Antoine de GUISCARD was a French adventurer, whose private life had been marked by great profligacy. He had taken an obscure part in the insurrection of the Cevennes—rather as a recruiting agent than as a combatant. In that character he had met with encouragement to raise a refugee regiment in England. Hopes had also been held out to him that a British auxiliary contingent would be landed on the southern coast of France. In the course, however, of some preliminary inquiries into the position of the insurrectionists, it was found that such an invasion would have little chance of any useful result, and the project was abandoned. Meanwhile, a pension of £400 a year had been bestowed on the emissary. But ere long it was discovered that GUISCARD had profited by opportunities, afforded him in the course of the discussions about the proposed expedition, to make himself conversant with many particulars of military and naval affairs, and that it was his habit to send advices into France. Some of his letters were seized. Their writer was arrested on the 8th of March, 1711, and was taken, immediately, before a Committee of the Privy Council. When examined as to his illicit intercourse with France he persisted in mere denials. At length, one of his letters was shown to him by HARLEY, and he was closely pressed as to his motives in writing it. He then addressed himself to Secretary ST. JOHN, and begged permission to speak with him apart. The Secretary answered, ‘You are here before the Council as a criminal. Whatever you may have to say must be said to all of us.’ The man persisted in refusing to reply to any further questions, unless his request was granted. Seeing that nothing more could then be obtained from him, the Lord President rose to ring the bell for a messenger, that the prisoner might be removed in custody. At that moment the prisoner pulled a penknife from his pocket, turned towards HARLEY, near to whom he stood, and stabbed him in the breast. He repeated the stroke, and then rushed towards ST. JOHN. But between the prisoner and the Secretary there stood a small table, over which he stumbled. ST. JOHN drew his sword, and, with the words ‘The villain has killed Mr. HARLEY,’ struck at him, as did also the Duke of ORMOND and the Duke of NEWCASTLE. Lord POWLETT cried out ‘Do not kill him.’ Presently the assassin was in the hands of several messengers, with whom, notwithstanding his wounds, he struggled so desperately that more than one of them received severe injuries. When at length overpowered, he said to ORMOND, ‘My Lord, why do you not despatch me?’ ‘That,’ replied the Duke, ‘is not the work of gentlemen. ’Tis another man’s business.’