Mr. Charles Green, civil engineer. Captain Henry Scott. Mr. Crawford Campbell, civil engineer. Mr. William Morton, civil engineer. It is not within the author's power to state how far the instruction received was based on practice already then recorded in books, or on modifications introduced by the above gentlemen. There are always plenty of persons ready to declare that there is nothing new under the sun, to depreciate every improvement, and to imagine their own genius augmented by treating matters and persons in a contemptuous style; such persons are not by any means to be envied, and it is not the author's wish to imitate them. A large portion of this book is reprinted from the second edition of the author's Curve-Book, published in 1869, the greater part of which confined itself to the setting-out and designing of curves of railways, canals, and roads; but which also contained an Appendix on Errors in Levelling; the former being chiefly the result of experience on the Metropolitan Railway, the latter being called forth by levelling operations on the Tumbaddra Canal, which had in some parts a fall of only four inches per mile, and required special care and consideration, necessitating reference to the errors recorded in the extended levelling operations of the Great Trigonometrical Survey of India. The additions in this book consist of Part I. On Surveying, and Part IV. On RouteSurveys and minor astronomical observations in connection with them; both of these parts are based on notes, experience, and observations made by the author on land and at sea, with the exception of two examples of longitude-observation at sea worked out by him on data recorded by others. Part I. was recently condensed from notes and written for the use of pupils. Part IV. was condensed in the same way for the use and convenience in reference of the author himself on the occasion of his services being accepted as surveyor to an expedition intending to proceed from India by land route to China under Captain Smyth. This eventually was countermanded at the advice of the British representative at Pekin, who expected a recurrence of the fate of the former expedition (whose officers were tortured and partially burnt alive), and wished to avoid political difficulties of an inconvenient nature. The condensed notes consequently became useless for that particular object, but may yet answer the similar purposes of travellers generally. The observations at sea were subsequently taken and have been since added to this portion of the book. The subjects more specially avoided are, descriptions of instruments generally which are in common use and can be seen, information and tabular matter more specially useful to the designer, and information and models of plans for the draughtsman to follow or imitate; these are subjects distinct from those more specially useful to the surveyor and setter-out. The adjustments of instruments are, however, explained, and the necessary knowledge of the requirements of the draughtsman or designer from the surveyor or setter-out acting in accordance with him is also indicated in occasional remarks. The object of the book is thus extremely limited in one respect, though extensive in another. The Surveys shown in the Plates and Records have been mostly executed by the author at various times; but in some cases, when his note-books did not supply sufficient record of any Survey suited to the special purpose of a book of this sort, the want was supplied by others, whose kindness is therefore here acknowledged with thanks. Among the Route Surveys, the observations at sea were his own, and the Thibetan Routes Record was obtained through the influence of others. The particular portions of the book containing matter for which the author is not indebted to anyone in any way are, the two systems of ranging curves on six-point polygonal methods, the corresponding mode of ranging a compound curve, some of the notes on telemetrical operations, and some of those on errors in levelling, more especially the notice of reflex refractive action in hot climates. In other respects the book is, as proposed, an account of known or of modified methods applicable in practice; it is intended to be useful in occasionally refreshing the memory of those thoroughly conversant with all of them, and in shortening their labour by the tables and formulæ, while it may be of greater use to those whose survey-practice has been. limited to some one or two special branches, or to none. With reference to its use to this latter class of students, it must be frankly confessed that this book was not written with the object of making a Surveyor out of an utterly inexperienced person by its perusal alone. No book can ever do this, or go beyond assisting in doing it. Surveying is practical work of a mechanical description, that is generally acquired by imitating other persons, and by personal practice and experience; it requires but little skill or science, as it merely demands a thorough practical and theoretical knowledge of method, and a competent facility of execution, combined with care and judgment. The knowledge of method may be obtained from a book, if a suitable one can be found, but the facility of execution, the mechanical manipulation of instruments and appliances, and general management in the field would be very tediously acquired by any beginner that entirely dispensed with personal guidance; hence the necessity for following and imitating some experienced person at the onset, and at the same time learning the motives of his procedure. Such a person should evidently neither be a purely practical nor a purely theoretical man; for the former may perform his work automatically, or as a conjurer does his tricks, and leave his pupil to become a mere imitator, a very probable case when the purely practical man either plumes himself on his ignorance of theory, or is unable to explain his motives; on the other hand the purely theoretical man, that has had little or no practice, cannot possibly serve as a model for guidance in actual work in which he is inexperienced; the best guide, and generally also the best Surveyor, is hence a person both thoroughly conversant with all theory bearing on the subject, and also fully competent in practice, whose experience has been gained in several branches of the subject, and whose ideas and habits are free from narrow-minded maxims and traditions; a guide of limited experience should be followed in his special branch only. In learning to survey, as in learning many other things, the first, and also the most important point, is to do it well, the second to do it rapidly; both exactitude and dexterity are inherent individual qualities which may be cultivated to a certain degree, and generally, though not always, to the extent sufficient to make a fairly good Surveyor; a want of precision, resulting in slovenly and useless work is fatal to good surveying, while an amount of exactitude in excess of the requirements of the case, which causes waste of labour, is merely a result of bad judgment, and may be more easily remedied. Rapidity, estimated by the time spent on a survey, is only to a certain extent dependent on individual dexterity or rapid mechanical manipulation; it also depends on the means and methods employed, the general arrangements for work, and on many fortuitous circumstances, such as the possibility of obtaining sufficient men, instruments, appliances, poles, and pegs at the immediate instant and place where they are required, and on the freedom from mistakes and delays of chainmen and subordinates; extreme dexterity is hence not so absolutely necessary in surveying as good management and judgment, while a moderate want of dexterity may be well compensated by the latter qualities combined with a knowledge of expedients: hence accuracy and knowledge may be considered indispensable, and dexterity very advantageous, in survey-practice. |