ON EFFECT OF WIND AND ATMOSPHERIC PRESSURE ON THE TIDES. 507 
of Glasson Dock. The results deduced were based on observations 
made over a lengthened period of the atmospheric gradients in the Irish 
Sea from the south of St. George’s Channel to Morecambe Bay. The 
mean gradient over this distance—over 240 miles—he found to be 
0-043 in., the mercury standing higher to that amount in the south. 
He also states that no storm of serious extent prevails over the United 
Kingdom, unless there be a difference of pressure between any two 
stations of the Meteorological Department exceeding } in., and that the 
force of wind on the Beaufort scale does not exceed from five to six, 
unless the gradient is as high as 0-02 in fifteen miles. On the data 
obtained, Captain Greenwood prepared a table for use on that part of the 
coast, showing the effect of the difference of the gradient on the tides. 
This table is given in the ‘Kludometric’ Tide Table published by him 
annually. 
From an analysis of the tides at five ports round the coast, given in 
the following tables, it will be seen that, taking all tides raised or lowered 
more than six inches from the calculated height, when the wind was 
blowing with a force less than three of the Beaufort scale, coincident with 
a variation in atmospheric pressure of 0°25 inch from the average, 
the number of tides affected by the pressure, as recorded by the barometer 
reading at local stations in a manner that would naturally be expected, 
was nearly equal to those affected in a contrary direction, 56 per cent. 
being depressed when the pressure was above the average, or raised when 
it was below, and 44 per cent. being influenced in the opposite direction. 
These results indicate that the reading of the barometer at a single 
port is not a reliable guide as to the effect of pressure in raising or 
lowering the height of the tide, and that no reliable data as to the effect 
of atmospheric pressure on the tides can be arrived at, except by simul- 
taneous observations of the barometer, the wind, and the tides over 
extended areas of both land and sea. 
BAROMETER AND THE TIDES. 
Boston—Average of the Four Years 1892, 1893, 1894, 1895. 
Average M ._ |Mean varia-| Maxi- |Mean varia- 
number of Tide” tion of mum tion of 
— Tides ° , Bale Tide from | varia- | Barometer 
affected in LWst predicted | tionof | from 
one year oY paces aad height Tides average 
1891. Ft. In. In. Tn. 
| High Bar.—Low Tides . | 48 18°51 10°72 bys) 367 
mone? |,,)) Eigh’ .,, 17 19°54 9:90 20 439 
Total and Means 65 19:02 9°81 — | 403 
High Bar.—High Tides . 32 20°60 9°69 29 B76 
Low , Low ,, 13 18°14 10°59 27 “B99 
¥ | rs 
Total and Means A 45 19°37 10:13 — “B87 
1892. 
High Bar.—Low Tides 45 18°60 9:62 — 371 
Low , High ,, 15 19-00 8°66 = 466 
Total and Means 60 18:80 9:14 —_ “418 
a 8 EE 
