r long experience, I recommend to mariners, must be of pure
steel, the spines and the cap of one piece, the whole length three
inches, each spine containing four grains and a half of steel, and the
cap thirteen grains and a half.

The common needles are so ill formed, or so unskilfully suspended, that
they are affected by many causes besides magnetism; and, among other
inconveniencies, have given occasion to the idle dream of a horary
variation.

I doubt not but particular places may produce exceptions to my system.
There may be, in many parts of the earth, bodies which obstruct or
intercept the general influence of magnetism; but those interruptions do
not infringe the theory. It is allowed, that water will run down a
declivity, though sometimes a strong wind may force it upwards. It is
granted, that the sun gives light at noon, though, in certain
conjunctions, it may suffer an eclipse.

Those causes, whatever they are, that interrupt the course of the
magnetical powers, are least likely to be found in the great ocean, when
the earth, with all its minerals, is secluded from the compass by the
vast body of uniform water. So that this method of finding the
longitude, with a happy contrariety to all others, is most easy and
practicable at sea.

This method, therefore, I recommend to the study and prosecution of the
sailor and philosopher; and the appendant specimen I exhibit to the
candid examination of the maritime nations, as a specimen of a general
table, showing the variation at all times and places for the whole
revolution of the magnetick poles, which I have long ago begun, and,
with just encouragement, should have long ago completed.

[1] An account of an attempt to ascertain the longitude at sea, by an
exact theory of the variation of the magnetical needle; with a table of
variations at the most remarkable cities in Europe, from the year 1660
to 1860. By Zachariah Williams.

CONSIDERATIONS ON THE
PLANS OFFERED FOR THE CONSTRUCTION
OF BLACKFRIARS BRIDGE.

In three letters, to the printer of the Gazetteer.

LETTER I.

SIR, Dec. 1, 1759.

The plans which have been offered by different architects, of different
reputation and abilities, for the construction of the bridge intended to
be built at Blackfriars, are, by the rejection of the greater part, now
reduced to a small number; in which small number, three are supposed to
be much superiour to the rest; so th