Wilkins was a diligent student, and wrote books of many kinds. These books the writer does not pretend to have read, save in the most hurried, even careless way, except two of them, the 'Real Character' and 'Natural Religion.' The others are of interest to natural philosophers, as containing anticipations of discoveries and ideas which belong to a later age, and as showing that Wilkins possessed the inspiring conviction of all genuine men of Science, that for it the word impossible does not exist.

In 1638 he published his first work, an Astronomical treatise, the fruit of his studies at Oxford and at Fawsley. It is entitled 'The Discovery of a World in the Moone, or a discourse tending to prove that there may be another habitable World in that Planet': in the third impression, issued in 1640, is added a "Discourse concerning the Possibility of a Passage thither." Like Lucian he imagined a voyage to the moon, though he admits that the journey through the air was a formidable difficulty. He successfully defended his views against an objection raised by the Duchess of Newcastle. That clever and eccentric lady, the authoress of many "fancies," philosophical and poetical, asked him where she was to bait her horses if she undertook the journey. "Your Grace could not do better," he replied, "than stop at one of your castles in the air." In his treatment of the difficulties caused by the apparent conflict between certain passages of Scripture and the conclusions of Astronomical Science, which he accepts, he anticipates in a remarkable way that explanation of them which rests on the understanding of the meaning of the Bible and of the nature of inspiration. The book was parodied in the story of 'Peter Wilkins' Journey to the Moon,' which even usually well-informed persons have been known to attribute as a jeu-d'esprit to the Warden of Wadham. It was written by Robert Paltock, and published in 1751.

His next production was 'Mercurie; or the Secret and Swift Messenger,'—a treatise on Cryptography or ciphers; curious contrivances whereby A can communicate with C without B's suspecting or understanding, by signs, gestures, parables, and transpositions of the alphabet: such as the writer looked at seemed to confirm the view that every cipher which depends on system, and not on an arrangement of a capricious kind, can be interpreted by an expert, a title to which he lays no claim. The book was meant perhaps for use in the Civil War, as was the system of Wilkins' friend, Dr Wallis, who could both invent and solve such puzzles, and distinguished himself by deciphering the letters of the king which fell into the hands of the Parliamentarians at Naseby. There is also among the "Tracts of Bishop Wilkins," a treatise dated 1648, entitled 'Mathematical Magic; or, the Wonders worked by Mechanical Powers and Motions,' subdivided, according to that distinction, into two books, styled Archimedes and Dædalus. The names are quaint, and the classical illustrations are very numerous. The work is a kind of handbook for engineers, enlivened by quotations, not always apposite, from ancient authors, as was the fashion when high literary culture and science could be more easily combined than in our days of ruthless specialism. It is dedicated in very courtly language to the Prince Elector Palatine. Wilkins looks forward to the Prince's restoration to his dominions—a curious aspiration to be professed by a man who did not, then at least, put his trust in princes. But he did not foresee what was to come, both to himself or others.

His two books of a devotional character were, one on 'The Gift of Prayer,' a formal and elaborate treatise with many divisions and subdivisions, in spirit earnest and devout. Its companion treatise, 'Ecclesiastes; or the Gift of Preaching,' shows a high conception of the learning which he thought necessary for one who would preach well; knowledge of commentators; of preachers, especially of English sermon-writers; of works on Christian doctrine, on the history of Christianity; of all subjects which can be included in Theology. The list of books recommended is enormous, and beyond the reach of any man—even of Wilkins or Casaubon: it must have been intended to be a work of reference, a catalogue from which a student might select. It, like his 'Sermons Preached on Several Occasions,' is illumined by quaint utterances, humorous, sensible, and devout; qualities more frequently combined in those days than in our own, when the "dignity of the pulpit," a lamentable superstition, has weakened its influence, and has made religion appear to simple people remote from common life.

Wilkins' most original and valuable contribution to Theology is 'The Principles and Duties of Natural Religion,' written in his later years, and published after his death by Tillotson. Mr Sanders, the writer of the too short article on Wilkins in the 'Dictionary of National Biography,' says that "in this work there are thoughts which anticipate the argument of Butler's 'Analogy.'" Wilkins, like Butler and Newman, draws distinctions between different kinds of evidence and different degrees of consequent assent. He points out that neither Natural Religion nor Christianity can be proved true by demonstration like a conclusion in geometry, or in any kind of mathematical reasoning; that in default of this inference from self-evident premises to propositions of equal cogency, we must, in a matter of paramount practical importance, be content to judge, as fairly and soberly as we can, by that "probability" which Butler calls "the guide of life." Wilkins perceived, what few in his time perceived, that there are no "demonstrations" of Christianity, nor even of Theism; that faith is faith. Further, he emphasises the harmony between Natural and Revealed Religion, the fact that one is the complement of the other. But in him there are not the depth, candour, and seriousness of Butler, nor that sense of mystery which makes him the weightiest of Christian Apologists in the estimation both of disciples and opponents.

