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Road projects. ANEROID BAROMETROS.
A method of quite fast leveling although very little used is that that is based
on the use of the aneroid barometer, which gives the level differences starting
off of the measures of the atmospheric pressure in the points in question. The
atmospheric pressure is exerted on the cover of a closed cylindrical box, with
an inner emptiness, whose deformations are amplified and transmitted to an
instrument needle. It has small errors due to the mechanisms and means, in spite
of being of metals different to compensate temperature variations. In the
barometric leveling the following procedure of field is used: First, it is
necessary to place the altimeter on a point of well-known level and to fit it so
that the reading is indeed this level. Immediately the instrument takes to the
points whose levels are desired to know and in each one of them it registers the
corresponding reading and the hour in which this one took place. Normally, the
atmospheric pressure varies in appreciable form during small periods of the day,
in view of which two altimeters are used; one is placed in the first station (of
well-known level) and at intervals regular readings of reference are taken. As
they advance the works, the hour of each observation done with the other
altimeter is written down carefully, in the other points and this way the
readings of the heights carried out in the same one are corrected. The last
observation in the traveling altimeter will have to be done in the initial
station like verification means. The heights determined with an ordinary
barometer that it takes from a point to another one can give errors of several
meters. Nevertheless, using special extraordinarily sensible and technical
barometers, heights of a greater meter can be determined accurately or.
BRUJULAS. For the obtaining of courses the compass is
used, which is useful only for approximate rises. They are hand generally
instruments. They can lean in a cane or a twig any. When a line of vision in
certain direction goes, the needle of the compass (when it loosen and it is in
rest) always aims towards the magnetic north and indicates the magnetic course
in this direction. With respect to the scientific explanation of this fact some
theories suggest must to the iron that composes the nucleus of the Earth,
whereas others attribute it to electrical currents in the atmosphere due to the
terrestrial rotation. The fact is that the needle indicates the meridian
magnetic. The North and South magnetic poles are located approximately to 1,600
km and 2,496 a.m. respectively, of true the geographic poles. The lines of
magnetic Earth force that align the needle, throw of one of the ends of this one
and they make it be underneath the horizontal position. The angle of this
magnetic dip, varies of 0° in Ecuador to 90° in the magnetic poles. The made
compasses to work in the North hemisphere bring a counterbalance in the South
end to resist the magnetic attraction in the vertical sense. This aid to
identify the North and South points. The horizontal angle included/understood
between the magnetic meridian and true the geographic meridian denominates
Variation.
CLISIMETROS Or ECLIMETROS. This instrument is a hand level that serves so
much for the direct leveling as to measure the angles of slopes. Viewfinder of
square section and 127 mm in length, provided with an extension tube consists of
a tube that extends it up to 178 mm. The extension tube has a sight of hole with
horizontal reticulum in the end of the eyeglass. Screwed to the rectangular tube
of sight, there is a semicircle graduated in degrees and that is ***reflxed mng
by means of a vernier, and an axis that crosses the arc, takes an arm with a
bubble level. Within the tube 45° with respect to the line of vision is an
inclined polished affluent mirror and that allows the observer simultaneously to
see the level in the mirror and a distant point in the reticulum. In order to
measure a rake the level is placed so that the bubble in the mirror is seen. |
