in principle, for books require a low temperature rather than a high one, and great damage will be done to the bindings if the pipes are placed so near to them. In a case 7 feet 6 inches high it will be seen that with a base of 2 inches, and a top of 1 inch, there is left a space available for books of 87 inches. This will take eight shelves for ordinary octavo books, 10 inches in height, or ten rows of crown octavo books, 7½ inches in height, allowing ¾ of an inch for the thickness of each shelf. If mixed sizes are wanted, each division will take five shelves for crown octavo, and four shelves for ordinary octavos; and if a few shelves for larger books are required, they may be obtained by dividing the space into two shelves of 8 inches, five shelves of 10 inches, and one of 14; but generally the taller books will be best shelved away from the smaller, as they are broader, and will require deeper shelves. The depth of shelf required for the ordinary octavos, whose height we have been considering, will be from 5½ to 7½ inches, so a shelf 8 inches in depth will be found to be sufficient. To recapitulate, we may safely say that 75 per cent, of the books in ordinary libraries can be placed upon shelves varying from 8 to 10 inches in height and 8 inches in depth.
It is important that all shelves in the library be the same length, so that when it is necessary to remove part of any class to another place, the books may still keep their relative positions to each other. Another advantage is, that any spare shelf will fit any place where it may be wanted,
