1st NYVER HOME
History Past Present
Historical Pictures Reenactment Pictures
Project Pictures
Surveying Lesson 1
Surveying Lesson 2
Surveying Lesson 3
Walker Pension
Period Surveying Techniques
Methods of measuring distance with period techniques.
By Lt. Vernon Catron 1st New York Volunteer Engineers, Company A
Several months ago I was asked to write a brief article on different aspects of surveying with period techniques by Major Poe. This is the first article in the series.
Measuring is a major principal of surveying and construction. The methods that I will discuss are physical measuring and the use of stadia. Both of these require practice to become proficient.
I will first method is direct measurement. This can be done in several ways, pacing, and chaining.
Beginning with pacing. Pacing is done by counting your strides and multiplying by the average length of your stride. This average is calculated by measuring the distance covered by 100 paces at several different times. This method is used to keep track of your distance traveled on foot. If you have ever done orienteering you have used this method. This is used to obtain rough distances and measures surface distance.
Chaining or taping is the procedure by which you measure using chains or a tape. A standard "Surveyor’s Chains" is 66 feet in length, which equals 4 rods(16.1/ft/rod) or 100 links (6.6 inches/link). There are chains in 10 meter lengths (100 links). Tapes are made in steel or woven fiberglass and come in all lengths.
The correct technique for measuring horizontal distance requires the use of plumb bobs. The chain is pulled tight from your starting point and is held as level as possible. At the point that you want to measure you drop the plumb to the point and read the measurement. This requires a lot of practice to be good. If you are using a tape you should "Cut a Foot" while measuring. That is measure from a point 1 foot from the zero end of the tape to insure better accuracy. When you "Cut a Foot" remember to take that into account when working with the measurements. Be sure to pull the tape or chain the same way every time. If you are measuring a distance greater than your tape or chain you need to use chaining pins and transit to assure accuracy. This is done by locking the transit in the horizontal plane and moving the scope up or down as necessary to keep the tape/chain on line with your beginning point. When you are at the end of the chain and are on line set a chaining pin and continue as before staying on line. Please be aware that there are adjustments to the measurements to take into account temperature and humidity. These adjustments are found in any good surveying handbook, and will come with a surveyors tape.
Today there are electronic instruments that can measure using laser, infrared, and sound. Chaining or taping is the most accurate method we have to use for period measuring.
The stadia method is good when accuracy of 1/400 is acceptable. In a transit there are 3 horizontal wires and 1 vertical wire. The center horizontal wire is used for normal sights. The top and bottom wires are the stadia lines. The principal is relatively simple when you take a reading at 100’ the distance between the top and bottom wires is 1’. Therefore Distance = 100 * S (stadia). The transit or level must be horizontal for this formula to work. See Figure 1.
Figure 1
There is a way to calculate inclined stadia using the following formulas: Please refer to Figure 2.
|
|
|
|
|
|
Figure 2
As you can see the method for the transit locked in horizontal is much easier.
How can we apply this to living history? While working with artillery the stadia method can be used to set ranges. While mapping stadia can be used to measure distances.