TRANSLATOR'S PREFACE
��As indicated in the Author's Preface this English edition of the book differs considerably from the original Belgian edition. Many parts have been expanded, some corrections introduced, and the whole brought up to date.
All the figures have been redrawn for this, edition and one or two extra inserted, and I am indebted to my friend Mr. W. R. Morton for kindly making the drawings for me.
I desire to express my thanks to Mrs. Hurter for per- mitting me to see the part of the translation which her late husband had prepared. v
To my friend and colleague Dr. T. S. Patterson I am indebted for many valuable suggestions during the transla- tion and also for his kind assistance in reading the proofs.
J. McC. February 1899.
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