stretched straight by a light bow of whalebone. In practical hands, this method is sufficiently accurate in most cases. The student will do well to try it on figures, the content of which he has previously ascertained by perfectly accurate methods. Sometimes this method may be advantageously combined with the preceding; short lengths of the croooked boundary being "Equalized," and the fewer resulting zigzags reduced to one line by the method of Art. (78), &c. CHAPTER IV. SURVEYING BY THE PRECEDING METHODS COMBINED. 125) All the methods which have been explained in the three preceding chapters-Surveying by Diagonals, by Tie-lines, and by Perpendiculars, particularly in the form of offsets-are frequently required in the same survey. The method by Diagonals should be the leading one; in some parts of the survey, obstacles to the measurement of diagonals may require the use of Tie-lines; and if the fences are crooked, straight lines are to be measured near them, and their crooks determined by Offsets. (126) Offsets are necessary additions to almost every other method of surveying. In the smallest field, surveyed by diagonals, unless all the fences are perfectly straight lines, their bends must be determined by offsets. The plat (scale of 1 chain to 1 inch), and field-notes, of such a case are given below. A sufficient num ber of the sides, diagonals, and proof-lines, to prove the work, should be platted before platting the offsets. (127) Field-books. The difficulty and the importance of keeping the Field-notes clearly and distinctly, increase with each new combination of methods. For this reason, three different methods of keeping the Field-notes of the same survey will now be given, (from Bourns' Surveying), and a careful comparison by the student of the corresponding portions of each will be very profitable to him. |