28 U. S. COAST AND GEODETIC SURVEY 



from 5 to 6 feet below the lowest probable tide. It is desirable, how- 

 ever, that there be sufficient depth below the intake to make it un- 

 likely that it will become covered by a shoaling of the water in the 

 vicinity. It is desirable that the top of the well extend several inches 

 above the floor of the tide house for convenience of access and also to 

 lessen the chance of objects on the floor accidentally falling into the 

 well. For an iron float well, a flanged collar at the top may be ar- 

 ranged to rest upon iron plates secured to the floor of the wharf. The 

 well should be strongly braced in position. 



71. Precaution against freezing. — In cold climates kerosene is 

 generally used in float wells to prevent freezing. The column of 

 kerosene should be from 2 to 5 feet in height, depending upon the 

 severity of the winters. A 12-inch cylindrical pipe will require about 

 6 gallons of kerosene for each foot of height and a 12-inch square 

 float well about 7y2 gallons for each foot of height. The amount of 

 kerosene which can be retained in the float well will be limited by the 

 depth of the intake below the lowest tide. When an iron float well 

 is used and the intake is sufficiently low, the kerosene introduced at 

 the time of installation may remain for many years, the loss from 

 evaporation being small. In a wooden float well there is more or less 

 leakage and the supply of kerosene must . be renewed at frequent 

 intervals. 



72. As the specific gravity of kerosene is less than that of water, 

 the surface of the kerosene in the float well will stand above the 

 water level outside, the difference in level being approximately equal 

 to one-eighth the entire height of the column of kerosene. Note 

 should therefore be entered in the record whenever kerosene is intro- 

 duced into the well and a comparative staff reading taken before and 

 after this is done. In the tabulation of the automatic tide gage 

 record, the effect of this height difference is eliminated in the com- 

 putations involving the comparative staff readings. It is very im- 

 portant, however, that no kerosene shall he used in a -float well 

 designed for a tape gage or other nonregistenng float gage the read- 

 ings from which are to he taken directly, as errors of indeterminate 

 amounts may thus he introduced. 



TIDE HOUSE 



73. When sufficient space is available, the tide house should be ap- 

 proximately 6 feet square and from 7 to 8 feet high. A house of this 

 size provides room for the tide observer to move around the gage and 

 give it such attention as may be required. The house should be well 

 lighted by windows, neat in appearance, and painted to conform 

 with other buildings in the immediate vicinity. A standard sign 

 with the following inscription will be provided upon requisition : 



U. S. DEPARTMENT OF COMMERCE 



COAST AND GEODETIC SURVEY 



TTOE STATION 



, 74. The tide house will in general be placed over the top of the float 

 well so that the wire from the gage may be led directly to the auto- 

 matic tide gage. When this arrangement is impracticable, the float 

 wire may be led from the float well over a system of pulleys and 

 through a suitable conduit to the gage in the tide house. When this 



