The fundamental requisites for a really good textbook in any applied subject, or for a really good reference book for self-instruction, are: first, that it shall contain all of the more important facts and principles required by its readers; and second, that this information and theory shall be presented clearly and forcibly, unclouded by a mass of irrelevant matter. The strength of this short text lies in the satisfac tory manner in which it meets both of these conditions. It is a book which supplies the underlying reasons, the whys of his task, which constantly present themselves to the intelligent man on the job.