96 
HINTS TO TRAVELLERS. 
a round of bearings to A, C, D, E, &c. These bearings are now plotted, 
and their intersections with the bearings from A fix 0, D, E, &c.; in this 
manner a rough triangulation is established, and a number of points fixed, 
by the aid of which the detail can be filled in. 
The paper, or field-sheet, for sketching with a prismatic compass, 
should have parallel lines at unequal distances ruled upon it, to be 
considered as east and west lines. 
4. Survey of a plot of ground containing ruins , dec .—In making a survey 
with a tape alone, we are confined to the simplest geometrical figure—-the 
triangle, as it is the only one of which the form cannot be altered if the 
sides remain constant. In carrying out such a survey, divide the surface 
into a series of imaginary triangles, as large as the nature of the ground 
will admit of, and attend to the following rules 
1. Do not be in a hurry to commence work, but walk over the ground, 
and make a rough eye-sketcli of it on paper. 
2. Select two points, as far apart as possible, visible from each other, 
and commanding a good view; let the points bo near the boundaries of 
the ground, and so situated that the line joining them forms a sort of 
diagonal; this becomes the main line. 
3. Select a point on each side of the main line, near the boundary of 
the work, to which lines can be measured from each end of it, thus giving 
two large triangles; then measure a check, or tie line, from one of the 
vertices to a point at, or near the middle of the opposite side. 
4. On the sides of these triangles, erect smaller ones to embrace all the 
ground to be surveyed. 
5. Measure lines from any station laid down, or from any part of a line 
connecting two of them in directions most convenient for obtaining the 
detail, taking offsets to such objects as present themselves. 
The interiors of large buildings should be measured in a somewhat 
similar way, by dividing them into imaginary triangles, and measuring 
tie lines. 
The great principle in all surveys is to work from a whole to the parts ; 
errors are thus subdivided and time and labour economised. 
