"The bulk of the material presented [in this book] is the common heritage of the profession, and if any may think there is insufficient reference to previous writers, let him endeavor to find to whom the origin of our methods should be credited. The science has grown by small contributions of experience since, or before, those unnamed Egyptian engineers, whose works prove their knowledge of many fundamentals of mine engineering six thousand eight hundred years ago. If I have contributed one sentence to the accumulated knowledge of a thousand generations of engineers or have thrown one new ray of light on the work, I shall have done my share." In the latter chapters of the book Hoover, having devoted the earlier chapters to technical methods, treats of the administrative and financial phases of mining. The last chapter is devoted to the "character, training, and obligations of the mining engineering profession" in which he sets up a standard of professional ethics for the engineer of the very highest degree and reveals clearly his own genuinely philanthropic attitude toward his fellow men. In the discussion of mining administration there is a concise but illuminating treatment of the subject of labor unions. After discussing contract work and bonus systems he says: "There is another phase of the labor question which must be considered, and that is the general relations of employer and employed. As corporations have grown, so likewise have the labor unions. In general, they are normal and proper antidotes for unlimited capitalistic organization.