STATE OF PROGRESS OF OUR KNOWLEDGE OF 
THE TIDES. 
BY 
L. P. Shidy. 
[Read before the Society March 17, 1900.] 
As the first step toward a knowledge of any inductive 
science is the collection of observations, it may be well to 
allude briefly to the advances made in our means of secur¬ 
ing tidal records. Passing by the numerous forms of gauges 
which require the presence of an attendant to take down 
their indications at stated times, such as the ordinary fixed 
tide staff, box gauges of many kinds, spar gauges, tripod or 
pulley gauges, and non-recording siphon gauges, each of 
which has its uses, and may be well adapted to the condi¬ 
tions under which the observations are made at various 
stations, let us consider the automatic or self-registering tide 
gauges for a few moments. 
The object of these gauges is to make a record, usually in 
the form of a curve, which will enable one to readily find 
the height of the sea at any time within the limits of the 
record. The essential parts of any form of automatic tide 
gauge are as follows: a , some kind of clock or time-piece; b, a 
float, loosely confined within a vertical box or tube, the lower 
end of which is partially closed; and c, some mechanism for 
recording time and height, either continuously or at short 
discrete intervals of time. While in some instances an un¬ 
reasonable effort is made to secure a record on the natural 
scale, even using paper six or more feet in width when nec¬ 
essary, other forms of gauges go to the opposite extreme and 
reduce the record down to less than two inches in width. 
17—Bull. Phil. Soc., Wash., Vol. 14. 
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