Averages are very uncertain standards of comparison, as a single book rarity often costs more than a hundred volumes of the new books of the day; but in a library filled with the best editions of classical and scientific works, and reference books, I presume that two dollars a volume is not too high an estimate of average cost, in these days represented by the last twenty years. For a circulating library, on the other hand, composed chiefly of what the public most seek to read, half that average would perhaps express the full commercial value of the collection. Of its intrinsic value I will not here pause to speak. There are many methods of book buying, of which we may indicate the principal as follows: 1. By direct orders from book dealers. 2. By competition on select lists of wants. 3. By order from priced catalogues. 4. By purchase at auction sales. 5. By personal research among book stocks. 6. By lists and samples of books sent on approval. Each of these methods has its advantages--and, I may add, its disadvantages likewise. The collector who combines them, as opportunity presents, is most likely to make his funds go the farthest, and to enrich his collection the most. Direct orders for purchase are necessary for most new books wanted, except in the case of the one government library, which in most countries, receives them under copyright provision. An advantageous arrangement can usually be made with one or more book-dealers, to supply all new books at a fairly liberal discount from retail prices. And it is wise management to distribute purchases where good terms are made, as thereby the trade will feel an interest in the library, and a mutuality of interest will secure more opportunities and better bargains. The submission of lists of books wanted, to houses having large stocks or good facilities, helps to make funds go as far as possible through competition. By the typewriter such lists can now be manifolded much more cheaply than they can be written or printed. Selection from priced catalogues presents a constantly recurring opportunity of buying volumes of the greatest consequence, to fill gaps in any collection, and often at surprisingly low prices. Much as book values have been enhanced of late years, there are yet catalogues issued by American, English and continental dealers which quote books both of the standard and secondary class at very cheap rates. Even now English books are sold by the Mudie and the W. H. Smith lending libraries in London, after a very few months, at one-half to one-fourth their original publishing price. These must usually be rebound, but by instructing your agent to select copies which are clean within, all the soil of the edges will disappear with the light trimming of the binder.