that "a good surveyor will practise the judging of distance, and will often test his ordinary paces when walking, so that he can obtain the length of a line pretty accurately without the aid of a tape or chain. It often happens that he has to cross forbidden ground over which he cannot chain a line, and this plan will be found most useful. I was once thus stepping the distance across a large field, the property of an irascible farmer, and had proceeded nearly two-thirds of the way when he confronted me with a big stick, saying, 'Hi, you. What business have you on my property? You're a spoiling of these turmits.' 'My good friend, I am doing no harm.' 'I'm no friend of yours; I am your henemy. Come, get out of this, can't yer?' 'Well, then, my good enemy, you see I have already got two-thirds of the way across this field, and it will do the turmits, as you call them, less damage if I go off them in this direction.' 'Wall, may be, it wull; but I'll see you safe off afore I goes away.' 'Thank you. Good afternoon. 196, 197, 198,' and so on until the line was complete. Sometimes, however, an opposing landowner knows what he is about much better than this simple farmer, and puts the surveyor to considerable inconvenience. Imagine the disgusting case of a friend of mine, who in taking a line of levels was constantly confronted by a couple of rustics holding up a large piece of rick-cloth stretched between two poles. Who could object? They were at liberty to stand where they liked, and hold what they liked, and the old farmer stood by and chuckled derisively At length, with a bow, the surveyor retired. The next morning the farmer and he met again some distance ahead. 6 Ah, old fellah!' said Hodge, 'I did yer last night. I know a thing or two.' 'Yes,' quietly remarked my friend, 'but you don't know everything. I was back after dark and completed my line of levels with the aid of a lantern.' It is not an easy thing to take levels with the aid of an artificial light, but it may be done, and it is useful to know that, with a little care, it can be effected."

CHAPTER XVII.

CONTOURS.

A CONTOUR plan enables the surveyor to judge the undulatory nature of any ground, and in setting out work to run lines approximately of equal level or of uniform gradient. (See pages 194, 195.)

They are plotted upon a plan by lines representing the imaginary intersection of horizontal planes with the surface of uneven ground, and form the outline of a horizontal section or the outline of any portion of the hill made by still water rising to that height. The figures written upon the chain dotted lines in the accompanying plan, represent vertical intervals of five feet. The plan is prepared in the following manner. Suppose the altitude of the contour required to be 120 ft. above a given datum (see page 177), and that the nearest reliable bench mark is known to be at a level of 137.86 ft. above the same datum, there is a difference of 17.86 ft. between the level of the bench mark and the required contour. The instrument is set up in a convenient position and adjusted, and if, for example, the staff reads 261, this is booked as a back sight and shows the line of collimation to be at a level of (2·61 plus 137·86) 140:47 ft. above the given datum. Now the contour being 20:47 ft. below this, it is evident that the line of collimation must be lowered in position before a level staff, 14 ft. or 16 ft. long, could be read by the instrument when set up level. A fore sight for the purpose of connecting the levels is taken in such a position that the staff is read near the top, say at 12.85, and the level is re-set in a new position to read near the foot of the staff, say 183. Reducing the book we find the level of the point upon which we changed the level of the line of collimation to be 12762. The position of this point is not recorded in the level book, as it is not required

to be indicated upon the plan, but we have by this means fallen from a known level of 137.86 to a known level of 12762, and have now only to fall 7.62 ft. lower to find the position of a point upon the required contour. Adding 7.62 to 183 we obtain 9:45 as the necessary reading upon the staff to give the height required, and this figure is then booked for reference in the intermediate column. If the staff reads less than 9:40 the staffman is told to go to lower ground, whereas if the staff reads more than 9:50, the staffman is told to come to higher ground. Except where extreme precision is required, the divisions indicating hundreds may be disregarded in reading the staff, but it is well to observe them in the Level Book for sake of accuracy in connecting the levels. So far as points of equal level are concerned, a reflecting level would serve to fix them approximately, but the most accurate work is secured by the aid of a Dumpy level as above described. Signals will have to be agreed upon by which the surveyor can communicate with the staffman when they are too far apart to be within hearing of one another. The position of the contour points in the field is fixed during the process of levelling by stout laths pointed at the ends, so as to be left temporarily in the ground at suitable distances apart. The number of laths required will entirely depend upon the intricacy of the ground and the size of the features. Laths are placed in positions determined by levelling at such points as will best define the shape of the contour, and these laths are afterwards surveyed in a similar manner to points in a fence. It is advisable only to level and lath out as much as can be surveyed before leaving the ground for the day.

Should the contour pass round the shoulder of a hill, so that the staffman in approaching the next point is out of sight of the surveyor at the instrument, or should the distance become too great for the staff to be distinctly read through the telescope, the instrument must be moved to a fresh position, and the levelling connected. Suppose, after fixing the contour laths marked A, the surveyor decides to shift the instrument, and directs the staffman, for the purpose of securing accuracy in the change, to hold the staff upon the changing peg or footplate. If the foresight reads

9'31, the height of the changing point will be o14 above the contour level. Hence, when the instrument is re-set up in the new position, if the back sight reads 6'78, the intermediate sight for fixing the contour laths marked B in the diagram must be 6.92, so that the reduced level may again become 120'00. In like manner when again changing the position of the instrument between the contour laths marked B and those marked C, if the changing point be 006 below the contour level, the intermediate sight then taken must be 006 above the back sight 8:29, in order to arrive at the correct reduced level for continuing the line of contour. It will thus be seen that by reducing the Level Book in the field as the work proceeds, the contour points upon lines of equal level can be most readily determined.

When an extensive contour plan is required to be completed in a short time, one set of men may be engaged to fix the contour laths by a process of levelling, and another set of men to survey them, but when more than one line of contours is set out upon the ground, it is necessary to carefully distinguish between the laths indicating the higher and lower contours, and for this purpose three distinct sets, painted respectively either red, white, and blue, may be employed to be used in turn, one set after the other for the individual contours.

In practice an intelligent man may very soon be made to get into the way of judging the correct distance or height to traverse; which is a considerable saving of time to the surveyor.

In contouring a small enclosure the theodolite sometimes is set up level in such a position that by clamping the vertical arc the required contour can be traced completely round; but when the area is of some extent the process illustrated in the diagram by means of a Dumpy level and staff is by far the most satisfactory. In order to prove the accuracy of the day's work, it is well to leave off levelling upon a bench mark as when taking an ordinary section.

Contour lines may be required to be traced round isolated features of ground for setting out water channels, railways, or for other purposes. In contouring a mountainous country the watershed of the small ranges which project