Wild t4 theodolite and
The Wild T4 micrometer theodolite is the largest of the Wild theodolites and is used for angle measurements of the highest accuracy in 1st order triangulation, tunnel staking, geodetic astronomy and similar precision applications. The theodolite is of the "broken telescope" type, which means that the image formed in the telescope is viewed through an eyepiece placed at one end of the trunnion axis. Its powerful telescope, with approximately 60x magnification, allows comfortable sighting to zenith, because the eyepiece with its 'impersonal micrometer' is always at eye level. Horizontal and vertical circle readings are made with the optical micrometer directly to 0.1" and 0.2" respectively, by coincidence readings of diametrically opposite graduations. It is capable of determining the longitude to 0.01" of time, latitude to 0.2" of arc and the azimuth to 0.3" of arc.
The diameter of the objective lens of the telescope is 70 mm, its focal length (f) is 578 mm, and due to its powerful magnification, the shortest sighting distance is approximately 100 metres. The diameters of the horizontal and vertical circles are 240 mm and 135 mm respectively. The sensitivity of the altitude bubble for the vertical circle is 2" per 2 mm. The sensitivities of both the hanging level, and of the two Horrebow-Talcott levels supplied with the instrument are 1" per 2 mm.
The circles are to the best of my recall graduated to 4' of arc
The Wild T4 is world-renowned as the ultimate in theodolites and is undoubtedly the largest among the Wild range. Weighing approximately 60 kg, it is also a fairly heavy and solidly built instrument. The telescope assembly has to be removed for transportation. There are separate cases for the alidade, telescope & suspension level.
Radio receiver for time signals
The RCA AR88 is a superhet 20 valve receiver, the one used had an extra circuit fitted in order to activate the Mercer chronograph.
Time signals mainly used were from MSF at Rugby.
Signals from the T4 were by wire.
A Mercer half second Chronometer was used for timekeeping.
The chronograph was also modified to use sideways acting pens instead of the normal needles as the signal was insufficient to perforate the paper tape.
Thank you to Brian for finding these pictures
The Astro Equipment was housed in an Office Vehicle
A Morris Commercial Office vehicle 4*2
The picture shown is in a different livery and is the copyright of Richard Huelin.
Thank you to Richard for permission to use this image
Initial calculations were performed using
Data from "Apparent Places of Fundamental Stars."Star almanac for Land SurveyorsPeters 8 figure table of natural trigonometric functions
calculating machines used included
Brunsviga double bank machine