Levelling rods. Levelling rods
are of two types, target and self – reading; the former is read by a rodmen,
the latter by a levelmen. The commonest forms of target rods are the Boston, the New York and
the Philadelphia; the Philadelphia can be used also as a self-
reading rod. Most rods are made of two or more sections, so that they may be
extended. The target of the Boston
rod is permanently fastened to one strip of the rod. The other target rods are
always used right – side up and have movable targets. The New
York rod has a vernier for reading to a thousandth of a foot; most Philadelphia rods have a scale resembling a
vernier, which gives the hundredths and makes it easy to estimate thousandths,
thus serving every purpose of a vernier. All these rods are usually 6 or 7.5 ft. long and are extensible
for readings up to 11 or 13 ft.
They are also made 3 ft.
long, with extension to 5 ft.
and 5 ft.
long with extension to 9 ft.
for use underground.

 

A self – reading rod has
graduations (usually every tenth of a foot) painted on its face, so that it can
be read through a telescope by the levelman. The figures on the face of the rod
are usually of a definite height (0.06 or 0.08 ft. ) and of a
thickness of 0.01 or 0.02 ft.,
thus aiding the levelman to estimate hundredths of a foot or even closer.

 

Engineer*slevel
is a telescope to which a delicate spirit level is attached parallel to the
line of sight, so that when the bubble is in the centre, the line of sight is
horizontal. The two common types are the Y- and dumpy – levels. In both the
telescope is mounted on a vertical axis about which the telescope can swing
horizontally and is leveled by 4 levelling screws.

 The Y- level has its spirit level attached to
the telescope which rests in two Y- shaped supports fastened to a horizontal
bar rigidly connected to a vertical axis. The telescope can be taken out of the
Ys, turned end for end.

The dumpy – level has its
vertical axis, a horizontal bar and supports for the telescope all cast in one
piece to which a spirit level is attached. The dumpy – level will stand much
rougher use than Y – level.

 

 
Дужеее потрібний перевод,допоможіть будь - ласка(((((((((