Archibald Campbell, Earl of Isla, was younger brother of the admired John, Duke of Argyle, whom he succeeded in the title, and with whom he had little in common, but the love of command. The elder brother was graceful in his figure, ostentatious in big behaviour, impetuous in his passions; prompt to insult, even where he had wit to wound and eloquence to confound; and what is seldomer seen, a miser as early as a hero. Lord Isla was slovenly in his person, mysterious, not to say with an air of guilt in his deportment, slow, steady where suppleness did not better answer his purpose, revengeful, and if artful, at least not ingratiating. He loved power too well to hazard it by ostentation, and money so little, that he neither spared it to gain friends or to serve them. He attained the sole authority in Scotland, by making himself useful to Sir Robert Walpole, and preserved it by being formidable to the Pelhams. The former had disgusted the zealous Whigs in Scotland by throwing himself into the arms of a man of such equivocal principles: the Earl pretended to return it, by breaking with his brother when that Duke quarrelled with Sir Robert: yet one chief cause of Walpole's fall was attributed to Lord Isla's betraying to his brother the Scotch boroughs entrusted to his management in 1741. It must be told, that Sir Robert Walpole always said, he did not accuse him. Lord Isla's power received a little shock by Lord Tweedale's and Lord Stair's return to Court on that Minister's retreat; but like other of Lord Orford's chief associates, Lord Isla soon recovered his share of the spoils of that Administration. He had been ill with the Queen (of whom he knew he was sure while he was sure of Sir Robert Walpole) from his attachment to Lady Suffolk: he connected with Lord Granville, while Lord Granville had any sway; and as easily united with the Pelhams, when power was their common pursuit, and the humiliation of the Duke and the Duke of Bedford the object of their common resentment; for common it was, though the very cause that naturally presented them to the Duke of Argyle's hatred, their zeal and services, ought at least to have endeared them to the brothers.
By a succession of these intrigues, the Duke of Argyle had risen to supreme authority in Scotland: the only instance wherein he declined the full exertion of it was, when it might have been of service to the master who delegated it; in the time of the Rebellion: at that juncture he posted to London: the King was to see that he was not in Rebellion; the Rebels, that he was not in arms. But when this double conduct was too gross not to be censured, he urged a Scotch law in force against taking up arms without legal authority; so scrupulously attached did he pretend to be to the constitution of his country, that he would not arm in defence of the essence of its laws against the letter of them. In his private life, he had more merit, except in the case of his wife, whom having been deluded into marrying without a fortune, he punished by rigorous and unrelaxed confinement in Scotland. He had a great thirst for books; a head admirably turned to mechanics; was a patron of ingenious men, a promoter of discoveries, and one of the first great encouragers of planting in England; most of the curious exotics which have been familiarized to this climate being introduced by him. But perhaps too much has been said on the subject of a man, who, though at the head of his country for several year, had so little great either in himself or his views, and consequently contributed so little to any great events, that posterity will probably interest themselves very slightly in the history of his fortunes.