Many efforts were made for his release, the most efficacious by the Queen of France. It should have been the Dowager Marie de Médicis, in memory of her hot flame for him when he was a youth; but though she may have initiated the appeal, she died before his release, which he seems to have owed to Anne of Austria's good services. Freedom meant banishment, but this sentence he did not take very seriously. In these years he was continually going and coming between France and England, now warned by Parliament, now tolerated, now banished, again daring return, and escaping from the net. "I can compare him to nothing but to a great fish that we catch and let go again; but still he will come to the bait," said Selden of him in his Table-Talk.
Exile in Paris provided fresh opportunity for scientific study, though his connection with the English Catholic malcontents, and his services to the Queen Henrietta Maria, who now made him her Chancellor, absorbed much of his time. When the Cause needed him, the Cavalier broke away from philosophy; and in 1645 he set out for Rome, at the bidding of the Queen, to beg money for her schemes. With all his address, diplomacy was not among the chief of his talents. With high personages he took a high tone. Innocent X gave 10,000 crowns to the Cause; but they quarrelled; and the Pope went so far as to accuse Digby of misappropriation of the money. Digby, a man of clean hands, seems to have taken up the Queen's quarrel. She would have nothing to do with Rinuccini's Irish expedition, which his Holiness was supporting; and her Chancellor naturally insisted on disbursing the funds at her commands rather than at the Pope's. Moreover, he was now renewing his friendship with Thomas White, a heretic Catholic priest, of several aliases, some of whose work had been placed on the Index. White was a philosophic thinker of considerable power and subtlety, and he and Digby acted and reacted on each other strongly—though Digby's debt is perhaps the greater. Their respective parts in the Two Treatises and in the Institutionum Peripateticorum libri quinque, published under White's name, but for which Sir Kenelm is given the main credit, can hardly now be sifted. White, at all events, was not a prudent friend for an envoy to the Holy See. Digby "grew high and hectored with his holinesse, and gave him the lye. The pope said he was mad." Thus Aubrey. Henrietta Maria sent him once more on the same errand; but the Roman Curia continued to look on him as a "useless and restless man, with scanty wisdom." Before returning, however, he paid a round of visits to Italian courts, making everywhere a profound impression by his handsome person and his liveliness. He had to hasten back to England on his own business. His fortunes were desperate; and he desired to compound for his estates.
A week or so after the King's death he is proved by his correspondence to be in France, having fled after one more pronouncement of him as a dangerous man. He went into exile this time with a sad heart; and it was not only the loyalist in him that cried out. The life of an English country gentleman would never have satisfied him; yet he longed for it now it had become impossible. He writes from Calais to a friend: "Those innocent recreations you mention of tabors and pipes, and dancing ladies, and convenient country houses, shady walks and close arbours, make one sigh to be again a spectator of them, and to be again in little England, where time slides more gently away than in any part of the world. Quando sia mai ch'a rividerti io torno?"
He went this time knowing better than his fellow royalists the meaning of events. He was still a rank, but at least an intelligent, conspirator. English correspondents at Rouen and Caen report him in the company of one Watson, an Independent; and that he is proposing "to join the interests of all the English papists with the bloody party that murdered the king." Dr. Winsted, an English doctor in Rouen, asked him with indignation how he could meditate going back to England, "considering the abomination of that country." Digby replied that he was forced to it. "If he went not now he must starve." He plainly saw who was the real and only force in England; and he was going to make a bargain with the strong man for himself and his co-religionists. As a matter of fact there is no trace of his return at this moment. Not merely was his property in danger, but his head as well. Yet he never repented of his policy, and he carried it out, so far as might be, in his dealings with Cromwell a few years later. And Henrietta Maria bore him no grudge on this score.