The book by which Wilkins will always be remembered among curious students and philologers is his 'Essay towards a Real Character and a Philosophical Language.' It is a quarto of 600 pages, including an alphabetical dictionary of English words, with their equivalents in what may be called, without irreverence, Wilkinese. It was written at the request of the Royal Society, and, by its order, published in 1688. The meaning of the somewhat obscure title is explained by Wilkins in a very interesting preface. Character means language, or rather writing, and a universal character is the script of a language like that which was spoken before the confusion of tongues; a language for and of all men. By "Real" is signified that the new language is founded on a study of things which are "better than words"; of "the nature of things, and that common notion of them wherein mankind does agree." The making of such a language "will prove the shortest and plainest way for the attainment of real knowledge," and the language thus made will be truly philosophical, or, to use our modern term, scientific. The labour bestowed by Wilkins on his magnificent project was immense, but the result was failure. "Sunt lacrimæ rerum," and tears were never shed over a greater waste of ingenuity and heroic toil, if indeed a fine example of fruitless devotion is to be called waste. With apologies to the Esperantists, it must be said that the invention of a universal language, of any but the narrowest compass, seems impossible, for language, in any real sense, is not made but grows. It is dangerous, however, to dogmatise on possibilities. Misled, as we can gather from his preface, by the proved usefulness of mathematical signs, Wilkins attempted to provide for philosophers of all countries a better means of communication than Latin, then the universal language of literature and science, but in his opinion unscientific, full of anomalies and difficult to acquire; for in it there were, he said, thirty thousand words. In his language there were only three thousand, and they could be learnt by a man of good capacity in a month. His estimate of capacity and diligence is somewhat high. It is possible to explain the principles on which he constructed his new tongue. He began by dividing the universe, the sum total of existence, things, thoughts, relations, after the manner of Aristotle, though not into ten, but into forty categories, or genera, or great classes, such as World, Element, Animal, and apparently species of animals, such as Bird, Fish, Beast: for each of these great classes he devised a monosyllabic name—e.g., De for Element, Za for Fish; each of these genera is subdivided into species indicated by the addition of a consonant, and these are again subdivided into subordinate species distinguished by a vowel affixed. For example—De means an Element, any of the four, Fire, Air, Earth, Water; add to it B, which, as the first consonant, stands for the first species of a genus, and you will have the significant word DEB, which means Fire, for it, we know not why, is the first of the four Elements. Let us take a more complex instance—his name for Salmon. The salmon is a species of Za or Fish, a particular kind of fish called N, namely, the Squameous river fish. This class ZaN is subdivided into lower classes, and the lower class Salmon is called A, which means the red-fleshed kind of squameous river fish, and so a salmon is a ZaNA. If you wished to state the fact that a salmon swims, you would use the words ZaNA GoF, for Go stands for the great category of motion, F for the particular kind of motion meant, swimming. Voice, tense, and mood are indicated by lines of different lengths, straight or curved, crossed, hooked, looped; adverbs and conjunctions by dots or points differently arranged.

Wilkins' universal character therefore means a kind of shorthand writing of his Real Language.

The writer fears that he may only have confused his readers and himself by his bold but poor attempt to express in a few lines the meaning of six hundred pages. He would be the last to ridicule the "folly" of a great man, whose system he has made no very laborious effort to understand, for it seems to be built on sand, on a classification of things superficial, imperfect, and capricious, which would not have been accepted by learned men, and if accepted would have become obsolete in a quarter of a century. The syllable Co stands for all relations between human beings, and these relations are of eight kinds. What would a professor of social science now say to this? What would an ichthyologist say to Wilkins' definition of a salmon? The interest of the book lies in its being the most striking of many proofs of the wide intellectual interests, the alert and insatiable curiosity, and the extraordinary industry of its writer. It has also the pathetic interest of "love's labour lost," for who now reads the 'Real Character,' or who read it twenty years after Wilkins' death? His name was "writ in water," for he spent himself on many things, and did little because he did too much.

The "greatest curioso" of his time relieved his toils by music. Nowhere are Wood's vanity and self-consciousness shown more vividly than in his account of a musical entertainment given by Wilkins in honour of Thomas Baltzar, "the most famous artist for the violin which the world had yet produced. The books and instruments were carried thither," to the Warden's lodgings, "but none could be persuaded there to play against him in consort on the violin. At length the company, perceiving A. W. standing behind in a corner neare the dore, they haled him in among them, and play forsooth he must against him: whereupon, he being not able to avoid it, took up a violin, and behaved himself as poor Troylus did against Achilles." Wood consoled himself for his failure by the honour he acquired from being asked to play with the Master, of whom he maliciously remarks that "he was given to excessive drinking,"—a characteristic comment.

Wilkins' greatest achievement was the founding of the Royal Society. He may be called its founder, if that high title can be given to any one of the eminent men who, in Oxford and in London, revived or regenerated the study of natural philosophy. Pope, Aubrey, and Sprat differ from Wallis in their accounts of the origin of the mother of scientific parliaments. The first three find that origin in meetings held in Wadham College under the presidency of Wilkins. Wallis traces the beginnings of the Royal Society to meetings held in London in 1645. "In that year," he writes, "there had sprung up an association of certain worthy persons inquisitive in Natural Philosophy, who met together, first in London, for the investigation of what was called the new or experimental philosophy, and afterwards several of the more influential of the members, about 1648 or 1649, finding London too much distracted by civil commotions, commenced holding their meetings in Oxford." Among those who removed to Oxford were, "first, Dr Wilkins, then I, and soon after Dr Goddard, whereupon our company divided. Those at London (and we when we had occasion to be there) met as before. Those of us at Oxford, with Dr Ward, Dr Petty, and many others of the most inquisitive persons in Oxford, met weekly for some years at Dr Petty's lodgings, on the like account, to wit, so long as Dr Petty continued in Oxford, and for some while after, because of the conveniences we had there (being the house of an apothecary) to view and make use of drugs, and other like matters as there was occasion. We did afterwards (Dr Petty being gone to Ireland and our numbers growing less) remove thence, and (some years before his Majesty's return) did meet at Dr Wilkin's lodgings in Wadham College."