1948 Wild Heerbrugg T1 theodoliteIn August 2014 this Wild Heerbrugg T1 with original steel domed container and wooden pyramid transportation box arrived in the collection.
Originally designed in 1933 the instrument was the less precise sister of the Wild T2. The instrument was dubbed 'Double Centre Theodolite', probably as it was the first Wild Heerbrugg theodolite to have an exchangeable tribrach (see figure 6), quite similar to the one of the Carl Zeiss ThI Heinrich Wild designed in the early 1920s.
The T1 has a similar vial for the vertical circle as the Wild T0, which was replaced in 1957 by a liquid compensator to create the Wild T1A (the A stands for "Automatic"). Thanks to the compensator it was no longer required to fully level the instrument to obtain a vertical angle within the specs of the instrument.2 This Wild T1 here, however, still has the old normal vial.
The T1A would be followed by the T1A-E - "E" for the "Erect" field of view - in 1959.2 It would become the first Wild theodolite - and perhaps the first theodolite at all - to feature an automatic compensator for the vertical circle.
In contrast to the other Wild theodolites produced so far, the Wild T1 was a true repetition theodolite like the Carl Zeiss RThII. For this purpose the instrument has "...two independent cylindrical vertical axes and two horizontal clamps (one each for the lower and upper plate and shaped differently to avoid confusion)..." (see figure 9).1
The 79mm diameter glass circles of the Wild T1 are not read by the coincidence method at two diametrically opposite locations, but by comparing one end of the circle to a double reference line using a micrometer. Both the horizontal and vertical circles are read directly down to 0.01gon by means of the micrometer and estimated to 0.001gon (see figure 15).
The vial for the vertical circle has an accuracy of 1' per 2mm run, while the plate level has an accuracy of 30".
Between 1933 and 1970 a total of 51980 Wild T1's have been produced, including all varieties on the model like the T1A, T1E-A etc. In this respect it has been the most productive Wild theodolite for this period and only surpassed in quantity by the Wild levels N1 and N2).4
According to the Ahrend Prijscourant 44 of 1954/55 a "T1 ... in metalen stolp, met toebehoren, transportkist met kussens bekleed en statief..." ("T1 ... in metal cover, with accessories, transportation box padded with cushions and tripod") would have cost fl.1,743.50.5
This particular Wild T1 is in very good condition and came complete with its original container and transportation box (see figure 3 and figure 4). As with all other Wild theodolites the T1 has been produced as sexagesimal and centesimal instruments. The one showed here is a centesimal one.
It is similar in size as the archetype Wild T2 and thus slightly smaller than the later editions of that model. Its telescope has an inverted view with a 30 times magnification, similar to the Wild T2, and has four stadia hairs; two on the vertical cross-hair and two on the horizontal one (see figure 14). The stadia multiplication factor is 100.6
Another nice feature for an early 20th century instrument like this one is the optical plummet. This was a reasonable recent addition to Wild theodolites and implemented in a much better way than on later Wild theodolites. The difference with those later models is that on the T1 the optical plummet forms an integral part with the yoke of the instrument (see adjacent picture). Thanks to this the optical plummet can rotate with the instrument allowing to easily check its proper adjustment. Later theodolites would have the optical plummet in the tribrach and therefore fixated with it in one direction.
The optical plummet can be focussed by pulling it out of the yoke (see figure 2), while the circular 'cross-hair' (see figure 13) can be focussed by rotating the tube.
Notes: See Wild Theodolites and Accessories for every Survey Task: T1A. at the Virtual Archive of Wild Heerbrugg
: See the theodolite overview page at the Virtual Archive of Wild Heerbrugg.
: Wild Heerbrugg, Wild T1, Micrometer Theodolite with Automatic Vertical Index, instructions for use, (Heerbrugg, 1975), pp. 10,12-13.
: See the Products: Quantity at the Virtual Archive of Wild Heerbrugg.
: Ahrend, Technische Prijscoerant nr. 44, 1954/1955, (1954), p.157.
: See the Technical Data Wild Theodolites page at the Virtual Archive of Wild Heerbrugg.
If you have any questions and/or remarks please let me know.
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