Pilkington & Gibbs Heliochronometer

[A.R Eden]

Pilkington and Gibbs Heliochronometers.   Yes, I am making a replica of the P & G Heliochronometer.  In fact I have been making it for about four years or more !   The trouble is that I have done all the easy bits, have been in and out of hospital a few times since I began and am rather stuck on the more difficult bits.   Though difficult to me, it would all no doubt be simple to an experienced metal worker and engineer.  I was, and remain, neither.   The Curator of Instruments at the Science Museum in London very kindly arranged for his technicians to dis-assemble their exhibition instrument, and allowed me to photograph and measure all the bits of it.   I  had never done such a thing before, and was not very good at it.   It lead to a number of repeat visits to the Museum each time my attempts to make computer drawings of the various components showed up contradictions in my measurements.   I also had to learn how to use a CAD program on a computer, which was time consuming.   The most difficult part was the design of the cam that is the key to the operation of the instrument, and which automatically corrects for the EOT.   I did not know what a cam was, let alone how to calculate its shape, but knowledgeable friends educated me, and the man who calculates the ephemera for the Nautical Almanac at the Royal Greenwich Observatory, Dr. Yallop, guided me as to the data needed to work out its profile.   I would be happy to make my calculations available to anyone who wants them, but I worked them out on a spreadsheet peculiar to the Acorn Archimedes computer I was using at that time, and am ignorant - and doubtful - as to whether I can copy the data / spreadsheets from the RISC system to a format readable on the universal PC. for others to read.        Only my completion of the instrument will tell if I got the calculations right, but I got the cam milled-out at the local Technical College on their CNC machine.  It looks right.  The college also allowed me to help them cast the bits that were best cast, and taught me how to us their big lathes for machining the bits that were too big for the lathe I was in the process of acquiring to do the rest.   It has all been great fun, and I have made a lot of sundial friends, not least the instrument makers at the science museum and Theo. van den Heiligenberg , in Holland, with whom I have corresponded ever since he decided to write a monograph on the Instrument (since published on the BSS Bulletin).    These instruments are not all that rare.   They come up at auction fairly regularly, so Sotherbys told me.   The original patent (No. 15,194 of AD 1911) describes the instrument and its working in detail, and has diagrams attached to it.   I got my copy from the Patent Office when it was in South Wales, and there was no problem there; the price was £2.86, inclusive of postage.   I understand that it is now much more difficult to get copies of patents since the Patent Office was moved to London, and I expect that copies are more expensive.      I have also seen the Pilkington & Gibbs sales brochure, probably dated just before or after the Great War, which priced the dials, in various sizes and various materials (gun metal, copper and "rustless iron") at prices ranging from eight to twelve guineas.   A glass dome to protect the instrument was an "extra" at two guineas.   (A guinea was one pound and one shilling, or £1.05, in modern decimal currency).   Their brochure also listed all the most famous purchasers of the dial, starting with the King !    I suspect that they were produced up to 1939, but not after the war.  There is one in the grounds of Greenwich Hospital, in need of much TLC, and |I know of one or two others in private hands.   The firm also produced a rather similar but ugly heliochronometer called a "Sol-Horometer"   It was designed by Pilkington (the Heliochronometer was designed by Gibbs, who was a professional engineer. Pilkington was the financial backer) and it lead to ill feeling between the two partners, as Gibbs thought that Pilkington had cribbed his work.   The Pilkington & Gibbs Heliochronometer should be accurate to a minute or so, when properly set up and adjusted.    I hope this note will be of interest to some, and apologise for the length of it.   Anthony Eden