Physician as he was, Petty did not put his faith in “medicaments”—witness his savings in the Army drug department. “There is a conceit current in the world,” he told Robert Boyle, “that a medicament may be physic and physician alike.” What a mistake! “Recommendations of medicaments do not make them useful, but do only incite me to make them so by endeavouring experimentally to find out the virtues and application of them.” And it is a hard matter to discover their true virtues. “As I weep to consider,” says Petty, “so I dread to use them, without my utmost endeavour first employed to that purpose.” It is a manly, outspoken letter, though it may have seemed a little caustic at the time. And it had its effect. Robert Boyle came back to Dublin to work, under Petty’s direction, at anatomical dissection—and possibly to read less. He was still ailing, still dejected, still longing to be back in London; but, “that I may not live wholly useless,” he wrote to Mr. Clodius, Hartlib’s doctor son-in-law in London, “or altogether a stranger in the study of Nature, since I want glasses and furnaces to make a chemical analysis of inanimate bodies, I am exercising myself in making anatomical dissections of living animals, wherein (being assisted by your father-in-law’s ingenious friend, Dr. Petty (our General’s Physician)) I have satisfied myself of the circulation of the blood and the (freshly discovered and hardly discoverable) _receptaculi chyli_, made by the confluence of the _venæ lacteæ_, and have seen (especially in the dissections of fishes) more of the variety and contrivances of Nature and the majesty and wisdom of her Author than all the books I ever read in my life could give me convincing notions of.” While he is kept a prisoner in Ireland, he says, he will be delighted if there is anything he can do to help Clodius in an anatomical way; if there is anything “wherein my knives may give you any satisfaction, I shall be very proud to employ them to so elevated an end.” Meantime he was doing as Clodius had asked him—looking into the “mineral advantages of Ireland.” But “in this illiterate country, I find all men so perfect strangers to matters of that nature, that my inquiries have been as fruitless as diligent.” He can hear nothing about antimony mines; “but for iron I may be able to give you a good account of it, and to bring you over of the ore, my eldest brother having upon his land an iron-work that now yields him a good revenue, and I having upon my own land an iron-mine, to which, before the wars, belonged a (since ruined) work, which I have thoughts of resetting up. I am likewise told (but how truly I know not yet) of a little silver-mine lying in some land of mine; and very lately in a place which belongs to a brother of mine they have found silver ore very rich, for, being tried, it is estimated (as he tells me that means to deal for it) at between thirty and forty pounds a ton; but whether or no this be