MANUAL OF TIDE OBSERVATIONS 25 



cal part is threaded inside to serve as a coupling between the float 

 well proper and a supporting section of pipe (fig. 14) . In the apex of 

 the cone there is a threaded 1-inch hole in which may be fitted a bush- 

 ing with a smooth bore intake opening of the size desired. Bushings 

 with openings I/2 inch, % inch, and % inch are provided with the 

 gage. 



60. Cleaning tool.— A special tool (15, fig.ll) is furnished with 

 the portable gage for use in cleaning the intake to the float well. 

 This consists of a cylindrical weight about li/^ inches in diameter 

 and 5 inches long containing in the bottom a pointed shank about 

 14 inch in diameter and 2 inches long. At the top is an eye for the 

 attachment of a line. 



PRIMARY TIDE STATION 



61. A primary tide station is one that is maintained over a period 

 of several years to obtain a continuous record of the tide in any 

 locality. As the records from such a station constitute basic tidal 

 data for present and future use, it is very important that the instal- 

 lation and maintenance of the station should be with the aim of 

 obtaining the highest degree of reliability and precision that is prac- 

 ticable. The essential equipment of a primary tide station includes 

 an automatic tide gage, float well, shelter, tide staff or equivalent 

 float- gage, and a system of bench marks. 



LOCATION 



62. Special care should be taken in the selection of a site for a 

 primary tide station. If possible, there should be a depth of not less 

 than 5 feet below the probable lowest tide. This is especially desir- 

 able in cold climates where kerosene is used in the float well to pre- 

 vent freezing, and also in exposed locations where storm waves of 

 large amplitude are common. When the determination of the height 

 of mean sea level is an important aim, the station should be located 

 on the open coast or in a bay with ample access of sea water. A 

 river or bay connected with the sea by a relatively small inlet is not a 

 suitable location for this purpose because of the probable difference 

 in the mean water level inside of the inlet and on the outer coast. 

 A place separated by a bar from the main body of water should in 

 general be avoided less the records obtained will not be representa- 

 tive of the tidal conditions in the general area. 



63. In selecting the site for a primary tide station it is very desir- 

 able that attention be given to the cleanliness of the surroundings. 

 Highly congested areas with a large amount of shipping should in 

 general be avoided. Because of the commercial need for space in 

 such areas, quarters obtainable for a tide station are usually cramped 

 and poorly lighted and ventilated. These conditions, together with 

 the presence of more or less refuse in the adjacent waters with accom- 

 panying offensive odors, tend to discourage the proper care of the 

 gage by the observer. Moreover, in such areas both the automatic 

 gage and tide staff are subject to dangers of disturbance from the 

 docking and loading of vessels. Especially, the tide staff may be 

 accidentally knocked out of place and resecured at a different eleva- 

 tion without any report of the incident. Heavy vehicular traffic 

 in such an area also renders the leveling between tide staff and bench 

 marks especially diflicult. 



