CHAPTER II, SECTION 1A perienced during much of the survey. Station Coca in the lagoon consisted of four steel pilings driven in the top of a coral pinnacle, cross-braced, and decked with a wooden platform and instrument stand. As the pinnacle was approximately 24 feet below the surface of the lagoon, it was necessary to observe at low tide to minimize vibration. Figure 2-6 shows this station completed. The first two attempts to drive piles failed, the trouble experienced during construction being due primarily to heavy seas and high wind velocities. The third attempt was successful. A prefabricated platform was erected and the station was completed in April 1953. All observing was accomplished at night using lights for targets. A Wild T-2 theodolite was used for observing and proved very satisfactory. Station lights were constructed using the reflectors and lenses from U.S. Navy battle lamps. The lights were equipped with rheostats which permitted dimming the lights to the correct intensity for a sharp target. Continuous interstation communication was considered necessary due to the remote location of the stations. Figure 2-5. Survey Tower, Site How the scheme, and the relation to the schemeof six additional USN stations was determined. Figure 2-5 shows one of these earlier stations on site How. Other stations were established to second and third order specifications at various locations by local triangulation and traverse. The distribution of the stations of the completed network was such that destroyed stations can generally be replaced with a minimum of field work by observing a single triangle using the known line between two existing stations as a base. Where practical, to simplify reference to the stations, they were given the island code name of the location. FIELD PROCEDURE.A tentative layout of the scheme determining the locations where stations would be required was made from a study of the Atoll chart. The location of the base line, including a lagoon station to obtain a strong base expansion figure, resulted from this study. A field reconnaissance of these locations was made and station markers established. The stations were located inland from high tide line, sacrificing some convenience to reduce the possibility of damage or destruction from wave action. The height of the observing towers was determined so as to provide a minimum often feet vertical clearance over any obstruction or over the surface of the lagoon, in a long over-water sight line. Bilby steel towers were erected at locations requiring a tower height of over 20 feet. Lower towers were constructed of wood. The towers were adequately braced and guyed but some difficulty from wind vibration was exPage 2-22 Figure 2-6. Coco Head Triangulation Station