Bilby towers

Bilby Tower

Bilby Tower

Bilby Tower

Bilby Tower

In their book on the Ordnance Survey, Owen and Pilbeam state:

"The steel observing tower, called a Bilby tower, had been developed in America for surveying its vast flatlands and prairies. Each tower was in fact two independent structures. The instrument was supported on the inner tower and the observer and his assistant stood on the outer one. They needed careful erecting, including the laying of concrete footings for the legs. It was found to be easier for a trig pillar to be built under the Bilby tower, once it was in position. At full heights the towers rose to 103 feet and took about 10 hours to erect"

Further detail is given in History of the Retriangulation of Great Britain .

Bilby Towers were used extensively in the re-triangulation to elevate the theodolite position in order to provide a more extensive view.

They consisted of two separate towers one inside the other. The outer tower carried the observer and booker while the inner, totally independent, carried the instrument. The towers were guyed to the ground for stability. A height of 100ft was quite common, the highest may have been 120ft. They were constructed by a special team of labourers who specialised in erecting the Bilby Towers. The inner tower was plumbed precisely over the mark using a 10lb plumb bob, sometimes suspended in an oil bath to dampen the motion.

Bilby Towers were most commonly used in East Anglia. All the Towers were sold of in the 1980s, mainly for scrap.

The following primary pillar stations had steel towers. All these pillars were built in 1938 or 1939.

Primary trig pillars which has steel towers

Grid Ref	T:UK	PP	Station Name	Location
TQ 84340 11923	TP0442	193	Fairlight Down	Hastings, East Sussex
SP 89068 09997	TP2394	204	Coombe Hill	Tring, Buckinghamshire
SU 72344 95241	TP0317	207	Shirburn Hill	Wallingford, Oxfordshire
TL 78691 55857	TP2132	236	Chedburgh	Bury St Edmunds, Suffolk
TM 18240 53814	TP0757	244	Swilland	Ipswich, Suffolk
TM 25514 70170	TP2636	260	Crown Corner	Saxmundham, Suffolk
TG 26238 02646	TP3258	261	Framingham	Norwich, Norfolk
TG 02653 32999	TP5438	263	Piggs Grave	Sheringham, Norfolk
TF 40661 73018	TP2772	265	Dexthorpe	Alford, Lincolnshire
TF 64840 04270	TP0374	424	Crimplesham	Downham Market, Norfolk
TF 83913 09253	TP6276	425	Swaffham	Swaffam, Norfolk
TF 92508 10418	TP3260	426	Fransham	East Dereham, Norfolk
TF 50203 16622	TP6713	427	Walpole St Peters	Wisbech, Norfolk
TF 00079 03199	TP2357	431	Collyweston	Stamford, Northamptonshire
TL 06666 78508	TP3128	432	Fayway	Irthlingborough, Northamptonshire
TL 05880 59778	TP7113	433	Bolnhurst	Bedford, Bedfordshire
TL 64887 22350	TP2925	437	Dunmow	Braintree, Essex
SP 85120 98887	TP6668	442	Uppingham	Oakham, Leicestershire
SP 80590 75413	TP0260	443	Faxton	Northampton, Northamptonshire
TA 24842 18824	TP6208	450	Stone Creek	Withernsea, Humberside
TA 29825 33763	TP6612	451	Tunstall	Withernsea, Humberside
TA 39598 20679	TP2781	452	Dimlington	Withernsea, Humberside

Bilby Towers were used also in the measuring of precise locations of the Radio telescopes at the Mullard Research establishment in Cambridge.