Finding North America & Ferdinand Hassler's Chain 

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MapTack
Posts: 9

Joined: 10/11/2012
Topic  Finding North America & Ferdinand Hassler's Chain       Flag »  Reply »
Re: Richard Stachurski - <Longitude by Wire>

Part 1.....

Having only recently obtained this book I came across in Chapter 3/Station Head & Horns - "Constant pulling on the chain to straighten it lengthened the rings that connected the links.The links could be bent & shortened<<by being drawn over fences, rocks & other unyielding obstructions>>" "The crude tool produced crude results, a discrepancy of about 1:38000." The Common Land Chain probably gave a precision of 1:500 to 1:1000 for good work. The accuracy was even in doubt by surveyors particularly in the 16th & 17th C.

From research, the 20 metre chain with 1m links was made for Hassler by Edward Troughton and was of the same basic design as that used by William Bald in his baseline measurements for the triangulation of Co. Mayo in Ireland (giving up a precision if not accuracy of 1:127,000). This design by Troughton was to supply a chain capable of somewhat similar accuracy to the Ramsden Geodetic Chain made for Wm. Roy but considerably cheaper. This chain would not have been subject to the same drawbacks as the Common Land Chain. I presume that the Fire Island Baseline, since it was particularly selected as a site by Hassler, did not suffer from being drawn over fences, rocks &c and this reference is to the general failings of the Common Chain in such particular circumstances. It is interesting that the Troughton 20m chain did not number in the inventory of Hasslers' purchases when in Europe. I strongly suspect that Hassler may have purchased this at his own expense and did not have confidence in it as a tool for his purpose and thereby not declaring it in the inventory of purchases. Hassler's technical ambitions & exactitude are very similar to that of Thomas Colby of the Board of Ordnance in his compensating bars which were used to measure the Lough Foyle Baseline in N. Ireland. Colby had used the Ramsden Chain previously but went on to develop his baseline contrivance somewhat similar to that which Hassler eventually used. Adequate was alien to both proponents.

Hassler's "lack of confidence" would account for the earlier introduction of a secondary baseline. William Bald's response to not using trestled coffers but measuring along the ground with his great chain was to introduce more frequent baselines. The 1:38,000 is not a bad result particularly since Hassler may not have invested the effort in something in which he had little confidence. Although low by geodetic standards it would have been sufficient for small scale mapping particularly with additional baselines.


MapTack
  Saturday, October 13, 2012 at 8:10:47 AM
MapTack
Posts: 9

Joined: 10/11/2012
Reply  Re: Finding North America & Ferdinand Hassler's Chain Flag »  Reply »
Re: Richard Stachurski - <Longitude by Wire>

Part 2.....

 Colby could have sufficed with the scaled distances brought across the Irish Sea by Triangulation and perhaps made do with the Ramsden Chain for a check base in Ireland. Hassler too had used the Ramsden Chain in Switzerland prior to his emigration to North America. Hassler & Colby acting no doubt in the spirit of the Enlightenment were not prepared for anything but scientific perfection. I was unable to track down the A.M. Harrison report on the Plane-Table but presumably the chaining in this report refers to the common chain & not specifically to Troughton's chain for Hassler.

The Troughton design persisted into the 20th Century however as it found its specialist niche in acting as a Standard Chain and was known as Troughton's Standard Chain. This particular chain was used to standardise common working chains particularly within the Ordnance Survey but also with the British Inspectors of Weights & Measures. The chain in this form was made by Doyle & Son, London and by C.F.Casella, London no doubt among others. The Troughton pattern chain was also used in South Africa when neither the Ramsden chain nor the Colby Compensating Bars were available but the chain could be compared against previous measurements through triangulation taken with the foregoing devices. Froma general interest, both the Ramsden Chain & latterly Colby's Bars were used extensively in the GTS (Great Trig. Survey) of India - the Ramsden being also used a a Standard Chain prior to the availability of Colby's Bars.

MapTack
  Saturday, October 13, 2012 at 8:12:15 AM

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