While doing a bit of planimeter research, I noticed that Wikipedia gives the date of 11 November 1823 for Jakob Amsler-Laffon’s birthday – 200 years ago today! Amsler was a Swiss professor of mathematics, best known for his 1854 invention of the polar planimeter, an area-measuring instrument of beautiful simplicity that was to become the dominant form for more than a century.
However, as ever with Amsler, nothing is as straightforward as it seems. As a formality, I attempted to track down some corroborating sources (preferably contemporary) for Amsler’s birth date. While the Historisches Lexicon der Schweiz (HLS) and German language version of Wikipedia both agree with the 11 November date, other online sources including Deutsche Biographie and Stadtarchiv Schaffhausen (cached page, original currently offline) give a different date, the 16th of November 1823.
In print, the latter date is backed up by the Dictionary of Scientific Biography and Julius Gysel’s 1957 article from Schaffhauser Beiträge zur vaterländischen Geschichte. Going back further still, most of the sources published during Jakob Amsler’s lifetime or or upon his death in 1912 agree with the 16 November birth date (see, for example, the E-Periodica scans here, here and here). Unfortunately I have not been able to locate any genealogical sources, Switzerland’s church records of the time being rather patchy and largely uncatalogued.
It would therefore seem that the 11 November date crept in erroneously, perhaps with the HLS, and has since been propagated across the web from the Wikipedia entry. Ironically, the first reference on the English language Wikipedia page is to the Dictionary of Scientific Biography, which got the date right!
Therefore, in celebration of the (almost) bicentenary of Amsler’s birth, I thought it would be fun to post a few planimeter-related items over the following days. It seems somehow appropriate that today’s example is also not quite what it seems.
At first glance it is a fairly unremarkable Type 6, with the characteristic spikes on top of the tracer arm that were specifically intended for the measurement of engine indicator diagrams.
However, some of the details are unusual, particularly the removable covers for the two spikes which are very finely engineered with knurled “mushroom” tops, presumably to facilitate their removal.
The proportions of the planimeter itself are also not quite those of an Amsler, especially given the serial number 5277 which would place it towards the late 1860s in Amsler’s sequence.
Moreover, the box is not the usual Amsler design, as it has a push-button catch and tooled leatherette covering (although some of the very earliest Amslers did come in push-button cases).
At this point, my thoughts would usually turn to alternative makers, such as Blankenburg or Dennert & Pape (the former of which definitely used push-button cases for a time), but on this occasion nothing seems to fit. The typeface of the serial number is unlike any other Blankenburg example I have seen. On the other hand, none of the usual D&P features such as the curved index window or elaborate tracer point are present. Both the Vernier wheel and indicator of my example are made of white celluloid, which suggests a later date, at least on the basis of Amsler’s chronology.
For now, this planimeter remains an outlier, a not-quite-Amsler for Amsler’s not-quite-birthday. Any ideas or suggestions as to its maker would be most welcome.