205
and 4.15 m long was carved along the beam, into which two metal rods, one of brass
and one of iron, were housed. Two thermometers were inserted horizontally at the
ends of the tesa to calculate the expansion of the metal rods. A bubble level was
placed at the center of the tesa. The ends of the tesa were placed on two tripods
which could be moved with worm screws.
To allow the measurements to be taken along the (average) sea level geoid, it was
necessary to find the altitude of the road. As a reference they used the Cloaca
Maxima, whose altitude had been measured in 1822 by the pontifical engineers to
be 5.907 m above sea level. With these measured levels and knowing the leveling
Fig. 12.3 Endpoint B, discovered in 2013. (Credit: the Author)
12 The Measurement of the Geodetic Baselines Along the Via Appia Antica
and 4.15 m long was carved along the beam, into which two metal rods, one of brass
and one of iron, were housed. Two thermometers were inserted horizontally at the
ends of the tesa to calculate the expansion of the metal rods. A bubble level was
placed at the center of the tesa. The ends of the tesa were placed on two tripods
which could be moved with worm screws.
To allow the measurements to be taken along the (average) sea level geoid, it was
necessary to find the altitude of the road. As a reference they used the Cloaca
Maxima, whose altitude had been measured in 1822 by the pontifical engineers to
be 5.907 m above sea level. With these measured levels and knowing the leveling
Fig. 12.3 Endpoint B, discovered in 2013. (Credit: the Author)
12 The Measurement of the Geodetic Baselines Along the Via Appia Antica