'Brass and glass' in the context of this site is usually associated with the many makers and models of pre-20th century microscopes where the finish was typically lacquered brass. My brother Ian and I over the years have been custodians of a variety and have often shared our experiences of them. A limited budget and space has always kept this collection to three or four at most. We enjoy using and researching their history and after a few years, resell to release the budget for new explorations.

We pride ourselves on always passing them on in better condition than when acquired. We have lost count of examples that from their state seemed to have been passed through a cycle of owner and/or dealer with no attempt to bring to working condition (this also applies to old slides where it seems to be the norm—dirty and forgotten).

Another of our joint interests is the many aspects of the history of exploration, navigation and timekeeping—whether old maps, atlases, reading the exploits of explorers etc. In my case I have a particular interest in the quest for the North West Passage. As a new avenue for a collection of 'brass and glass' over the past few years we have bought where affordable examples associated with these interests to enjoy and research. In this article we share our two pocket sundials, in part 2 our three sextants, one pocket and two full sized.

Pocket sundials would of course have had no value in navigation where very accurate chronometers developed by John Harrison and others in the 18th century were required for measuring longitude. Pocket sundials were likely typically owned by the more wealthy. The two owned contrast in their sophistication. They are appealing collectibles because it prompts research into factors such as the equation of time and magnetic declination as well as the maker if known.

Pocket sundial with magnetic hour dial in fruit wood case ca. 1840s?

This smaller model measuring just 57 mm at base with a dial ca. 38 mm is likely made of a fruit wood like pear with a closely fitting lid. It is not of course 'brass and glass' but is a useful comparison to the larger model below. The angle of the gnomon (the feature that casts the shadow) is ca. 50 - 60° suggesting it was British made. The British Sundial Society via their 'Help and Advice' contact were very helpful in providing an insight into their construction. I thought the gnomon was the magnet but typically there's a magnet beneath the dial. The dial also needs to be balanced underneath with tiny drops of wax to ensure level in the locale of use to correct for local magnetic dip. The glass dome does rub if not held exactly level. The base may have a label but has worn off, typically equation of time corrections for a fixed gnomon. For such a thin gnomon there is no correction for shadow thickness on the dial, the middle of the shadow is read, unlike the sundial below. These designs do not seem robust enough for the rough and tumble of being pocketed.

A puzzle is why this sundial gives within its limits of accuracy (ca. 15 mins) the correct time after adjusting if necessary for the current 'equation of time' (how time using the sun's shadow differs from local standard time). Sundials are only fast by 53 seconds at time of writing (June 9th), see this real time calculator so not a significant correction in early June. On November 12th this year, if lucky enough to have sunshine, the sundial would be reading 16 mins fast. In 1840 in the UK the magnetic declination (difference between magnetic and true north) was ca. 25°, the NOAA website has a valuable interactive map with timeline to calculate this. This suggests the sundial should be over an hour out as the current local declination is zero. It may have been adjusted later in its life although no evidence of modification so perhaps incorrectly set when new. Parts of the US had near zero declination in ca. 1840 but the angle of the gnomon to suit these latitudes would have been closer to 40°.

Image right, crop of the map of declination 1819 with isogonic line closest to Huddersfield in N. England highlighted to give 26° West of North declination. Source NOAA website.

Pocket sundial ca. 1840, magnetic dial.

Pocket sundial with base compass, brass in fitted box, T. Rubergall at 1805 - 1822 address.

This pocket sundial in its fitted box is more sophisticated (size 10.5 x 10 x 4.2 cm). It is inscribed T Rubergall OPTN to his RH [Royal Highness] Duke of Clarence 27 Coventry St LONDON. Thomas Rubergall from Gloria Clifton's invaluable 'Directory of British Scientific Instrument Makers' (1995, 1996 reprint, National Maritime Museum / Zwemmer) was working at this address between 1805 - 1822 and was a London worker between 1800 - 1854. A maker to be awarded a royal appointment was quite an accolade. The Duke of Clarence became William IV in 1830 where his royal appointment continued and later to Queen Victoria. The entry states 'Known to have sold: chondrometer, microscope', the former measures the bulk density of grain (Wikipedia entry with illustration). The antiques-microscopes.com website shows a well made Cary-Gould style microscope by Rubergall. A compound microscope and small simple microscope, the latter in a leather case also documented. A telescope with his name is also documented online.

To supply goods to the royal family suggests a maker who has built up a reputation for making the highest quality instruments and such appointments continue to this day for a wide variety of products. Unlike the smaller sundial where setting north is automatic, a splendidly engraved compass is set in the base, it has a lever lock for the needle during transit. The clock dial can be set for local latitude between 0 - 60°. The gnomon and the angle arm both fold flat to fit in the mahogany box with clasp fitting and velvet lined lid. This sundial has thick gnomon and a gap in the engraved hours can be seen at XII to account for this. The side of the shadow read changes at midday.

The brass base plate has latitudes to set on the arm provided for a rather eclectic group of British mainland cities, London, Glasgow, Exeter, Oxford and overseas, Paris, Lisbon, Dublin, Moscow.

Sundial by T. Rubergall

Both sundials at 1102 UTC giving the correct time. The lefthand one should not be correct if adjusted for the declination at the time it was made. Magnetic north is the same as true north in Huddersfield at time of writing. The arm has been set for the local latitude of 53.6°N. The equation of time correction in June is less than a minute and local magnetic declination is zero so corrections for neither are needed. The compasses have been closely grouped for the convenience of a single photo but would not be used close together as there is slight interaction.

Comments to the author David Walker are welcomed.

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