent either an ordinary drill or circular hollow cutter from passing through without encountering several of the plugs. These plugs of hardened steel have the effect of utterly destroying the edge of every description of cutter which can be used with the burglar's apparatus, and consequently render the safes secure from its operation. All Chubb's fire-proof safes and "strong-room" doors are now made with the above improvement, and old safes may readily have it applied. It has been protected by Letters Patent.—London Mechanics' Magazine