t sufficiently reflect on the silent encroachments of
time, or remember, that no man is in more danger of doing little, than
he who flatters himself with abilities to do all. When I was forced out
of my retirement, I came loaded with the infirmities of age, to struggle
with the difficulties of a narrow fortune; cut off by the blindness of
my daughter from the only assistance which I ever had; deprived by time
of my patron and friends; a kind of stranger in a new world, where
curiosity is now diverted to other objects, and where, having no means
of ingratiating my labours, I stand the single votary of an obsolete
science, the scoff of puny pupils of puny philosophers.

In this state of dereliction and depression, I have bequeathed to
posterity the following table; which, if time shall verify my
conjectures, will show that the variation was once known; and that
mankind had once within their reach an easy method of discovering the
longitude.

I will not, however, engage to maintain, that all my numbers are
theoretically and minutely exact: I have not endeavoured at such degrees
of accuracy as only distract inquiry without benefiting practice. The
quantity of the variation has been settled partly by instruments, and
partly by computation: instruments must always partake of the
imperfection of the eyes and hands of those that make, and of those that
use them: and computation, till it has been rectified by experiment, is
always in danger of some omission in the premises, or some errour in the
deduction.

It must be observed, in the use of this table, that though I name
particular cities, for the sake of exciting attention, yet the tables
are adjusted only to longitude and latitude. Thus when I predict that,
at Prague, the variation will in the year 1800 be 24-1/4 W. I intend to
say, that it will be such, if Prague be, as I-have placed it, after the
best geographers in longitude, 14 30'. E. latitude 50 40'. but that this
is its true situation I cannot be certain. The latitude of many places
is unknown, and the longitude is known of very few; and even those who
are unacquainted with science will be convinced that it is not easily to
be found, when they are told how many degrees Dr. Halley, and the French
mathematicians, place the cape of Good Hope distant from each other.

Those who would pursue this inquiry with philosophical nicety, must,
likewise, procure better needles than those commonly in use. The needle,
which, afte