Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

PREFACE TO THE SEVENTH EDITION. The- favourable reception of the ‘ Pocket- Book,’ testified in the sale of Six Editions in little more than a year alter its first appearance, increases the author’s obligations to render it to the utmost of his ability more worthy of such public approbation. Though fuljy alive to these obligations, his power of fulfilling them lias been necessarily limited by the superintendence of a very arduous work in a distant colony. But he has had the good fortune to receive, and now has the pleasure to acknowledge, valuable assistance from scientific and professional persons who have taken an interest in the work. Ihougii of these many are entirely unknown to him, he