OF CORNWALL. 53 
deep as where the rivers and creeks run farther up into the land : 
they are therefore more apt to be choaked with lands and rubbilh 
than in other fituations. Too much care therefore cannot be taken 
that Tips difcharge not their ballaft in improper places, fo as to ob- 
ftrud the navigable channel, a grievance of which many intelligent 
traders are apprehenfive, as it may affe& our Sea-coafts in time, 
when a remedy may not eafily be found out. The higheft tide, 
in equal circumftances, is about two days and a half clear after the 
new and full moon. The tide is later than at London Bridge one 
hour and fifty-five minutes. The variation of the needle at the 
Land’s End has for fome years been reckoned above eighteen degrees 
Wefterly ; but in the month of October, 1757, at Carelew Houfe, 
on one of the branches of Falmouth Harbour, it was, by a needle of 
ten inches and half long, found to be nineteen degrees twelve mi- 
nutes Wefterly. Dr. Halley x , in the year 1700, found it to be no 
more than feven degrees and a half Wefterly ; but whether the 
increafe has been regular and gradual, for want of a continued feries 
of obfervations, I cannot determine. 
Such is the common ordinary ftate of our Sea in Cornwall, as 
to tides, creeks, harbours, and charts ; but indeed the tides are 
greatly accelerated or retarded, not only by the projection of fo 
many head-lands, the depths of bays and creeks, and the indraught 
of the North and South Channels, but by different winds, and yet 
the moft extraordinary phcenomenon which has ever appeared on 
thefe coafts, as far as I can learn, proceeded from neither of thefe 
caufes. On the ift of November, 1755, about two o’clock in the 
afternoon, the Barometer being at the higheft I have noted it for three 
years paft, Farenheit’s Mercurial Thermometer at 54, the fane point- 
ing to the North-Eaft in a flat calm, the Sea, about half an hour 
after ebb, was obferved, at the pier of St. Michael’s Mount, to rile 
fuddenly, and then to retire. This attracted the attention of the 
fpectators, and to their great amazement, ten minutes after, the 
Sea rofe near fix feet, coming in from the South-Eaft extremely 
rapid ; it then ebbed away with the fame rapidity to the Weftward 
for about ten minutes, till it was near ,fix feet lower than before ; 
it then returned again, and fell again in the fame fpace of time, and 
continued the agitation, alternately rifing and falling, each retreat 
and advance nearly of the fpace of ten minutes, till five hours and 
a half after it began. During this agitation the Seyn-boats, riding 
at the head of the pier, were whirled fome one way, fome an- 
other ; and the filhermen endeavouring to bring fome boats into the 
pier, they were hurried in and out of the mouth of the pier, as the 
* Letter to the author frorn Mr. Charles Heydon, Math, inftrument-maker, October 3, 1754. 
P Sea 
