1956 Wild Heerbrugg T0 boussole theodolite

1956 Wild Heerbrugg T0 boussole theodolite
Figure 1: 1956 Wild Heerbrugg T0 boussole theodolite
Another superb find in 2012, almost even better than the Wild T3 I found this year; a 1950s Wild Heerbrugg T0 boussole theodolite. The T0 was Heinrich Wild's vision on the well known American transit like the 1919 K&E.

Provenance
The instrument has been used for forestry works in Fruška Gora, one of the national parks on the border of Syrmia, Serbia, and Croatia (although most of it lies in Serbia).

The previous owner's grandfather, forestry engineer Vlatko Radanovic, used to work with the forestry department which used these type of instruments for all kind of measurements back in the 1960s when the national park was founded. They were however decommissioned some 20 years ago, even before Vlatko was employed.

After his retirement Radanovic took the instrument home and his grandson had the instrument recently listed on the largest on-line auction site. Two days later I was the highest bidder and the instrument made his way to the collection.

Accuracy
The T0 definitely is not the most accurate theodolite Wild ever produced. It has however one great advantage over all other Wild theodolites; the boussole. Thanks to it traversing could be done much quicker than by using a normal theodolite or total station as one can skip half the stations needed for the same traverse. Boussole theodolites were not uncommon, especially in the U.S.A. where most theodolites - or transits as they named them - were equipped with boussoles.

The difference with all other boussole instruments was the way they were read. Up to the Wild T0 most boussole instruments were read at two diametrical opposite sides separately, simply by estimating the position of the two ends of the needle against a circle divided in whole degrees only.

The Wild T0 however did this the same way as all other Wild instruments: by superimposing the image of two diametrically opposite parts of the compass circle on top of each other (coincidence reading). In addition to that the boussole of a Wild T0 can be locked in its position (see figure 11), by which the instrument becomes a normal theodolite.

The Wild Heerbugg T0 from the other side.
Figure 2: The Wild Heerbugg T0 from the other side.
Reading the circle could now be done in whole degrees directly on the circle, in whole arcminutes using a micrometer, and estimated a further decimal (see figure 15).

The vertical circle is levelled using a plain vial with a sensitivity of 4' per 2mm (see figure 5). The circle is read directly to 10 arcminutes and can be estimated down to a single arc minute (see figure 16).

Production
The Wild T0 was first produced in 1932 and saw only two changes until production stopped in 1990. The model shown here is of the first series which ran until 1972 and dates from about 1956. Up to 1970 some 12,000 were produced, about double the amount of T3's (6860), a third of the amount of T2's (38,800), and a quarter of T1's (51,980) for that same period.

According to the Ahrend Prijscourant 22 a few years later, in 1962, a "T0 in metalen stolp, zonder statief, 400g..." ("T2 in metal cover, without tripod, 400g") would have cost fl.1,397.-.1

The instrument
The instrument came complete with its steel container (see figure 3), the base of which is an integral part of the instrument. Apart from the boussole this is another feature not shown on other Wild theodolites. At the underside of the base a lid can be opened to access the threaded hole for attaching the instrument to a tripod (see figure 12). Being a boussole instrument this tripod (models 2a and 2b) had to be free of iron.

The instrument is rather small, even smaller than the archetype Wild T2 (see figure 4). The telescope has a magnification power of 20 times. The reticle is different than most instruments as it has two sets of stadia hairs. Two on one side of the vertical cross-hair and two at the other. The allow distance measurements with the usual 100 and less common 50 multiplication constant (see figure 14, where the ones at the right are the ones for 100x).

Notes

[1]: Ahrend, Prijskoerant 22 Meten, (1962), pp.20-21.

If you have any questions and/or remarks please let me know.

The T0 with its container.
Figure 3: The T0 with its container.
 
The Wild T0 compared to the archetype Wild T2.
Figure 4: The Wild T0 compared to the archetype Wild T2.

The vial for the vertical circle.
Figure 5: The vial for the vertical circle.
 
The glass window for illumination of the vertical circle.
Figure 6: The glass window for illumination of the vertical circle.

The selector knob for viewing the boussole through either the left or right ocular.
Figure 7: The selector knob for viewing the boussole through either the left or right ocular.
 
The boussole is illuminated by two of these windows.
Figure 8: The boussole is illuminated by two of these windows.

The micrometer for the boussole.
Figure 9: The micrometer for the boussole.
 
For convenience the micrometer is divided on both sides.
Figure 10: For convenience the micrometer is divided on both sides.

The boussole can (and should) be locked (right position) for transport.
Figure 11: The boussole can (and should) be locked (right position) for transport.
 
The instrument is mounted on a tripod directly through its base.
Figure 12: The instrument is mounted on a tripod directly through its base.

Rough aiming is done by a peep-sight and bead.
Figure 13: Rough aiming is done by a peep-sight and bead.
 
An inverted view through the telescope revealing four stadia hairs.
Figure 14: An inverted view through the telescope revealing four stadia hairs.

A view at the boussole at 189°-40.8'.
Figure 15: A view at the boussole at 189°-40.8'.
 
The vertical circle has no micrometer and is read and estimated directly (106°-04').
Figure 16: The vertical circle has no micrometer and is read and estimated directly (106°-04').

Surveyor's crosses Geodetic Sextants Theodolites Total Stations Levels Standards Tools Firms
19th C. SDL 1919 K&E 1926 Zeiss RThII 1924 Zeiss Th1 1929 Wild T2 1937 Wild T3 (astronomic) 1939 Wild T3 (geodetic) 1943 CT&S Tavistock 1948 Wild T1 1952 Wild RDH 1956 Wild T0 1961 Wild T1A 1961 Wild MIL-ABLE T2 1962 Wild T2 1963/76 Wild T2 - DI3S 1963 Wild RDS 1966 Kern DKM2 1969 Wild T2E 1976/79 Wild T2 mod - DI4 1990 Wild T2 mod - Di1000 20th c. Askania Tu400