{"id":1193,"date":"2024-08-31T14:11:28","date_gmt":"2024-08-31T14:11:28","guid":{"rendered":"https:\/\/graphography.org\/?p=1193"},"modified":"2024-09-23T09:43:44","modified_gmt":"2024-09-23T09:43:44","slug":"ogles-aphemetric-compass-a-mystery-solved","status":"publish","type":"post","link":"https:\/\/graphography.org\/index.php\/2024\/08\/31\/ogles-aphemetric-compass-a-mystery-solved\/","title":{"rendered":"Ogle’s aphemetric compass: a mystery solved"},"content":{"rendered":"\n

A huge thanks to Robert Pilla of the Drawing Instruments<\/a> group for helping me solve the mystery of my Elliott Bros dial dividers<\/a> posted back in January. His reference to Carroll’s Aesthesiometer of 1871 – a medical device for measuring the tactile sensitivity of skin – led me to this comprehensive paper<\/a> by Serge Nicolas and Dalibor Vobo\u0159il in L\u2019Ann\u00e9e psychologique<\/em> 2019\/1 Vol. 119 (illustrated PDF here<\/a>) which happened to include a drawing of “Ogle\u2019s aphemetric compass” made by the firm of Frederick Henry Elliott and Charles Alfred Elliott – clearly the same instrument as my mystery dial dividers. Far from my previous remark about those sharp points not being something a conscious patient would want to come into contact with, it turns out that this was precisely the intention!<\/p>\n\n\n\n

First described by Dr John W Ogle in his 1859 article<\/a> “The Aphemetric compass, an instrument for measuring the degree of discriminating power as regards contactile impressions, enjoyed by the skin and mucous membranes in certain affections of the nervous system”, it was intended to simplify the operation of earlier aesthesiometer designs by the addition of a direct reading scale, while also allowing one-handed use.<\/p>\n\n\n\n

\"John<\/a><\/figure>\n\n\n\n

The test was originally conceived in the late 1820s by German doctor Ernst Heinrich Weber, who published the pioneering work on the subject in 1834. It was intended to measure two-point discrimination<\/a>, the phenomenon by which two points applied to the skin close enough together are felt as a single point. By finding the shortest distance at which two points can be detected – the patient’s “two-point threshold” – the test could be used to diagnose neurological impairment due to nerve damage.<\/p>\n\n\n\n

Weber’s first instrument was nothing more than a plain Stangenzirkel<\/em> (beam compass), although he is said to have later abandoned this in preference for “the steel compass of ordinary mathematical use, blunted at the points”, as recounted in Ogle’s article. However, the term “aesthesiometer” was only coined in 1858<\/a> by Dr Sieveking, just one year before Ogle published his aphemetric compass. Sieveking’s instrument was a simple modification of Weber’s beam compass, by the addition of a divided scale on the face of the beam. The Science Museum has what appears to be an early example<\/a> made by FE Becker of London in their collection.<\/p>\n\n\n\n

\"Sieveking's<\/a><\/figure>\n\n\n\n

Ogle refers to Sieveking’s aesthesiometer in his paper, which suggests that the 1858 publication had been the immediate catalyst for his own design. Ultimately, however, he credited the idea to Weber’s “steel compass”, of which “my aphemetric compass is a modification”.<\/p>\n\n\n\n

Elliott Bros seem to have become involved in the design of Ogle’s aphemetric compass at a relatively early stage. For example, due to the non-linear ratio of the angle subtended by the compass legs and the linear distance between their points, the dial had to be specially calibrated – a fact alluded to by Dr Ogle in a footnote:<\/p>\n\n\n\n

\n

It was made for me by the well known firm of Messrs. Elliott and Co., instrument makers, Charing Cross, London, whose foreman Mr. Becker, after learning the principle on which I desired the instrument to be constructed, supplied all the calculations, &c., involved in the delicate graduation of the dial-plate, &c.<\/p>\n<\/blockquote>\n\n\n\n

Bizarrely, the finished article did not fully meet the requirements of an aesthesiometer, an oversight admitted by its inventor:<\/p>\n\n\n\n

\n

I must allow that, as regards its application, the instrument which I had made does not quite possess sufficient range of measuring power, as it is not quite able to measure five inches of the surface; but of course this defect is easily remedied in future instruments of the kind.<\/p>\n<\/blockquote>\n\n\n\n

This was possibly the outcome of Ogle having taken his cue from Sieveking’s published design which, like the Science Museum’s example, only measured up to four inches.<\/p>\n\n\n\n

\"Illustration<\/a><\/figure>\n\n\n\n

It will be noticed that the illustration of Ogle’s compass from his article has a dial reading to five inches, indicating that it was prepared after Elliott’s initial production and therefore one of the “future instruments of the kind” which its author envisaged.<\/p>\n\n\n\n

Even so, Elliott Bros were clearly still selling Ogle’s original four-inch aphemetric compass several years later, as the case marking of my example gives the address 449 Strand, occupied by the firm from 1864. Perhaps Elliott had produced an initial run of compasses that remained to be sold, but it may equally reflect a deft bit of post-rationalisation on Ogle’s part, who optimistically observed that:<\/p>\n\n\n\n

\n

This instrument obtains favour also, I was glad to find, with others than physiologists and physicians. One skilled in mechanics and mathematical appliances spoke in a highly favourable way of its future use for quickly and accurately reducing geometrical distances in the construction of plans, engineering diagrams, &c.; and of its serving, in a superior manner, the purpose of the calipers in ordinary use.<\/p>\n<\/blockquote>\n\n\n\n

Ogle even set out a proposed modification of the original design, suggesting:<\/p>\n\n\n\n

\n

Perhaps, if the limbs of the compass were somewhat arched, this intention of geometrical mensuration would, by making it useful in the case of solid bodies, &c, render it still more generally applicable.<\/p>\n<\/blockquote>\n\n\n\n

This brings to mind the closely related instrument<\/a> in the Science Museum, London, which features both arched limbs and an increased range compared to the 1859 aphemetric compass design. However, the 56 Strand address on the case would place its manufacture between 1854 and 1857, suggesting it may be an earlier model – was Dr Ogle responsible for this instrument as well?<\/p>\n","protected":false},"excerpt":{"rendered":"

A huge thanks to Robert Pilla of the Drawing Instruments group for helping me solve the mystery of my Elliott Bros dial dividers posted back in January. His reference to Carroll’s Aesthesiometer of 1871 – a medical device for measuring the tactile sensitivity of skin – led me to this comprehensive paper by Serge Nicolas […]<\/p>\n","protected":false},"author":1,"featured_media":1205,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[227],"tags":[37,290,286,243,7,242,234,235,126,249,287,288,289],"class_list":["post-1193","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-dividers","tag-19th-century","tag-aesthesiometer","tag-aphemetric","tag-bros","tag-compass","tag-dial","tag-elliott","tag-elliott-brothers","tag-england","tag-medical","tag-ogle","tag-sieveking","tag-weber","entry","has-media"],"_links":{"self":[{"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/posts\/1193","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/comments?post=1193"}],"version-history":[{"count":12,"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/posts\/1193\/revisions"}],"predecessor-version":[{"id":1215,"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/posts\/1193\/revisions\/1215"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/media\/1205"}],"wp:attachment":[{"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/media?parent=1193"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/categories?post=1193"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/graphography.org\/index.php\/wp-json\/wp\/v2\/tags?post=1193"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}