118 
SHIDY. 
Some gauges use profile paper; others use plain paper. Some 
run a day only, while others run a whole month without 
changing the paper. 
Probably the first automatic or self-registering tide gauge 
ever constructed was the one described by Henry R. Palmer, 
C. E., in the Phil. Trans, for 1831, pp. 209-213 ; it used pro¬ 
file paper, and each hour was marked by a hammer striking 
a steel arrow which revolved freely with a wind vane on the 
roof of the tide-house. A cross-bar on the shaft of the arrow 
indicated the exact position of the hour, while the arrow 
showed the direction of the wind at the time. Although 
from time to time many improvements have been made in 
automatic tide gauges, it is a little strange that the latest 
advance made in the gauges of the Coast and Geodetic Sur¬ 
vey, namely, that of the hour-marking attachment, is but 
little more than a return to what was done in the very first 
instrument of the kind of which we have any record. 
Maii}r forms of electrical tide gauges have been devised, 
in this country as well as in Europe. Such gauges require 
a higher grade of intelligence to maintain them in contin¬ 
uous action than is required to run mechanical gauges, and 
in consequence they have not met with favor in the United 
States. They have been used, however, in France, Germany, 
and even in Spain, although some of the tidal records from 
an electrical gauge at San Juan, Porto Rico, which have 
fallen into our hands, do not serve as a testimonial in favor 
of such methods of recording observations. The construe-' 
tion of automatic gauges has done much toward extending 
our knowledge of the tides, as they render it easier to obtain 
satisfactory observations. 
But the mere accumulation of observations does not ex¬ 
tend our knowledge very much. The great mass of records 
must be analyzed or discussed before useful results are ob¬ 
tained. All the early observations were confined, with rare 
exceptions, to the maxima and minima of the tides, and, al¬ 
though it was soon found that at many ports these were too 
irregular to make any practical use of, there was no other 
