The spirit of the age

While carrying out the inventory photography of the fabulous collection at Weaver’s Cottage in Kilbarchan, I came across two polished wooden boxes, roughly the size and shape of ice hockey pucks. Carefully removing one of the snug-fitting lids revealed a set of small blown glass bubbles. Each bubble has a unique number etched into the glass of the air-filled bulb. A solid glass rod on the opposite side acts as a weight for the base and serves as a handle with which to pick up the bubble.

The purpose of these objects quickly became apparent. A printed piece of paper inside the box states ‘Hydrostatical Glass Bubbles by James Corte, To prove spirits’. Also printed on the paper is a list of various alcoholic beverages, each next to a number. The numbers correspond to those etched onto the glass bubbles.

Opening the other box I noticed some differences in construction, although the bubbles appeared identical. The base of this box has holes in which to sit the bubbles, and the printed paper in the lid bears the simple instructions: ‘If the Spirits be Proof, the Bead will sink to the Bottom’ – which must be the shortest instruction manual ever! As with the previous set, the maker is named as James Corte, with the addition of his business address: Crawford’s Land, foot of Saltmarket, Glasgow.

Armed with this additional information of local interest, I decided to do some more research.

Surprisingly, the internet provided very little information. I discovered that hydrostatic bubbles are also known by other names, such as philosophical bubbles, specific gravity beads (the ‘Bead’ alluded to in the second set’s instructions) and, less commonly, aerometrical beads. At the time of writing, Wikipedia has no entries concerning this equipment, under any of these names. From the information I did find, it soon became apparent that I was dealing with a Glasgow story, and from a very short period of time.

Hydrostatic bubbles were invented by Dr Alexander Wilson (1714–86), a very talented man born in St Andrews, who became Professor of Practical Astronomy at the Glasgow College (later the University of Glasgow). It was there in the winter of 1757 that Wilson demonstrated his ability to measure very small differences in the specific gravity of similar liquids by using one of his blown glass beads and changing the temperature of the liquids tested. Applying this science to a practical use, it was realised that a set of calibrated glass bubbles matching various specific gravities of liquors would be a quick and convenient way of proving spirits. These bubbles were mostly used by spirit dealers, merchants and customs agents.

At the end of the 18th century there was a thriving scientific and mathematical instrument-making community in Glasgow. I can find no information about James Corte, but almost identical sets were made in Glasgow’s Trongate by James Brown, perhaps the first manufacturer. He died in 1789 but was succeeded by his apprentice, William Twaddell. Anthony Galletti, who began his career as a carver and gilder, also produced sets from his premises in Nelson Street, Glasgow. He and his sons became better known for optical instruments and spectacles.

Scientists throughout Europe at this time were experimenting with ways of measuring specific gravity, but the hydrostatic bubbles appear to have been a Glasgow phenomenon of the late 1700s. Although they were a very easy piece of equipment for merchants to carry, their period of use was relatively short as they were soon replaced by more accurate hydrometers.

Project Reveal is a Trust-wide collections digitisation project. It will result in an updated database with high-quality images and unique object numbers for every item in the National Trust for Scotland material culture collections. Six regionally based project teams, supported by experienced project managers, will work across all our properties with collections to complete the inventory in 18 months from July 2017 until December 2018.