42 
HINTS TO TBAVELLEBS. 
The TaUe. —A is a rectangular board of well-seasoned wood, and can, 
within certain limits, be made of any size to suit the work intended to be 
done. To this board the paper to be drawn on may be attached either by 
drawing-pins, clamping-plates, or a box-wood frame, E, which is usually 
graduated in the same manner as a protractor, and can be used to 
measure horizontal angles, when the fiducial edge of the ruler is placed 
against a pin in a small hole, in a brass plate in the centre of the table, 
which is provided for the purpose. A stud, on the under part of the 
table, fits into a socket in the tripod , F; the table can then be revolved 
to any horizontal position, and there fixed by tightening the large nut, G, 
on the clamping-screw attached to the stud. 
The Tripod, F, should be a split one, and for convenience of packing 
the legs should telescope. This arrangement is also convenient for 
setting up the instrument on sloping ground. The screws for tightening 
the tripod legs should be enlarged at the end so as to prevent their falling 
out. In many cases it will be convenient to have the plane-table tripod 
so made that it can be used for the other instruments. 
The Alidade, B, is a flat ruler, having a fiducial edge, each end of 
which carries a sight-vane. In the sight-vane, three or four small holes 
should be drilled at intervals, as it is often very difficult to see objects 
through the slit. On the centre of the ruler is a small circular level, 0, to 
be used in setting up the table. In mountainous countries a small tele¬ 
scope fitted on the alidade will be found very convenient, and where this 
is not the case, and the elevation or depression of an object to be intersected 
is more than can be embraced by the sights, the intersection must be 
effected with the assistance of a plummet suspended in the exact ray, 
either before the object sight or behind the eye-sight as may be required. 
The Compass, D, should have a needle about four inches long, contained 
in a rectangular metal box, and is so arranged that when the needle 
points to north it will be parallel to the outer straight edge of the box. 
A pair of compasses, paper, india-rubber, pencils, a pen-knife, and some 
pins, complete the essentials for plane-table work. 
It is not considered necessary, in these Hints/’ to give any detailed 
description of the more elaborate forms of the plane table, but any 
person desiring information on the subject can obtain it by applying 
to the Instructor at the Society’s rooms. ( For instructions for using this 
instrument in the field, see pp. 97 to 109.) 
