SURVEYING INSTRUMENTS AND METHODS maps used in the every-day work of the oil man are constructed by various surveying methods. The information desired is obtained by the measurements of horizontal and vertical distances and angles. These may be obtained by one or a combination of several methods. The measurements of horizontal distances may be done either by pacing, graduated tape or chain or by stadia methods. For vertical measurements we have the aneroid barometer, engineer's spirit level and stadia methods.
Two of the above mentioned methods may be easily learned and put to practical use. They are pacing, for the measurement of horizontal distances and the use of the aneroid barometer for determining vertical distances or elevations.
Pacing Survey. The method of determining horizontal distances by means of the stride or pace is known as pacing. Distances so obtained are approximate, but quite often such results are of great value.
To determine the pace the following procedure is recom mended: measure out carefully a distance of several hundred feet on level ground, then starting at one end walk along this measured line towards the other end, using NATURAL steps, and counting them. From the figures so obtained the NATURAL step or stride may be calculated, for example: Distance measured =soo ft. = 6000 inches Number of steps taken = 200 6000= 2oo=3o, or thirty inches (21 feet), per stride.
When the measurement of any distance is required it simply necessitates walking over the distance, counting the number of steps taken and multiplied by the constant for each step, which will give the desired result.
Attention is called to a system in use by great many people, which necessitates the "stepping off" a certain distance, such as three feet for each stride. Any attempt to regulate the step to three feet will bring about poor results, as it requires unnatural walking. Sometimes it is also desirable that when a distance is paced that it should not lie observed by anyone present, so if natural steps are taken such a purpose will not be disclosed.
By using natural steps one may cover good distances with less effort and without the tiresome results of awkward walking, and obtain better results.
Experiments should be made with fast walking, pacing over rough and hilly ground as well as through tall grass. It will
take but a short time and one accustomed to pacing will obtain good results.
By the use of this method it is possible to determine the location of wells on a neighboring farm; one needs but to walk from the well at right angles to the nearest property line and the distance obtained will be correct to within a few feet. Pacing may be used for many practical purposes where exact figures are not needed.
Aneroid Barometer. The aneroid barometer is a handy and very useful instrument for the oil man, and by careful handling, elevations may be obtained and such knowledge used for prac tical purposes. (Fig. 19.) By use of it, it is possible to determine the elevation between wells, and calculate the amount of casing needed. It will also enable the calculation of the dip of the sand, and may be used to determine the elevation of surface outcrops. Unfortunately many speak unfavorably of the aneroid, but the instrument if carefully handled may be used with sufficient accuracy and speed, which may become very desirable in many instances.
The aneroid barometer is an instrument that shows the pressure of the atmosphere, and a good sensitive instrument will show the variation of pressure due to the difference in height of a few feet.
The weight of a column of air surrounding the earth may be likened to the weight of a number of books piled in order, and resting on one's hand; the greater the number of books, the higher the column and greater the pressure on the hand. Simi larly with air pressure, the column of air above a mountain will be less than the column of air over the adjoining valley. The aneroid is the instrument that measures this column of air, or atmospheric or barometric pressure. Such a pressure is most commonly measured with a mercurial barometer, but as it is not so easily carried around due to its size, the aneroid barometer is used which is compact and less fragile. The weight of the column of air acts upon an elastic top of an exhausted (vacuum) metallic box, and the pressure is magnified by means of a lever and shown by a dial or hand on a scale graduated to show elevations.