Scientific Text-Books. 165 has unravelled fresh threads of the tangled skein of hidden truth. Promptly the first edition becomes "out of date," and our author must needs re-furbish his literary weapons, and do battle with some fresh competitor, ever ready to spring up, by bringing out a second edition, containing all facts up to date. The first edition is no longer asked for, but is relegated to some out of the way shelf at the top of the book case, while its value in the market often falls to half the original cost. Thus, exactly the converse happens to what obtains in the literary world of poetry and fiction, where first editions in a few years become worth double or treble what they originally cost. Such is the general rule with regard to works of science. A constant succession of editions is turned out year after year, and newer and newer becomes the dress of the old friend till its earliest attire is at length well nigh unrecognisable. But no rule is without its exceptions. There are certain branches of science, the original editions, or perhaps the only edition, of works on which are of permanent value, or the latest edition published years ago is still looked up to and consulted. Especially is this noticeable in those departments less abstruse. To take a few instances at random : works on the geology of particular areas such as the British Isles, because we know that what was written twenty or thirty years ago on that subject has proved true, though many additional facts have been brought to light. Or, again, works on human and comparative osteology, which is one of the most demonstrable branches of science ; also systematic treatises or those relating to the classification of plants or animals, for these old systems are nothing less than frameworks which have never been broken up or destroyed. Repairs, alterations and additions there may have been in the way of transferring one species to another order, or adding freshly-discovered species to different orders, or creating varieties out of a species whose characters are not very constant ; but as to the task of re-naming the whole vegetable and animal king- dom, why, nobody dreams of it : hence old works on such subjects have become standard. A few examples of such works are here quoted : Darwin's Origin of Species (1859). Descent of Man (1871). Owen (Richard) Odontographia, or Treatise on the Compara- tive Anatomy of Teeth (1845). On the Anatomy of Vertebrates. Lyell (C.) Principles of Geology.