Exile in Paris meant friendly intercourse with, and consolation of the Queen, but also scientific research. In 1651 Evelyn was visiting him there, and being stirred by his enthusiasm into attending Fébur's chemistry lectures along with him. Before that must have taken place his pilgrimage to Descartes, who died in 1650. Apparently Sir Kenelm had gone to Egmont as an unknown stranger; and it throws light on his wide reputation as a man of ideas and a conversationalist, that into his torrent of questions and speculation Descartes broke with, "You can be none other than Digby." The English scientist's practical mind—for he had always a practical end in view, however fantastic his methods—showed itself in his counsel to the author of the Discours sur la Méthode. Why all this labour for mere abstract speculation? Why not apply his genius to the one great subject, the prolongation of human life? Descartes, it appears, did not need the advice. He said the subject was engaging his mind; and though he "dared not look forward to man being rendered immortal, he was quite certain his length of life could be made equal to the patriarch's." In fact, he was composing at the time an Abrégé de Médecine, and popular report said he believed men could live four or five hundred years. He died prematurely of too much faith in his own medical theories.
In 1653 permission was given to Digby to return, on condition he would not meddle with Royalist plots. He had been in communication with Cromwell, and had done some diplomatic business for him in Paris. On his return in 1654, and for the next few years, he was in the closest relations with the Protector, thereby carrying out the principle he had probably adopted from White, of a "universal passive obedience to any species of government that had obtained an establishment." His Royalist friends made an outcry, and so did the Puritans; but Digby was confident of obtaining from Cromwell great advantages for the English Catholics, and the Protector, it seems, fully trusted the intentions and the abilities of this strange and fascinating personality who came to him out of the enemy's camp. Delicate business was given into his hands, that of preventing an alliance between France and Spain. Prynne, in his True and Perfect Narrative, bitterly denounced Cromwell in "that Sir Kenelme Digby was his particular favourite, and lodged at Whitehall; that Maurice Conry, Provincial of the Franciscans in England, and other priests, had his protections under hand and seal." Of Digby's feelings towards Cromwell there is clear evidence. It seems his loyalty had been questioned in his absence; and he writes from Paris, in March, 1656, to Secretary Thurloe: "Whatsoever may be disliked by my Lord Protector and the Council of State must be detested by me. My obligations to his Highness are so great, etc." And again, "How passionate I am for his service and for his honour and interest, even to exposing my life for him." The intimacy, begun on both sides in mere policy, had evidently grown to friendship and mutual admiration.
The illness of which he died had already attacked him, and it was for his health he went to Montpelier in 1658. His stay in that seat of learning was made memorable by his reading to a company of eminent persons his Discourse on the Powder of Sympathy, which has brought him more fame and more ridicule than anything else. I have already referred to the secret confided to him as a youth in Florence by the Carmelite Friar from the East. When he came back to England he spoke of the great discovery, and had occasion to use it. Howell—of the Familiar Letters—was, according to Sir Kenelm's account, wounded while trying to part two friends who were fighting a duel. His wounds were hastily tied up with his garter, and Digby was sent for. Digby asked for the garter-bandage, and steeped it in a basin in which he had dissolved his secret powder (of vitriol). Immediately Howell felt a "pleasing kind of freshnesse, as it were a wet cold napkin did spread over my hand." "Take off all the plasters and wrappings," said Digby. "Keep the wound clean, and neither too hot nor too cold." Afterwards he took the bandage from the water, and hung it before a great fire to dry; whereupon Howell's servant came running to say his master was much worse, and in a burning fever. The bandage plunged once more in the dissolved powder, soothed the patient at a distance; and in a few days the wound was healed. Digby declared that James and Buckingham were interested witnesses of the cure; and the king "drolled with him about it (which he could do with a very good grace)." He said he divulged the secret to the Duke of Mayenne. After the Duke's death his surgeon sold it so that "now there is scarce any country barber but knows it." Why did not Digby try it on his wounded men at Scanderoon? His Discourse to the learned assembly is a curious medley of subtle observation and old wives' tales, set out in sober, orderly, one might almost say scientific, fashion. Roughly, the substance of it may be summed up as "Like to like." The secret powder is a medium whereby the atoms in the bandage are drawn back to their proper place in the body! After Digby's death you could buy the powder at Hartman's shop for sixpence.
At the Restoration he returned to England. He was still Henrietta Maria's Chancellor. His relations with Cromwell had never broken their friendship; and probably he still made possets for her at Somerset House as he had done in the old days. But by Charles II there was no special favour shown him, beyond repayment for his ransom of English slaves during the Scanderoon voyage; and in 1664 he was forbidden the Court. The reason is not definitely known. Charles may have only gradually, but at last grimly, resented, the more he learnt of it, Digby's recognition of the usurper.