Astronomic equipment used during Op Emily

Wild t4 theodolite

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. but on occasion we used WWV and others

Chronometer and Chronograph
A Mercer second chronometer was used in conjunction with a mercer tape chronograph
pictured below.
The chronograph was modified to use side moving pens instead of the normal needles because the signal from the radio was not sufficient to pierce the tape.
Signal from the impersonal micrometer on the T4 came to the chronograph by wire.
The timekeeping equipment was housed in a Morris Commercial 2*4 office vehicle and power came from a  petrol driven generator on  a trailer
shown below is a similar vehicle in a different livery

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 Surveyors

Peters 8 figure table of natural trigonometric functions

calculating machines used included

Brunsviga double bank machine


Facit K


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