In this First Edition, entirely from manuscript, there will no doubt be errors and omissions; therefore the author will feel obliged by the receipt of any notes that he may make use of for future corrections, should another Edition be demanded.
W. F. S.
Great Turnstile, 1890.
PREFACE TO THIRD EDITION.
The note at the end of the First Edition of this work referred to on the preceding page has brought the author many letters from professional men, who have kindly taken interest in the work by offering suggestions which are now incorporated as far as practical in this Edition, and for which thanks are tendered.
One important improvement of late years in the construction of surveying instruments is due to the greater perfection of modern machinery, and the adoption of special machines to shape out many parts of the work from the solid which were formerly screwed together in many pieces, which made the instruments heavier and also liable to become loose in parts by jars, so as to cause the necessity of frequent readjustments.
Another important improvement in modern surveying instruments is in their lightness, due to the discovery of permanent aluminium alloys, by which many parts of instruments that are shaped out in the solid may be reduced to one-third the weight of the gun-metal castings formerly used entirely for these parts.