In April, 1828, Swainson published an eulogistic account of some of Audubon's plates, and shortly after they became good friends, as their familiar letters already reproduced amply testify;[88] in the autumn of that year, as we have related, they visited Paris together, and they kept up a correspondence for a number of years. At this time Swainson was known as a systematic zoölogist of merit and an excellent draughtsman, having published a series of "Zoölogical Illustrations" that seem to have been well received. Moreover, as early as 1824, he had adopted the notorious "Circular System" of the classification of animals, and at this time was its most zealous advocate in England. The tenets of this curious doctrine, often called "Quinarianism" from the recurrence of the number _5_, was confused in a mystical jargon which conveys little meaning to a reader of today; it was derived from William Sharp MacLeay, who had advocated a similar system in his _Horae Entomologicae_, published in 1821. According to Swainson's creed, "all things that have life have been created upon one plan, and this plan is founded on the principle of a series of affinities returning into themselves; which can only be represented by a circle." "This sublime discovery," which, as Swainson thought, was sufficient "to immortalize a name," was duly attributed to his "illustrious countryman."[89] In the summer of 1830, when Audubon was ready to prepare the letterpress of his mammoth plates and needed assistance in its technical details, he applied to his friend Swainson, who, as we have seen, was then living at a farmstead in the Hertfordshire country, not far from St. Albans.[90] Some of the letters which passed between the two naturalists after the return of the former to England, in the spring of that year, will now be given, without amelioration or change of any sort. It should be remembered that Swainson at this time was in an overwrought state, since he was dependent mainly upon his scientific writings for the support of a family of five children, oppressed by pecuniary difficulties, and, no doubt, irritated by lack of success and the rebuffs which a leading part in the Quinarian movement was certain to entail. Audubon's letter[91] which follows served to answer that of Swainson, bearing date of January 30, 1830,[92] had been received in America but too late for the fulfillment of its commissions. References to Audubon's "book," which unfortunately proved a stumbling block in the path of friendship, are noticed here and in Swainson's reply for the first time. _Audubon to William Swainson_ LONDON, _May 5th 1830_. MY DEAR MR. SWAINSON,