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Any light on this?

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Many triangulation station data sheets mention a light above the station mark. It makes me wonder if the observations were typically done at night. It is a romantic image - a surveyor perched on a darkened hilltop squinting through his theodolite at a ghostly point of light hovering above a distant peak. But is that really the way it was done?


More generally, are there any readable descriptions of what a typical day in the life of a 1930s era CGS surveyor was like? What was the size of a typical team, what were the backgrounds of its members, and how long did it normally take to set a new station? It would be a fascinating read.

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They took the sightings at night because of more stable air, avoiding heat waves. They were sighting 10 miles or more at times, so visibility was a major concern. Another reason was that heat from the sun would cause some expansion of one side and move the instrument.


There are some historical pictures of the work somewhere on the NGS web site.


Also search this site for posts having to do with Bilby towers, which were double (inside and outside) towers designed by Jasper Bilby to to be easy for a crew to put up and take down. The crew was on the outer tower and the instrument on the inner tower so they didn't shake it.


I went to the dedication (2014) of the Bilby tower installed in his home town of Osgood, Indiana by the Surveyors Historical Society with the help of others. This tower was either the last known to exist, or perhaps there is one other. It was located because of discussion on this forum, which I passed on to the SHS.

Salvage operation pix

Rebuilding pix

Dedication ceremony pix including links to more info. A State of Indiana historical plaque in Osgood will be dedicated November 5, 2016.


There were former members of tower crews in attendance at the dedication, who probably did that work as late as the 1970's. They reminisced about being like a gypsy tribe who moved from place to place, often with the families living in trailers and helping each other with child care and various problems that came up.

Edited by Bill93
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Bill is correct, a lot of observations were done at night. Many were done in the day, and the term for the instrument used is a Heliotrope. Take a look at this book for a description of one: Heliotrope

If you read on you will see descriptions of other aspects of surveying in the field, including pre-Bilby tower towers, made of lumber and built at the site.


Here is a tower


Observation station (not on a tower)


Heliotropes (Plate 37)

Edited by mloser
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John F. Hayford during his service with U.S.-Mexican Boundary Commission in the 1890's resolved such a need for in field communications by utilizing Morse code. Once lights replaced heliotropes at the turn of the century, most observations were made at night and there were more reasons for the observers to have direct contact with the lightkeepers. For one, identification, also lights often had to be dimmed or brightened, messages relayed in emergencies and the like. In 1902 International Morse code was adopted as the vehicle to obtain that end.


Radios were tried early in the World War II period and caused enough problems to delay their general use for about 15 years, the major one being the conversations were picked up by nearby receivers. In one case, locals hearing the jargon, compounded by flashing lights thought foreign agents were in the area and reported the incidents to police, who went looking for spies and found instead, surveyors atop towers. And, as might be expected, there were a few complaints about profanity.


By about 1960 radio technology was improved and all units were so equipped. Another era ended. No longer would lightkeepers peer off into the darkness awaiting a light blinking Dash - Dot - Dot pause Dash - Dash - Dot or DG, translated, Done here, Go to next station.



Note Light on floor, the light went on platform about their head.




Edited by Z15
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PS - A major reason for using lights is that is was nearly impossible to see any other target at the distances employed. On our MDOT surveys we often used lights for longer distances where we could not get accurate sighting (heat waves etc). Actually the lights we had where smaller versions of those in the pic and were acquired from NGS back in the late 70's. MDOT supplied manpower to an NGS Tower and leveling project in SE Michigan in the late 70's (circa 1975) and when NGS was done they willed a lot equipment to the MDOT, lights, witness posts, shade umbrellas, misc survey gear.

Edited by Z15
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