Coast Survey of the United States.  . 241 
the observations will be calculated for the effect of winds, and 
barometric pressure, and the variations in the times and heights of 
high water due to changes in the moon’s parallax, declination, and 
motion in right ascension, will be investigated by a comparison 
between computation and observation. 
The practical benefits of this system in determining the tide- 
factors, and in tracing the times, courses, and conflicts of the tides 
in the harbors and inland seas of the United States, cannot be 
too strongly enforced. And perhaps even the further suggestion 
may be humbly ventured, notwithstanding the unpromising re- 
sults of Prof. Whewell’s endeavors, that predictions to be relied 
on, which would be infinitely serviceable in the preservation 
of life and property in some of our bays and rivers, can be based. 
upon future accumulated observations. If this hope should ul- 
timately prove fruitless, no one will deny that so noble an object 
is worthy an effort. 
Dr. Bache has also begun to set up self-registering tide- 
gauges—one has been in operation during the last six months, at 
Governor’s Island, another is now in process of construction at 
the office in Washington. ‘The former of these was invented, 
in its details, by Mr. Wightman, philosophical instrument-maker 
in Boston. The axis of a hollow copper cylinder, upon which 
the paper is secured, is connected with the pinion of a clock, 
and revolves correspondingly to the hands. The rim of a cyl- 
inder is divided in parts of an hour, and these divisions are trans- 
ferred to the paper by a rule ingeniously contrived. A brass 
chain, (guided by the requisite pullies,) with the float in a well 
at one end, and a weight at the other, passes round a wheel in 
the prolonged axis of which, directly over the cylinder, is fixed 
the pencil. The well is guarded from the external motion of 
the water, and the motion of the float is communicated to the 
pencil by means of a screw. 
The second tide-gauge is the invention of Mr. Saxton, late the 
balance maker of the U.S. Mint, and there particularly distinguish- 
ed for his improvement of the parallel ruling-machine, by which it 
was made perfectly useful, after being thrown aside in despair by 
the original inventor. Mr. Saxton is now the constructor at the 
office of weights and measures, at Washington. His tide-gauge 
has two cylinders. One is carried by the clock, and receives the 
paper after the tidal curve is traced. ‘The other carries the blank 
