1939 Wild Heerbrugg T3 geodetic theodolite
Several years ago I obtained a sexagesimal Wild T3, one with an astronomical reticle and circles divided in degrees. As here in the Netherlands theodolites were used with mostly centesimal divided circles, I was eager to find a similarly divided T3. Most T3's have however been produced with sexagesimal divisions so the chances are extremely rare to find one, or at least that is what I thought until 2013.
That year a geodetic T3, made in 1939 (see figure 16) and once owned by the Středisko elezniční Geodézie Praha (Centre for Railway Geodesy in Prague), came up for sale on the largest on-line auction site. Not only was it once again quite an old T3, this time it was centesimally divided, just what I was looking for. In addition to that it proved to be in even better condition than my astronomical T3.
Together with the Carl Zeiss ThI and archetype Wild T2 the T3 was one of the first theodolites to feature glass circles (135mm diameter horizontal and 90mm diameter vertical) and an optical reading system, after Heinrich Wild's Zeiss ThI. The T3 does not have a compensator for the vertical index, a large coincidence level (see figure 9) with a settling accuracy of 0.5" is used instead.1
Unlike the astronomical and most other T3's this one is equipped with centesimal circles (divided in gon where 400 gon makes a full circle) and can be read down to 0.0001gon and estimated to 0.00001gon or better (see figure 12). Here in the Netherlands centesimal T3 have been have been used by the Dutch government (see below).
The accuracy of the direction reading is given as 1.5cc (0.00015gon).1 Reading the circles is easier than with the astronomical T3 as the micrometer scale of this early model is divided in 50 mayor intervals spanning 0.05gon in total and is numbered 0-50 (see figure 12). The mayor intervals are subdivided into 10 parts each, making each division 1.0cc (0.00010gon).
In contrast to the astronomical T3 the micrometer scale readings do not need to be multiplied by 2 in order to get the actual reading, but instead can be easily added to the direct circle reading (see figure 12).
Use and diffusion in the Netherlands
This section is identical to the same section of the astronomical T3.
Up to 1970 only 6,860 T3s were produced by Wild (compared to the 38,800 T2s for the same period this was a limited production).2 The T3 was only used in small quantities here in the Netherlands.
The first T3 probably entered the Netherlands when the Bijhoudingsdienst der Rijksdriehoeksmeting (Maintenance Division of the Dutch Trigonometry Department) received one on loan for three months from Wild-Heerbrugg in 1931.3 The instrument was found to be equal in quality to the Wanschaff theodolites used until then, but saved time and money as observations could be done without assistance and circle readings while keeping ones stance (for which it was no longer necessary to create large structures around the instrument).3
Having great practical and economical advantages, in December the following year it was decided to purchase one T3 for second order measurements.4 Up to at least 1937 this T3 remained the only one and was exclusively used by the survey crew of land surveyor Meertens, while the other crews still used the Wanschaff's.5 Based on the serial numbers another T3 was purchased a decade later. These early T3's were sexagesimal instruments. In order to speed up the calculations - which at the time were done using calculators of Brunsviga and Marchant, like the Brunsviga Models D13 R/2 and 13ZK and the Marchant Pin Wheel6 - the instruments were sent back to Swiss to have them modified to the centesimal system.7
Soon after other institutes and companies in the Netherlands started using T3s as well, but so far I have traced only seven of them; at least two were used at the University of Delft (serial no's 26595 and 33172) and still remain in their collection. The 26595 is a T3R (Recording) on which it was possible to mount a camera on the tube to photograph the circles, allowing interpretation afterwards using a microscope.8 At least another two were owned by GrontMij and sold when they became redundant (one of which with serial no 82980 is in the collection of a colleague) and at least three (but possibly four or even five) were used by the Dutch triangulation division Rijksdriehoeksmeting of the topographical department Kadaster (two instruments with serial numbers 18815 and 74314 still remain in the collection of the Kadaster Bedrijfsmuseum, for the 74314 see picture 23 on their web site).9,10
In contrast the Wild T2 was one of the most popular instruments among land surveyors here in the Netherlands in that period and were used probably in their hundreds.11
For more information on Wild Heerbrugg, see the Swiss Wild Heerbrugg virtual archives.
