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The invention of a ‘floating’ bubble device for determining or setting level surfaces is variously credited to Melchisédech Thévenot (France), Robert Hooke (England) and Vincenzo Viviani (Florence), in the 1660s. It’s use did not become widespread until the 1700s, and did not become the focus of sustained innovation until the latter half of the 19th century. During that period, hundreds of patents ‘improving’ this ostensibly simple device were filed.
The Stanley Rule and Level Company (in the person of the infamous Justus A Traut, who arrived in the US at age 14 in 1854, and filed over 300 patents, most of them for Stanley, before his death in 1908) was responsible for more than its share of these improvements.
Our focus today is on patent number 562,679, issued on June 23, 1896 to Mr Traut and his employee, Christian Bodmer (the US-born son of German immigrants whose name appears on at least 44 US patents). This patent was for a method of marking lines on the glass vials found in spirit levels, without weakening the glass in the way that inscribing a line into the surface would do. A thin disk of cast iron rotating at high speed would be brought into contact with the surface of the glass, and friction would heat both to the point where iron residue would fuse into the surface of the mark, leaving a visible black line. Glass vials with such markings were considered ‘proved’. Traut and Bodmer were also awarded a patent (No. 562,678) on the same date for the machine used in this process.
Today’s Toolporn Friday post features a rare complete, original wooden box of one dozen intact proved glass vials, packed in the original sawdust, dating from between 1896 and 1913. I acquired these intending to use them in period-authentic restorations of some of the many Stanley levels in the archive with broken vials – but I can’t bear the thought of breaking up the set, so they will enter the permanent collection