Page 157 control and signal building 2723 



To construct a tripod signal, three pieces of 2- by 4-inch by 16-foot lumber are selected for the 

 legs and one 3- by 3-inch by 16-foot piece for the centerpole. The upper ends of two of the legs are 

 sawed at an angle of approximately 35° so that they will fit snugly when the tripod is raised in place. 

 Holes to take a %-inch bolt are bored near the upper ends of the three legs and about 8 feet from the 

 lower end of the centerpole. The holes are bored through the 2-inch width of the legs, perpendicular 

 to the sides of the unsawed leg but at an angle through the other two, so that they are approximately 

 perpendicular to the sawed faces. 



The target is next nailed on the centerpole. It may be either signal cloth tacked to wooden cross- 

 pieces, or eight Yi- by 6-inch by 3-foot slats. The portion of the centerpole between the target and 

 the bolt hole is wrapped with white and black signal cloth. Four guy wires are then fastened to the 

 top of the centerpole leading out through the crossed target. The legs and centerpole are then bolted 

 together and placed flat on the ground with one leg pointing directly offshore. 



If the station is to be occupied, the lower part of the centerpole will have to be sawed off about 

 6% feet above the ground so the theodolite can be set up over the station mark and to provide head 

 room for the observer without having to dismantle the tripod. If a 5-foot length is spliced to the 

 bottom of the centerpole and a headless nail driven part way into the center of the lower end of the 

 extension, the centering of the target can be quickly and easily performed, when the tripod is raised 

 into place, by inserting the nail into the drilled hole in the center of the station-mark disk. This serves 

 as a pivot while the centerpole is being plumbed, and when it is vertical, it is naturally centered at 

 the same time. The plumbing may be accomplished by suspending a plumb bob at arm's length and 

 alining the centerpole by eye along the plumb-bob string. 



After the target has been centered over the station, the guy wires are secured, the centerpole 

 is secured by cross braces to the legs of the tripod, and the tripod legs nailed to stakes driven in the 

 ground. The seaward sides of the signal are then dressed with rough boards, spaced about the width 

 of the boards apart, and whitewashed, if desired, or spaced about 2 feet apart with signal cloth securely 

 tacked on to cover the space between. When signal cloth is used, it should be slashed with a knife to 

 diminish wind pressure and to render the cloth useless for other purposes so that it will be less likely 

 to be stolen. An opening should be left at the height of the telescope to permit observations to be 

 made without having to tear loose any of the signal cloth (see fig. 43), but such an opening is unneces- 

 sary if boards are used, as one or two boards can be easily removed and restored to place after the 

 observations have been made. After the construction and dressing of the tripod have been completed, 

 the lower part of the centerpole should be sawed off at the desired height and the centering of the 

 pole and target checked. 



If the station is not to be occupied, a slightly different construction will be more convenient. The 

 bolt hole should be bored in the centerpole 10 feet from the bottom, insteac^of 8 feet A headless nail 

 is driven part way into the center of the bottom of the centerpole — a splice is unnecessary. The 

 tripod legs should be about 13 feet long as the apex of the tripod need not be as high as is required for 

 a station to be occupied. The tripod is then constructed and dressed as described above, except that 

 no opening for instrument observations is necessary and the centerpole need not be sawed off. The 

 bottom of the centerpole should be braced by 1- by 2-inch stakes. 



Regardless of whether a tripod is constructed so as to be occupied or not, the guying and size of 

 the lumber used for dressing depend mainly on the strength of wind prevalent in the particular lo- 

 cality. If strong winds are infrequent, the guy wires may be omitted entirely, especially if the tripod 

 is exposed to livestock. For dressing, 1- by 6-inch boards are best as any smaller size is too light to 

 support a man's weight on the longer lower sections. A nice dressing is made of 1- by 12-inch boards 

 but the cost is high in comparison with 1- by 6-inch boards. Rough lumber is best for dressing as it 

 is less expensive and will take whitewash better than surfaced lumber. Scrap lumber found on the 

 beach can sometimes be used but its presence should not be relied on. 



If strong winds prevail, the target should be constructed of eight J-^- by 6-inch by 3-foot slats 

 spiraled around the top of the centerpole, and eight guy wires should be used instead of four, with the 

 second set leading from the apex of the tripod. Signal cloth should be used for dressing instead of 

 boards, so that in case of gales the signal cloth will be torn away rather than the entire tripod 

 demolished. The signal cloth can be replaced easier than a new tripod can be built. The lower 

 half of the signal cloth on a tripod should be tacked to pieces of 2- by 4-inch lumber rather than 1- 

 by 6-inch boards. Even these have been broken in the center by violent storms frequently encoun- 

 tered in some areas. 



