18 



U. S. COAST AND GEODETIC SURVEY 



attached to the ceiling of the tide house. The latter method is to be pre- 

 ferred as it increases the period during which tlie gage will operate 

 with a single winding up of the weight A weight of 1 pound is 

 recommended regardless of whether it is used with or without a mova- 

 ble pulley. When suspended from a movable pulley, the extra weight 

 of the latter offsets the reduced strain on the cord resulting from this 

 arrangement. 



39. Scale of gage. — The height scale of the gage depends upon the 

 circumference of the float pulley and the pitch of the pencil screw. 

 The different scale combinations are shown in the table below : 



Scale combinations 



In the above table the range limit of the curve shows the maximum 

 range that can be recorded by a continuous curve with the scale in- 

 dicated. Beyond this limit the pencil arm becomes disengaged from 

 the threads of the pencil screw and further rise and fall is registered 

 by a series of jogs near the margin of the paper. The extreme range 

 which can be recorded by these jogs depends upon the size of the 

 float drum. In the columns for the extreme range limit two values 

 are given for each scale. The first value is the limit when float and 

 counterpoise drums have a width of 1% inches, and the second value 

 when the width is 1% inches. 



PORTABLE AUTOMATIC TIDE GAGE 



40. The portable automatic tide gage was designed by this Bureau 

 primarily for use in obtaining short series of observations for the 

 reduction of soundings in hydrographic surveys. The aim was to 

 provide a gage more portable and more easily installed than the 

 standard gage. Besides being smaller, it differs in a number of ways 

 from the larger gage. It is equipped with a single roller and a single 

 clock movement, the latter being concealed inside the roller. A 

 counterpoise spring is substituted for counterpoise weight. It is 

 provided with a smaller float which operated in a convenient size 

 iron pipe which serves also as a support for the gage. An iron cover 

 protects the gage from the weather or molestation and eliminates the 

 necessity for any specially built shelter. The record is drawn on 

 sheets of cross-section paper which may be conveniently removed 

 from the gage when desired. Although some degree of the precision 

 of the standard gage has been sacrificed to gain the conveniences of 

 the smaller gage, it is sufficiently accurate for the purpose for which 



