I've obtained this level in 2008. The instrument is probably of French origin, but is unsigned and nor is there any signature in the box. In the Netherlands the water bottle level was also referred to as waterwaag.¹

The instrument in this shape was first mentioned by Riccioli in a 1689 work by Philip de La Hire.² This level is as basic as a level can be; two communicating containers of water joined together with a brass tube (see figure 1 and figure 5). Water would be poured into the system, at times coloured using a dye.³ Visors floating on mercury were also used as a more accurate alternative.⁴

The surveyor would look along both bottles, trying to maintain a sight line along the water surfaces. Any object at the same height as that line would be level with it. The instrument can be mounted on the same tripod as the graphometer. In contrast to the hydrostatic level there are no scales on this instrument.

It is difficult to say something about the accuracy of this levelling system, but it may be clear that little accuracy may be expected from it. The use of floating visors may have improved on the quality of the observations, but came at an unhealthy price of using mercury.

The instrument came complete with a nice oak box (see figure 2 and figure 3). It has to be dismantled into five pieces in order to fit in it. To protect the hand blown glass bottles two additional parts are in the box; the brass tubular covers to protect the glass bottles when not in use. The tripod was acquired separately and most likely too is of French origin (both the instrument and tripod were bought in France).