Orwell Astronomical Society (Ipswich)
The Reverend Edward Lyon Berthon MA, FRAS (1813-99)
Edward Lyon Berthon was born in Finsbury Square, London on 20 February 1813, the tenth child of Peter Berthon, who ran a business supplying the Army with provisions. The end of the Napoleonic Wars in 1815 reduced the family income and, as a result, at the age of five years, Edward was adopted by his grandmother. She sent him to private schools in east London up to the age of fourteen years. After that, he was sent to Liverpool to study surgery so that he could take on the practice of his maternal grandfather, Henry Park, after the latter's retirement. Edward was fascinated by mechanical engineering and attended the Rainhill Trials to see George Stephenson’s Rocket. He was very inventive and eventually held 25 patents.
Marriage to Margaret Preston of Toxteth, on 04 June 1834, put an end to Berthon's medical career. The pair embarked on a tour of France, Switzerland and Italy that was to last six years. Eventually, they produced two sons and five daughters. While in Geneva, on 28 June 1834, Berthon devised a screw propeller for marine propulsion but was so discouraged by those around him that he abandoned it. A mere twenty years later, during the Crimean War, the majority of ships in the British Navy were using screw propulsion in place of paddle wheels, much to his chagrin. He was given to flashes of inspiration and on one occasion started to hurriedly chalk a design for a "sea anchor" on the back of a church vestry door, much to the amazement of the choir!
Back in the UK, in 1841, he entered Magdalene College, Cambridge to study for the clergy. Graduating as BA in 1845 and MA in 1849, he moved to Hampshire where he was first given the curacy at Lymington and then the living of Fareham (1847-57). Being on the coast he was able to indulge his passion for nautical invention with further work on the screw propeller, a navigation log and, in 1849, the "Berthon Folding Boat". He exhibited the latter two at the Great Exhibition in London in 1851. The log was rejected by the Navy on the grounds that it was too delicate for service use, although one was fitted to the new royal yacht Victoria and Albert. The folding boat was also rejected.
In order to escape maritime matters, in 1860 Berthon moved to Romsey, where he remained until his retirement in 1891. His engineering talents were put to good use devising machinery to restore the fabric of Romsey Abbey Church. In 1873, Samuel Plimsoll encouraged Berthon to examine again the idea of his "Folding Boat"; this time the idea was adopted by governments at home and abroad and orders to the value of £15,000 were placed. A boatyard was acquired and, at the height of the business, over one hundred workmen were employed: it is still in business nowadays. During 1881-82, Berthon travelled to Cape Town to thoroughly test some of his nautical inventions. He followed this in 1885 by a trip to New York to promote the sale of his boats but found that American import duty made sales uneconomic.
In his free time, Berthon constructed equatorial reflecting telescopes, that is everything except the mirrors. At the Paris Exhibition in 1878 he received a silver medal for an instrument of 32 cm aperture. A year before his death he completed a 42 cm, three metre focal length telescope complete with observatory. The instrument, which was for export to South Africa, was constructed at his boatyard and Sir Howard Grubb supplied the optics. Many of his telescopes were supplied to other priests, for example the Reverend Thomas William Webb (1807-85), the well-known astronomer and author of the classic work "Celestial Objects for Common Telescopes".
Berthon was elected a fellow of the Royal Astronomical Society on 08 January 1865. He read only one paper to a meeting of the Society, on 11 December 1874, entitled On the Equestrian Equatorial. At the meeting, he demonstrated a model of the mount. Presumably the name of the mount derived from the double counterweights, looking rather like rider's legs on either side of a horse.
Berthon wrote his autobiography, A Retrospect of Eight Decades, shortly before his death at Romsey on 27 October 1899.
This was the name given to the "standard" small amateur astronomical observatory of the late nineteenth century. The original model was built by Berthon while at Romsey, in 1863. It consisted of a small circular equatorial room with conical roof and adjoining rectangular transit room. The exact dimensions of the observatory were dictated by the size of the telescopes and the site available. Berthon was able to use his boatyard facilities to manufacture these observatories.
Berthon is perhaps best remembered nowadays in the amateur astronomical community for his "dynamometer". This device is used to measure the diameter of the pencil of light rays emerging from the eyepiece of a telescope. In Berthon’s day this bright circle was known as the "Ramsden Disc"; the modern term is "exit pupil".
The magnifying power of a telescope/eyepiece combination is simply the diameter of the objective divided by the diameter of the exit pupil. Berthon published details of his dynamometer in The Engineer on 15 September 1871. Being somewhat outside his usual product range of telescope mounts and boats, he procured the services of a local watchmaker, a Mr Tuck, to manufacture dynamometers on his behalf and sell them for five shillings each.
A good dynamometer will measure the diameter of the exit pupil of a telescope to an accuracy better than 0.1 mm so, clearly, an ordinary ruler will not suffice. Berthon’s solution was to use a form of "diagonal scale"; he constructed a piece of brass sheeting with a narrow isosceles triangular aperture of around 40 mm long by 6 mm base. A scale was graduated along one of the longer sides from zero to 6 mm. The sheet is simply held against the eyepiece and slid back and forth until the edges of the opening just impinge on the edges of the exit pupil. This operation should be carried out looking into the telescope with the observer's eye around 30 cm from the eyepiece. A magnifying glass can be used to assist if required. Varying the level of light falling on the scale from over the observer's shoulder can also be helpful.
In fact, Berthon's dynamometer doesn’t measure the diameter of the exit pupil, but a chord close to it; this is because the sides of the aperture aren’t parallel.
Bill Barton, FRAS