MAJSFUAL OF TIDE OBSERVATIONS 29 



is necessary, facilities should be provided for the convenient replace- 

 ment of a broken float wire by the tide observer. The top of the 

 float well must be provided with a suitable cover as a precaution 

 against the accidental dropping of anything into it. 



75. A table or shelf must be provided for the support of the tide 

 gage. A shelf can be conveniently constructed by setting the ship- 

 ping box of the tide gage on one end and then laying boards from 

 this to a cleat nailed to the wall of the tide house. The box and 

 boards are secured by screws which may be easily removed when it 

 is necessary to dismantle the gage. By hinging the cover of the 

 shipping box a convenient cupboard is formed for the storage of extra 

 tide rolls and other small articles. 



INSTALLATION OF TIDE STAFF 



76. Each primary tide station must be equipped with a tide staff 

 or equivalent tape gage to provide a temporary datum and reference 

 scale for the automatic gage record. The tide staff, which is de- 

 scribed on page 2, is to be used in .preference to a tape gage when 

 practicable. In selecting the location for the tide staff consideration 

 should be given to convenience in taking accurate readings and also 

 in leveling between staff and bench marks. The staff must be reason- 

 ably near the automatic gage to avoid any long delay between the 

 reading of the staff and the recording of the reading on the auto- 

 matic gage record, and should be placed so that the graduations are 

 clearly visible to the tide observer from an easily accessible position. 



77. Special attention should be given to placing the tide staff ,so 

 that its elevation may be conveniently checked by levels to bench 

 marks. There should be sufficient clearance above the staff to hold 

 the leveling rod in a vertical position. Sometimes a fixed tide staff 

 can be so located that it can be sighted upon directly from a leveling 

 instrument set up on the shore ; but when this is possible only during 

 low water, other arrangements should be made in order that a level- 

 ing party may not be unduly delayed by an unfavorable stage of the 

 tide. 



78. When installing a tide staff care must be taken to secure it in 

 a vertical position. The piling of a wharf often offers a convenient 

 support for a tide staff, but if an inclined pile is used for the purpose 

 offsets must be provided to keep the staff vertical. At the time of the 

 original installation, the exact elevation of the staff zero is usually 

 unimportant and it is the general aim to place the zero sufficiently 

 low to avoid frequent negative readings. However, if it is desired to 

 set the zero at some previously determined datum, such as mean low 

 water, the staff graduations must extend negatively below the zero. 

 After installation it is very important that the zero be maintained at 

 a fixed elevation, and any known or suspected change should be 

 reported to the office. 



INSTALLATION OF TAPE GAGE 



79. In exposed localities where rough water renders the use of a 

 tide staff impracticable, a nonregistering float gage may be substi- 

 tuted for the staff. The most satisfactory gage of this type now 

 in use by this office is a tape gage (fig. 2) with a graduated steel 



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