Petty says that he has "had many flying thoughts, concerning the Advancement of Reall Learning in generall, but particularly of the Education of Youth, Mathematicks, Mechanicks, Physick, and concerning the History of Art and Nature", and he believes that his letter to Hartlib "can please only those few, that are Reall Friends to the Designe of Realities, not those who are tickled only with Rhetoricall Prefaces, Transitions and Epilogues, and charmed with fine Allusions and Metaphors (all of which I do not condemn).

"[22] In the body of the pamphlet, titled 'The Advice for Advancement of some particular Parts of Learning', which has a total of 26 pages, Petty begins with placing himself in the tradition of Francis Bacon ("Lord Verulam").

[23] Adamson splits the "Advice" in four parts:[24] Petty's letter opens with the remark that he has strong sympathies with Hartlib's idea to create an 'Office of Publick addresse' and is willing to donate all the money he gains with his invention of "Double Writing" to this good cause.

[25] In order to fulfill this task, Petty proposes the establishment of "universal schools", 'Ergastula Literaria,' or 'Literary Workhouses,' in which children may be taught to read and write.

But, as Wilson Lloyd Bevan observes in his Sir William Petty: A Study in English Economic Literature of 1894, "in these literary work-houses a child would not only learn reading and writing.

"[26] Petty further proposes that 'the business of education' should not be committed to the worst and unworthiest of men; but that it be seriously studied and practised by the best and ablest persons.

[28] Next Petty suggests the establishment of a 'Gymnasium Mechanicum,' or 'College of Tradesmen for the Advancement of all Mechanicall Arts and Manufactures,' to be such that one at least of every trade (the prime most ingenious workman) might be elected a Fellow, and allowed therein a handsome dwelling rent free.

[30] Within the walls of the Gymnasium there was also to be a 'Nosocomium Academicum,' or model hospital for the benefit of the scientific practitioner, as well as of the patient, and a complete 'Theatrum botanicum', 'stalls and Cages for all strange Beastes and Birds, with Ponds and Conservatories for all exotick Fishes'.

[34] He then proposes compiling a work with the title Vellus Aureum sive Facultatum Lucriferarum discriptio Magna (the Golden Fleece, or great description of the Money-making Faculties), "wherein all the practesed wayes of getting a Subsistance and whereby Men raise their fortunes, may be at large declared.".

The Advice to Hartlib concludes with the expression of a regret that no 'Society of Men' as yet exists 'as careful to advance arts as the Jesuits are to propagate their religion,' and with a suggestion of a work on the lines of Bacon's 'Advancement of Learning,' which should be a treatise on 'Nature free,' or on arts and manufactures relieved of restraint, in contrast with a 'History of Nature vexed and disturbed,' or of trade under the restraints of the then existing commercial system.

[36] The literary work-houses, or 'Ergastula Literaria', which are proposed by Petty in his Advice to Hartlib have become a symbol for the spirit of educational renewal in the seventeenth century.

Bevan, Wilson Lloyd, in his Sir William Petty: A Study in English Economic Literature (1894)[39] gives a rather extensive description of the Advice to Hartlib, naming it "the Tractate on Education".

Anderson gives much attention to the "universal schools" that Petty wanted to establish, the "Ergastula Literaria", "a phrase which is meant to cover a whole theory of Education, and that a revolutionary one."

[37] According to Knox, H. M., professor of Education at Queen's University Belfast, who wrote an essay about The Advice to Hartlib in 1953[43] the work was difficult to find for a long period, until it was republished in 1876, and again in 1946.

Knox starts his essay with the following statement: "To few it is given to write an enduring treatise on education at the age of twenty-four (he means: twenty-seven), but few possess the versatile genius of Sir William Petty.

"[44] Knox also makes a comparison with the tractate Of Education of John Milton, published 1644, and thinks that the Advice to Hartlib is "full of original matter worthy of detailed study".