56 



U. S. COAST AND GEODETIC SURVEY 



half-tide level or midway between the extreme tides to be expected 

 diirmg the period of observations. With such a setting the curve 

 traced by the portable gage will be approximately centered on the 

 record paper. 

 183. Float well.— The base of the portable automatic tide gage is 



provided with a 

 sleeve to fit on the 

 top of a float well. 

 In the later gages 

 this provides di- 

 rectly for a 4-inch 

 float pipe, but in the 

 earlier gages it pro- 

 vided only for a 

 314-inch pipe and a 

 reducing coupling 

 is necessary to 

 adapt it to the 

 larger pipe. The 

 pipe in addition to 

 serving as a float 

 well acts also as a 

 support for the in- 

 strument. When 

 the gage is installed 

 on a wharf a flange 

 coupling with a 

 short section of pipe 

 above the deck af- 

 fords a ready means 

 of supporting the 

 float pipe. The 

 conical inlet cou- 

 pling is screwed 

 on the bottom of 

 the longer section, 

 reaching below ex- 

 treme low water. 

 To provide a sup- 

 port for the instru- 

 ment in a location 

 at which no wharf 

 or platform is 

 available, an addi- 

 tional section of 

 pipe is screwed into 

 this conical inlet 

 couplmg on its bottom end and perforated with several large holes 

 to allow free access of the water to the inlet in the coupling. (These 

 holes should be as large as can be conveniently made, so as not to 

 become clogged.) This lower section rests on the bottom, and the 

 float pipe may be lashed to a single pile or net stake or lashed securely 

 against an overhanging cliff where depth of water permits (figs. 20 and 

 21). In localities where little penetration can be obtained for a single 



Figure 21. — Installation portable automatic tide gage against 

 rocky cliff. 



