Wild T4

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Scientists with a Wild T-4 in the Nebraska Sandhills .

The Wild T4 is a large universal instrument from the Swiss company Wild Heerbrugg . It is a special instrument for astro-geodetic measurements; its production was stopped around 1980 because of the tight market. There are around 100 copies worldwide.

Due to its high stability, its substructure was made or adapted for other instruments as well as for the large theodolites . a. for the satellite cameras BC-4 of the world network from 1969–1974.

The T4 is designed both for triangulation in the first-order network and for high-precision astronomical positioning . He has a broken telescope with a 60 mm aperture and 550 mm focal length, which is provided with a dew cap to prevent the nighttime cooling . The magnification is 65 times, the beam path is deflected laterally by 90 ° in the center of gravity of the telescope by a deflecting prism, so that from there it runs in the tilting axis . This construction combines several advantages:

  1. the telescope can be tilted up to the zenith (and beyond), which is essential for stargazing,
  2. the side eyepiece is comfortable for the observer
  3. and moreover always horizontally and at the same height,
  4. the overall length is shortened, which reduces the bending of the telescope and thermal influences,
  5. the telescope is well balanced (kink point exactly at the intersection of the tilting axis - standing axis ) and can therefore be easily rotated despite its length,
  6. the tilting axis is accessible for rider or hanging vials .

The latter aspect of course requires careful maintenance in order to prevent any hint of rust in damp weather or dew .

The eyepiece has an impersonal micrometer ; H. the moving thread can be tracked to the observed star in order to reduce the reaction time and the aiming errors . It can be swiveled as desired so that oblique star passages can also be observed.

The pitch circles made of optical glass are very finely divided (by 2 to 2 arc minutes ) and have a diameter of 25 cm (horizontal circle) or 15 cm (height circle). They can be read off with flat plate micrometers at two opposite points; the accuracy of the reading is a few 0.01 ″ . The partial circles and the field of view are provided with adjustable lighting.

The vertical axis is designed as a maintenance-free cylinder axis with ball bearings on top , the tilting axis, which is around 30 cm long, is in adjustable V-bearings.

A very precise, lightable hanging vial (Parswert under 1 ″) and a Horrebow double vial, as well as connections for the chronograph, are to be mentioned on important additional devices .

For transport, the telescope is lifted out of the tilting axle bearings and the upper part is fixed in a flat transport box , while the conical lower part with the alidade can be stored in a deeper box.

The use of the T4 in national surveying began in the interwar period and was mainly used for basic surveying (triangulation) and astrogeodesy (determination of astronomical latitude and longitude, astronomical azimuths ). In Switzerland and Austria , its use was limited to the foothills of the Alps and easily accessible mountain peaks, while in the high mountains the lighter and more compact DKM3-A from the competitor Kern Aarau was preferred.

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