As part of a large cataloguing project to research all the NMM’s marine chronometers, I am currenmtly undertaking a close study of Harrison‘s third marine timekeeper, H3 (made during the 1740s). It is proving hugely interesting and revealing as can be seen in the videos which have been tracking my progress.
The aspect I’m studying at the moment is the extraordinary (at least to me) glazed brass case of the instrument, and I’m wondering about 18th century ‘instrumental’ practice where glazed cases are concerned? The case (which the timekeeper fits in very closely indeed and which stands just over 60cms high) has a ‘top’, a middle band (attached to the timekeeper) and a ‘bottom’, the three parts held together round the middle with 32 screws. The whole thing is incredibly beautifully made, using cabinet-making techniques, and consists of precisely 501 parts, all fitted together mechanically, with no solder anywhere. The brass panels are just 2mm thick and the four main vertical edges are dovetailed (yes!) all the way from top to bottom with a total of 174 tiny dovetails rather in the way that coppersmiths tie plates together before soldering, but much finer and without solder. The dovetails are so well cut the vast majority cannot be seen, but I show a patch where corrosion and stress has revealed some of them (I have temporarily marked the lacquered surface with felt-tip pen to identify them).
The brass panels with dovetails
The structure inside forming the frames for the glazed panels are all pinned and riveted with 425 rivets, and the glass is then puttied in. The decorative moulded cornice is also ‘invisibly’ attached all round with pins, disclosed at one corner where the case was damaged in the past and was apparently heated to repair it, not very successfully.
The decorative moulded cornice
I wonder whether such large cases are unusual at this period, or are other instruments made in the mid-18th century that are housed in such cases? If so, how are they constructed? I am familiar with the 18th century grand orreries (e.g. those by Wright etc) in the lovely ‘cold-frame’ type wooden glazed covers, but can’t think of anything in metal at this period. If anyone knows of any examples please do get in touch below.
The annual Lyrid meteor shower is visible from about 16-25 April and this year peaks 21-22 April. Unfortunately this year the glare of a waning gibbous moon will spoil the view in the late night and early morning hours, which are usually the best time to catch the Lyrids.
The Lyrids are a reliable annual shower of bright fast meteors, some with trains, associated with the periodic Comet Thatcher. The Lyrids are so called because the shower’s ‘radiant’ (the point from which meteor trails appear to radiate) is in the constellation of Lyra, in the north-eastern sky as seen from the UK.
Most Lyrid meteors are around magnitude +2 but some, known as ‘Lyrid fireballs’, are much brighter and cast shadows for an instant, leaving behind smoky trails of debris that can last several minutes.
The Lyrids are not generally among the most spectacular showers, and usually only produce between 5-20 meteors per hour. However, occasionally the Earth
passes through a thicker part of the comet’s dust stream resulting in a more intense shower or ‘meteor storm’. In 1982 amateur astronomers counted 90 Lyrid meteors per hour, and in 1803 an even stronger storm was observed.
The Lyrids were also observed as far back as 687 BC as recorded in the Chinese ‘Zuo Zhuan’ or Chronicle of Zuo, making them the earliest-known meteor shower.
The next major annual shower is the Eta Aquarids, associated with Comet Halley. These are generally visible from around 24 April until 20 May, with a peak around 5 May when you can hope to see up to 35 meteors per hour.
This year the Royal Observatory will be taking part in Obscura Day, an international ”day of expeditions, back-room tours and hidden treasures” developed by the people behind Atlas Obscura. On Saturday 9 April there will be two different curator-led tours on offer. Further details can be found on the NMM events list (here) and should be booked on the Obscura Day website (here - put ‘Greenwich’ in the search box). Because both tours will include a visit to the object stores of Flamsteed House, numbers are limited – book your place now!
Tour 1: 10.30: Go back in time at the Royal Observatory Greenwich Take a tour back in time with Dr Rebekah Higgitt, Curator of History of Science and Technology, through the astronomy, buildings and collections of the Royal Observatory. Learn to tell your altazimuth from your equatorial, spotting Victorian terracotta and Tudor vaults on the way.
Tour 2: 13.00: Charting Greenwich Mean Time Come to the Prime Meridian of the World and explore the collections at the Royal Observatory, Greenwich with Rory McEvoy, Curator of Horology. Discover how Greenwich Mean Time was determined and kept throughout the years and why an observatory should be so closely connected with precision timekeeping. The tour will include a rare opportunity to see some unusual time related objects from the Museum’s reserve collection
Meeting place for tours: Shepherd’s Gate Clock, main gate, Royal Observatory. Tours start promptly. Please arrive at least 5 minutes before start.
1 April 2011 – In the early hours of this morning, top ROG astronomer Firla Pool made a chance discovery while observing that could potentially reshape our understanding of alien life.
Making observations late into the night at the ROG’s famous 17¾-inch telescope, Ms Pool stopped by the astronomers’ refrigerator for a sustaining snack. On opening the door, she was amazed to be met by an array of colourful, pulsating lifeforms which had apparently evolved super-rapidly on an abandoned pot of pro-biotic yogurt, several years over its use-by date. Ms Pool was convinced that the lifeforms were trying to communicate with her, and claims she distinctly heard a voice saying “Take me to your larder”, though she later admitted that she may have been mistaken as she was rather tired.
Unfortunately, when an excited team of scientists and journalists arrived at the Observatory this morning, they discovered that the cleaner had got there first and had decontaminated the whole area. “I don’t know when that fridge was last cleaned,” confessed the cleaner, Miss Tayke. “We tend to avoid it as the astronomers keep Moon cheese in there, and it can get very smelly.”
Coincidentally, a member of the cleaning team was also involved in a surprise astronomical discovery on exactly the same date last year.
