After having found Heinrich Wild's first two theodolites he designed for (or had design features by him) for Carl Zeiss, the Carl Zeiss ThI and Carl Zeiss RTh II, it was now time to get Wild's first own theodolite.

After his years as a manager of the Geo department of Carl Zeiss, Heinrich Wild started his own company in 1921.¹ In 1923 the first two theodolites that were produced within his own firm, were checked out and called the "Wild ThI".² This instrument were soon renamed "Wild T2" and would keep that name until production stopped in 1996. The instrument was an improved version of the ThI he had made for Carl Zeiss, and although being a smaller archetype, design-wise the looks hardly changed for the next 50 years.

The improvement mentioned consisted of the telescope for circle reading (see adjacent image), which was now placed directly next and fixed to the ocular of the main telescope, a feature found on most later optical theodolites. As a result of this the observer only needed to move his head by a small amount to read the circles.

The archetype T2 was produced between 1926 and 1936 and one from 1929 came up for sale in May 2012 on an international on-line market place. A befriended collector kindly pointed me to it. Only one other person seemed to be interested in this rare instrument, which was incorrectly dated by the seller as a 1940's instrument. Luck turned out to be on my side and the instrument ended up in the collection.

The container of the instrument shows its provenance (see figure 3). It is labelled "FAIRCHILD AERIAL SURVEYS", a company that created cameras for map making and aerial surveying, founded by Sherman Fairchild in 1921. Sherman Fairchild matriculated at Harvard University in 1915 and invented the first synchronized camera shutter and flash. Later he developed an improved aerial camera and in February 1920 he established the Fairchild Aerial Camera Corporation (predecessor of Fairchild Camera and Instrument) and in 1921 he formed Fairchild Aerial Surveys (and Fairchild Aerial Surveys of Canada in 1923). His cameras became the standard for aerial photography. Like Heinrich Wild he always kept an eye out for opportunities to create or improve upon existing technology or capabilities. In 1965 Fairchild sold Fairchild Aerial Surveys to Aero Services, Inc.

This early T2 is equipped with glass circles (90mm diameter horizontal and 45mm diameter vertical) and a optical reading mechanism.⁴ The T2 does not have a compensator for the vertical index, a coincidence level is used instead (see figure 8). The circles of the T2 differ from the 1924 Zeiss Th1 for both the horizontal (75mm at the ThI) as the vertical (50mm at the ThI) circle.⁵ The horizontal circle would remain the same in diameter over the years, while the vertical would grow to 70mm in later models (see figure 2).⁶

This T2 has sexagesimal circles divided in degrees down to 20 arc minutes intervals (see figure 12 and figure 13), can be read using a micrometer directly to 1" and estimated to about 0.1". The vertical circle is illuminated by two distinctive prisms on two sides of the telescope (see figure 6), that are typical of this archetype T2. The horizontal circle is illuminated by a prism at the base were later T2s would have a mirror (see figure 7). Finally the micrometer is illuminated directly and has a rotatable glass reflector, which sadly enough is missing on this T2 (see figure 3). It probably got lost as the reflector was made of sandblasted glass which not only acts as a diffuser, but even reduced the amount of light available. Tests with the T2 showed that it is fully functional without it and that the micrometer is even better illuminated than the circles. Most probably it would have been for this reason that people took it off, after which it got lost. This particular version of the T2 is already equipped with wiring for artificial illumination, a feature that was not yet standard at the time. The light bulbs are however missing.

Commercial production of this archetype model T2 started in 1926 and lasted until 1936. It was produced in three series, which saw two changes over the years.

The very first models were painted black/grey, similar to the Zeiss instruments, or black/green. The first change meant that the colour became green throughout, while the second change meant that the inverter knob for reading the two circles was improved.

The instrument shown here is one of that third series in green with the improved inverter knob. Of the very first black and white model some 200 instruments were made, while of the second model 1593 instruments saw the light.

With a total of 2515 archetype T2s being made this means that the T2 shown here was one of 722 of this third archetype model. The T2 would become one of the most popular - if not the most popular - universal theodolites. In total 38,800 T2s were made up to 1970 and many more thereafter.

[1]: Heinrich Wild at Carl Zeiss Jena

[2]: H. Baertlein, Inside the Leica TCA2003

[3]: Wikipedia: Sherman Fairchild

[4]: O. von Gruber, 'Neue Theodolitkonstruktionen', in: Carl Zeiss Jena Leaflet: GEO 57, (1927), p. 8.

[5]: Carl Zeiss - Jena, 'Zeiss Theodolite - Theodolit I mit selbststättiger Mittelbildung, gemeinsamer Ablesung und optischem Mikrometer', in: Carl Zeiss - Jena, Leaflet: Geo 60, (1926), p. 5.

[6]: F. Deumlich, Surveying Instruments, (Berlin / New York, 1982), p.120

[7]: With many thanks to J. Dedual of the Virtual Archive of Wild-Heerbrugg for these historic details.