It was Professor Henslow who secured for young Darwin the appointment of naturalist to the voyage of the "Beagle." This voyage lasted from Dec. 27, 1831, to Oct. 2, 1836. The incidents of this voyage will be found set forth in Darwin's "Public Journeys." The observations made by him in geology, natural history, and botany gave him a place of considerable distinction among scientific men. In 1844 he published a series of observations on the volcanic islands visited during the voyage of the "Beagle," and two years later "Geological Observations on South America." These two books, together with a volume entitled "Coral Reefs," required four and a half years' steady work. In October, 1846, he began the studies embodied in "Cirripedia" (barnacles). The outcome of these studies was published in two thick volumes. The time came when Darwin doubted whether the work was worth the consumption of the time employed, but probably it proved of use to him when he had to discuss in the "Origin of Species" the principles of a natural classification. From September, 1854, and during the four ensuing years, Darwin devoted himself to observing and experimenting in relation to the transmutation of species, and in arranging a huge pile of notes upon the subject. As early as October, 1838, it had occurred to him as probable, or at least possible, that amid the struggle for existence which everywhere goes on in the animal world, favorable variations would tend to be preserved, and unfavorable ones to be destroyed. The result would be the formation of new species.