The design of the Publishers of the Polytechnic Library is to produce a Series of highly-instructive Works, which the Public may be tempted to buy, because they will be cheap,—be induced to read, because they will be brief,—be competent to understand, because they will be clearly written,—and be able to profit by, because they will be WORKS OF PRACTICAL UTILITY. Every volume, therefore, will contain a complete Treatise relating to one of the useful arts or sciences, or the chemical or mechanical trades.