Latitude Stations from the 1850s

[Papa-Bear-NYC]

Latitude Stones

 

Many of the primary EOA stations were also sites where astronomic latitude (and occasionally longitude) was measured. Longitude is difficult, especially in the 1840s and 1850s since they needed to measure a time difference between the station from a known point. Until the use of telegraphic measurements became more commonplace a decade or so later, this was rarely attempted, and inaccurate when done.

 

Latitude was relatively easier to measure: just measure the inclination of a known object (the sun, various stars, etc.) when it crosses the meridian and bingo! you've got your latitude.

 

Unlike the sailor pictured on the deck of a ship with a sextant, a highly accurate zenith telescope was used, since it was important to get readings to a fraction of a second.

 

The locations of the latitude stations and short descriptions are given in CGS Special Publication No. 110 "Astronomic Determinations" (1925), which is available on line: CGS Special Publications. This gives in depth discussions of methods and photos of early instruments, but unfortunately nothing showing their use in the field.

 

Harold Nelson, Senior Geodesist for the Maine DOT, who is a history buff on early surveying techniques, sent a link for the Zenith Telescope (also pictured in the above publication), the instrument used at the time: Zenith Telescope

 

Zenith Telescope at the Smithsonian National Museum of American History

 

These instruments were mounted on stone platforms or posts set near the triangulation station. Unfortunately I have not been abler to find any pictures, sketches or even verbal descriptions of these stones on the net, but Harold sent a plan for the Farmington Observatory (at the University of Maine at Farmington), in which the stone is shown as a post with a triangular cross section.

 

Farmington Observatory floor plan and elevation

 

Both MT HARRIS and RAGGED MTN were known to have done latitude measurements and in both cases I found stones about 4 feet long lying on their sides near the appropriate location (typically 10 to 20 yards from the station). The HARRIS stone is rectangular in cross section and the RAGGED stone is triangular. Harold saw my photos and is excited by the finds and feels that these are very likely to be the latitude stones used in the early surveys.

 

MT HARRIS Stone

 

RAGGED MTN Stone

 

Here are links to my GC logs which have this text plus additional photos:

 

MT HARRIS Latitude Stone Log

RAGGED MTN Latitude Stone Log

 

If there's anyone out there with more information on these old artifacts, please chime in.

Edited August 22, 2008 by Papa-Bear-NYC

[DaveD]

You can find descriptions of astronomic stations observed by the Coast & Geodetic Survey and other agencies in Special Publication 110 "Astronomic Determinations."

[+GEO*Trailblazer 1]

Man are you fasr DaveD.

 

Here is a clip from here:

NOAA History

 

Station Monuments

 

Lasting station monuments, for obvious reasons, were always of fundamental importance in geodetic surveys. Where rock ledges or large boulders were available, Hassler utilized drill holes filled with sulphur or some other substance to reduce the effects of freezing. Elsewhere, buried truncated earthenware cones were the rule. The center of the smaller radius end marking the exact station. Sub-surface (underground) marks also were usually set in the same fashion. In most cases, at least one reference (witness) mark was established, drill holes and cross cuts in rock structures and truncated earthenware cones, smaller than the station marks were standard. Hassler buried the reference cones in a specific pattern, providing visible reference information to locate the general station site, and in addition buried small pieces of rubble, sea shells and the like found at the site, atop the station mark to aid in the recovery.

 

Reference marks serve several purposes: To aid in locating the station, to verify its position, to reset the monument and for use as substitute stations.

 

Versatile Concrete

 

Base line stations were usually marked by heavy stone posts until about 1900 when poured concrete monuments replaced them. From about 1850 to the turn of the century, stone posts (marble, sandstone and limestone) 2-3 ft. in length, and for sub-surface marks the same type of posts, bottles, earthenware jugs and crocks and similar, generally replaced cones for marking stations. However, in some instances, bolts and nails cemented in drill holes, simple drill holes, cross cuts and in fact, almost any conceivable mark, in any combination with these station markings were utilized. When necessary to bury the marks, a ditch 4-8 ft. in diameter and 8-18 in. deep, surrounding the station location was usually dug and filled with coal or charcoal. Once concrete became readily available, 2-3 ft. long tile and tin pipes filled with the substance, set over underground marks were often employed with centers marked by bolts, nails, punch holes, etc.

[Papa-Bear-NYC]

You can find descriptions of astronomic stations observed by the Coast & Geodetic Survey and other agencies in Special Publication 110 "Astronomic Determinations."

Thanks Dave.

 

I have that publication and I mentioned it above. But there are no details of what was actually in place on the ground in this early era. Remember Special Pub. 110 was published in 1925, almost 75 years after these early surveys. The best I have is the sketch of the Farmington Observatory which I included above.

 

There is incidentally another Special Publication, No. 13 (first published in 1913) which shows some Latitude stations (one within sight of the U.S. Capitol Building). But by that time they set the instruments on wooden or concrete platforms.

Edited August 22, 2008 by Papa-Bear-NYC