504 REPORT—1896. 
This article has been translated into English. It contains valuable 
information and statistics bearing on this subject. 
The analysis of the Tidal Records of the ports of Liverpool, Ports- 
mouth, Sheerness, Boston, and Hull has occupied all the time available. 
Had more opportunity been afforded it was intended to extend the investi- 
gation over a greater number of years. 
In considering the report it must be borne in mind that the object of 
the investigation was only for the practical purpose of ascertaining 
whether the records of the wind and atmospheric pressure as obtained by 
an observer at any particular port afforded a reliable guide to pilots and 
mariners navigating vessels over bars and up the channels of tidal rivers, 
and to those engaged in coast work, as to the variations to be expected in 
the height of the tides from those ascertained by calculation and given in 
the Admiralty or local tables. 
The deductions to be drawn from a careful examination of the 
information embodied in the following tables are— 
1. That the tides are influenced both by atmospheric pressure and by 
the wind to an extent which considerably affects their height. 
2. That the height of about one-fourth of the tides is affected by wind. 
3. That the atmospheric pressure affecting the tides operates over so 
wide an area that the local indications given by the barometer at any 
particular port do not afford any reliable guide as to the effect on the tide 
at that port. 
4. Thatalthough, so far as average results go, there can be traced a direct 
connection between the force and direction of the wind, and the variation 
in the height of the tides, yet that there is so much discrepancy in the 
average results when applied to individual tides that no reliable formula 
can be established for indicating the amount of variation in the height of 
the tide due to any given force of wind. 
5. The results given in the tables relating to atmospheric pressure 
indicate that the effect of this is greater than has generally been allowed, 
a variation of half an inch from the average pressure causing a variation 
of 15 inches in the height of the tides. 
It has sometimes been stated that an abnormally high tide is fol- 
lowed by a correspondingly low ebb. The investigations of the Dutch 
Engineers on the coast of Holland indicate that the effect of gales on the 
tides is to raise both the low and high water level. 
The accompanying diagrams of the tides of December 1895 at 
Flushing, sent by M. Ortt, and of the corresponding tides on the Clyde, 
sent by Mr. James Deas, show that on this occasion the result of the gale 
was to raise the mean level of the sea at those places during the gale. 
Atmospheric Pressure and the Tides. 
The variation in the pressure of the atmosphere on the surface of the 
sea must exercise a considerable effect on the tides. It is, however, very 
doubtful whether any reliable forecast of the effect can be deduced from 
the readings of the barometer at any one station. Water being practically 
incompressible, the variation of pressure on the whole surface of a basin 
filled with water, to which there is no outlet, cannot have any effect in 
raising or lowering the surface. If, however, the pressure is high over 
one part of the basin and low on the other part, a variation in the height 
of the water in one part, as compared with the other, will take place. 
