In September, 1858, Darwin, at the earnest advice of Lyell and Hooker, set to work to prepare a volume on the transmutation of species. The book cost him more than thirteen months' hard labor. It was published in November, 1859, under the title of "Origin of Species." This, which Darwin justly regarded as the chief work of his life, was from the first highly successful. The first edition was sold on the day of publication, and the book was presently translated into almost every European tongue. Darwin himself attributed the success of the "Origin" in large part to his having previously written two condensed sketches, and to his having finally made an abstract of a much larger manuscript, which itself was an abstract. By this winnowing process he had been enabled to select the more striking facts and conclusions. As to the current assertion that the "Origin" succeeded because the subject was in the air, or because men's minds were prepared for it, Darwin was disposed to doubt whether this was strictly true. In previous years he had occasionally sounded not a few naturalists, and had never come across a single one who seemed to doubt about the permanence of species. Probably men's minds were prepared in this sense, that innumerable well-verified facts were stored away in the memories of naturalists, ready to take their proper places as soon as any theory which would account for them should be strongly supported. Darwin himself thought that he gained much by a delay in publishing, from about 1839, when the "Darwinian" theory was clearly conceived, to 1859; and that he lost nothing, because he cared very little whether men attributed most originality to him or to Wallace. Darwin's "Variation of Animals and Plants under Domestication" was begun in 1860, but was not published till 1868. The book was a big one, and cost him four years and two months' hard labor. It gives in the first volume all his personal observations, and an immense number of facts, collected from various sources, about domestic productions, animal and vegetable. In the second volume the causes and laws of variation, inheritance, etc., are discussed. Towards the end of the work is propounded the hypothesis of Pangenesis, which has been generally rejected, and which the author himself looked upon as unverified, although by it a remarkable number of isolated facts could be connected together and rendered intelligible.