Select Specimens of Natural History Collected in Travels to Discover the Source of the Nile. Volume 5.

As it has been my endeavour, throughout this history, to leave nothing unexplained that may assist the reader in understanding the different subjects that have been treated in the course of it, I think myself obliged to say a few words concerning the manner of arranging this Appendix. With regard to the Natural History, it must occur to every one, that, however numerous and respectable they may be who have dedicated themselves entirely to this study, they bear but a very small proportion to those who, for amusement or instruction, seek the miscellaneous and general occurrences of life that ordinarily compose a series of travels.
By presenting the two subjects promiscuously, I was apprehensive of incommoding and disgusting both species of readers. Every body that has read Tournefort, and some other authors of merit of that kind, must be sensible how unpleasant it is to have a very rapid, well-told, interesting narrative, concerning the arts, government, or ruins of Corinth, Athens, or Ephesus, interrupted by the appearance of a nettle or daffodil, from some particularity which they may possess, curious and important in the eye of a botanist, but invisible and indifferent to an ordinary beholder.
To prevent this, I have placed what belongs to Natural History in one volume or appendix, and in so doing I hope to meet the approbation of my scientific botanical readers, by laying the different subjects all together before them, without subjecting them to the trouble of turning over different books to get at any one of them. The figures, landscapes, and a few other plates of this kind, are illustrations of what immediately passes in the page; these descriptions seldom occupy more than a few lines, and therefore such plates cannot be more ornamentally or usefully placed than opposite to the page which treats of them.
Some further consideration was necessary in placing the maps, and the Appendix appeared to me to be by far the most proper part for them. The maps, whether such as are general of the country, or those adapted to serve particular itineraries, should always be laid open before the reader, till he has made himself perfectly master of the bearings and distances of the principal rivers, mountains, or provinces where the scene of action is then laid. Maps that fold lie generally but one way, and are mostly of strong paper, so that when they are doubled by an inattentive hand, contrary to the original fold they got at binding, they break, and come asunder in quarters and square pieces, the map is destroyed, and the book ever after incomplete; whereas, even if this misfortune happens to a map placed in the Appendix, it may either be taken out and joined anew, or replaced at very little expence by a fresh map from the bookseller.