This T3 came complete with its original container, all three oculars, lamps, and leather lens cap (see figure 3 and figure 6). The three oculars allow to use the instrument with varying magnifications of 24x, 30x and 40x (see figure 6). The instrument showed here is centesimal divided (400 divisions in a full circle), while the astronomical Wild T3 in my collection is sexagesimal divided (so in degrees, minutes and seconds).
Another major difference with the astronomical T3 is the reticle (see figure 7). Where the astronomical T3 is invested with stadia hairs this geodetic T3 does not have a single one. In addition to that the vertical line of the cross-hairs is reduced to a tiny vertical dash to ensure that observations were always done at the centre of the field of view.
The instrument is in very good shape. The paint slightly differs in colour from the other T3 (see figure 5), it was however not uncommon that Wild experimented with it. Other parts of the instrument also differ from the 1937 T3; the black parts and all the knobs have a high polished finish whereas these have a silk finish on the earlier instrument.
: Wild Heerbrugg, Wild T3, Instructions for Use, (Switzerland, 1983), p.6.
: Verslag van de Rijkscommissie voor Graadmeting en Waterpassing aangaande hare Werkzaamheden over het Jaar 1931, p.4.
: Z. Klaasse, Inventaris Bedrijfsmuseum Kadaster, Deel 2. e.Ruilverkaveling, f.Schepen, g.Consignatie van Effecten aan Toonder, h.Inventarissen van Archieven en Meubilair, i.Landmeetkundige Instrumenten, j.Tekenmateriaal en Kantoorbenodigdheden., (Apeldoorn, 2010), pp.125-127.
: With thanks to former employee Ton Zijderveld for his memories on this matter.
: With many thanks to J. Dedual of the Virtual Archive of Wild-Heerbrugg for for explaining this to me.
: Z. Klaasse, Inventaris Bedrijfsmuseum Kadaster, Deel 2. e.Ruilverkaveling, f.Schepen, g.Consignatie van Effecten aan Toonder, h.Inventarissen van Archieven en Meubilair, i.Landmeetkundige Instrumenten, j.Tekenmateriaal en Kantoorbenodigdheden., (Apeldoorn, 2010), p.70.
: Ministerie van Volkshuisvesting en Ruimtelijke Ordening, '2.Rijksdriehoeksmeting', in: G.J. Bruins W.A. Claessen, Serie Landmeetkundig Perspectief Dienst van het Kadaster en de Openbare Registers, (1979), pp.31,34. According to former Kadaster employee Jan Stehouwer several T3s were sold to Rijksdriehoeksmeting employees when they became redundant and as the Rijksdriehoeksmeting had five cars for the transport of surveyors and instruments it is possible that there were even five (given the policy that each car had a theodolite). In addition to that the first survey exclusively done with multiple T3s was done in 1956, which is earlier than the second surviving T3 in their collection. According to Ton Zijderveld they used three T3's in the 40s and had army cars to transport them. These cars were replaced by four Fords in 1952 and would therefore accomodate four instruments.
: All firms I worked with had at least one or two of them and so do most collectors I know. At the survey department of Rijkswaterstaat each land surveyor had one in his car and around 2001 I witnessed some 40 of them (all old model) being made redundant in one large clean-up.
If you have any questions and/or remarks please let me know.
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 1950s Askania Tu400 1952 Wild RDH 1956 Wild T0 1960s Zeiss BRT 006 1961 Wild T1A 1961 Wild MIL-ABLE T2 1962 Wild T2 1963 Wild RDS 1966 Kern DKM2 1969 Wild T2E 1969 Wild Di10 / 1972 T2 1976 Wild Di3S / 1963 T2 1976/79 Wild T2 mod - DI4 1990 Wild T2 mod - Di1000