I am having a discussion with my client about magnetic declination. We searched the Internet and found this Gurley compass that has a vernier for adjusting the magnetic declination. I had never heard of such a thing and always assumed that surveyors' compasses measured magnetic north.
http://www.earlycorvettes.com/budinstruments/fdugurleymidsize.htm
Historic boundaries and conservation efforts.
Search Beerleg for Warren Knight Model 130 Sipe-Sumner Pattern Staff Compass...a production vernier compass
DDSM
not my real name, post: 336987, member: 8199 wrote: I am having a discussion with my client about magnetic declination. We searched the Internet and found this Gurley compass that has a vernier for adjusting the magnetic declination. I had never heard of such a thing and always assumed that surveyors' compasses measured magnetic north.
http://www.earlycorvettes.com/budinstruments/fdugurleymidsize.htm
Not to nit pick, but ANY compass, surveyor's or otherwise, is intended to, and does "measure" magnetic north at the location it's at, subject to local impacts on the device (metal, magnets, etc.). The "declination vernier" may just be an adjustment to turn the scale to the local declination, so that the unit "points" to true north?
not my real name, post: 336987, member: 8199 wrote: I am having a discussion with my client about magnetic declination. We searched the Internet and found this Gurley compass that has a vernier for adjusting the magnetic declination. I had never heard of such a thing and always assumed that surveyors' compasses measured magnetic north.
http://www.earlycorvettes.com/budinstruments/fdugurleymidsize.htm
What did you expect from the early corvettes page? Expert information on surveying equipment?
I have a K+E staff compass and a Dietzgen engineers transit, both have a vernier that allows the scale to be rotated the declination angle east or west.
The vernier is mainly intended to allow you to set a declination that will let the needle point true north in your area.
GLO surveyors of the early-middle 1800's running the section lines used the vernier to fudge their direction as needed, essentially re-estimating declination from prior misclosures.
Thank you for the responses. I too have a compasses that allow for adjustment of the declination. My assumption was that the colonial surveyors' compasses circa 1700 did not.
The concept of magnetic declination was known in early times. Europeans began to make systematic measurements of declination in the early 1500, and the Chinese had done it much earlier.
Historic boundaries and conservation efforts.
vern, post: 337013, member: 3436 wrote: What did you expect from the early corvettes page? Expert information on surveying equipment?
Although I do not see how it is made from the "earlycorvettes" homepage, the link to the compass is not that surprising. This website belongs to the son of Francois ÛÏBudÛ Uzes, who was a noted California surveyor, author and collector of such instruments. While some may disagree, he was probably the preeminent authority on antique surveying at his death in 2006, if not ever. A memorial to him may be found at www.mdshs.org.
That is an interesting story about Bud. He was a great man. Thank you LRWells.
Historic boundaries and conservation efforts.
not my real name, post: 336987, member: 8199 wrote: I am having a discussion with my client about magnetic declination. We searched the Internet and found this Gurley compass that has a vernier for adjusting the magnetic declination. I had never heard of such a thing and always assumed that surveyors' compasses measured magnetic north.
http://www.earlycorvettes.com/budinstruments/fdugurleymidsize.htm
Gurley made many different types of vernier compasses. The main purpose of the "vernier" adjustment was not for correcting magnetic declination but to set your compass to match an existing bearing on a line you were retracing, or so they say in their manual.
On a side note the Surveyors Historical Society will be holding their 2016 Rendezvous in Lake George N.Y. where among learning about Verplanck Colvin there will be a special presentation on all things Gurley and the William Smart Collection by the NYS Museum and Bill Skerritt.
Jim
James Vianna, post: 337121, member: 120 wrote: On a side note the Surveyors Historical Society will be holding their 2016 Rendezvous in Lake George....
We getting a discount conference rate at The Sagamore? 😀
James Fleming, post: 337128, member: 136 wrote: We getting a discount conference rate at The Sagamore? 😀
That's a good one, ha ha, Actually we will be staying at the Fort William Henry Hotel and Convention Center. Our lunch cruise however passes in front of the Sagamore though