"The operations of Roberts have been mainly confined to Philadelphia, in the suburbs of which city his "money mill" was situated. The last counterfeit pieces which he made, and which, in an indirect manner, led to his arrest, were copies of the latest issue of fifty cent postal currency. They are of steel, and the impression from them is so beautiful and perfect, as to be entirely undistinguishable from that of the genuine plates. Upon this counterfeit the criminal artist had exerted his skill with the most elaborate patience and precision, intending to make it, in every sense, a _perfect_ resemblance, which would even escape the suspicion of the Government detectives. "But though an engraver, Roberts was not a printer. His plate was perfection, but unaided, or assisted only by mediocre printers, he could not produce an impression equally perfect. He therefore left Philadelphia a short time ago to seek the services of a Brooklyn printer, whom he understood to have been in the counterfeiting business, and who was well known to be a mechanic of extraordinary skill. Unluckily for the English operator, this printer was in the service of the Government detectives, who were, therefore, promptly informed of the whereabouts of the game for which they had so long been in pursuit. "Messrs. Lowell and Otto, McWatters and others, accordingly surprised Roberts in his Brooklyn retreat, on Tuesday morning last, at 9-30. The counterfeiter made a desperate resistance, swearing that he would die sooner than be taken; but the detectives were too many for him. He was knocked down, disarmed, and speedily lodged in the Raymond Street jail. "The arrest was kept a profound secret, to allow the detectives time to effect the seizure of the plates and counterfeit money already manufactured in Philadelphia, which they were unable to do prior to the arrest. They also knew of twenty thousand dollars in the fraudulent currency, which the manufacturer had brought with him to Brooklyn, and which they hoped to procure. After lodging their prisoner in confinement, they immediately set out for Philadelphia, found the mill, and seized its contents, comprising the plates, tools, presses, fifty thousand dollars' worth of the fraudulent currency, all in fifty cent postage stamps. Some of it was in an unfinished state, but the detectives declare that the completed issues would have deceived them instantly; that they would never have doubted their genuineness. But they were outwitted by the prisoner, so far as the counterfeits in Brooklyn were concerned. During the absence of his captors, Roberts managed to have the following letter conveyed to his mistress and confederate:-- "'BROOKLYN, November --, 1865.