PREFACE THE author hopes that this book will help to fill a small gap in the literature of surveying. There is, unless he is mistaken, no general treatise on tacheometry in which both the practical side of the subject and methods of measurement other than the stadia method are given adequate treatment. The main object of the book is to encourage young surveyors, particularly those in undeveloped countries, to take a greater interest in tacheometry, and especially in that branch of it known as stadia measurement. Surveyors on the whole are inclined to fight shy of ordinary tacheometry. This is largely due to the fact that in text- books on surveying the treatment of the subject is not as practical as it might be. To take one example almost every text-book mentions only one method of reading the staff, namely that in which all three hairs are read to two decimal places in order to provide a check on the accuracy of the readings. This, by itself, is responsible for discouraging many a beginner. To the surveyor who cannot afford an assistant to book his readings for him this conventional method of reading the staff is too tedious for words. In this book special attention has been given to the practical side of the subject. In Chapter VI, on Field Work, every effort has been made to instruct the beginner in the art of conducting operations in the field. The methods there recommended are based on long and varied experiences the author has both practised and taught tacheometry for a great many years. With regard to Chapter XI on Special Instruments, the author is aware that it is impossible, in the few pages allotted to the subject, to do it justice. His intention has been merely to give the reader some idea of what has been attempted or achieved in this particular field. There are one or two minor controversial points to which the author may, perhaps, be allowed to refer briefly. The first is the use of the words tacheometer and anallactic instead of tachymeter and anallatic. Although he is in sympathy with those who would like to see the older and more correct form tachymeter reinstated, he is convinced that it is too late now to make the change. So far as British surveyors are concerned tacheometer and tacheonzetry have come to stay. As regards anallatic-a foreign word, to be found in many text-books but in none of the dictionaries-since it is clearly intended to be the antonym of parallactic the correct English spelling would appear to be anallactic. Secondly, it may be objected that horizontal-base subtense measurement is, strictly speaking, not a form of tacheometry. This may possibly be so but as vertical-base subtense is beyond doubt a branch of tacheometry and it is customary in text-books to include subtense measurement in the chapter on Tacheometry, there is, it would seem, ample justification for including it here. In fact, to exclude the subject from these pages would probably be the greater offence of the two. Lastly, the authors insistence on the need for flexibility in stadia observations may be regarded as an obsession but he is sure that any surveyor who has learnt his tacheometry in a hard school will agree with him on this point. The author wishes to express his warm sense of gratitude to all those who have so kindly helped him to produce this work. To his staunch friend and former assistant Mr. Y. L. Pao, B.Sc., he is indebted more than he can say. Mr. Pao not only took a keen and practical interest in the preparation of this book, but after Hong Kong fell in December 1941, he managed with the aid of his colleague, Mr. N. P. Koh, M.Sc...