Leeds, Jan. 28. 1851.
The Ring Dial, perhaps the most elegant in principle of all the forms of
sun dial, has not, I think, fallen into greater disuse than have sun dials
of other constructions. To describe, in this place, a modern ring dial, and
the method of using it, would be useless: because it is an instrument which
may be so readily inspected in the shops of most of the London opticians.
Messrs. Troughton and Simms, of Fleet Street, make ring dials to a pattern
of about six inches in diameter, costing, in a case, 2_l_. 5_s_. They are,
in truth, elegant and instructive astronomical toys, to say the least of
them; and indicate the solar time to the accuracy of about two minutes,
when the sun is pretty high.
Formerly, ring dials were made of a larger diameter, with much costly
graduation bestowed upon them; too heavy to be portable, and too expensive
for the occasion. For example, at the apartments of the Royal Astronomical
Society, at Somerset House, a ring dial, eighteen inches in diameter, may
be seen, constructed by Abraham Sharp, contemporary and correspondent of
Newton and Flamstead; one similar to which, hazarding a guess, I should
say, could not be made under 100_l_. At the same place also may be seen,
belonging to Mr. Williams, the assistant-secretary of the society, a very
handsome oriental astrolabe, about four inches in diameter, richly chased
with Arabic characters and symbols; to which instrument, as well as to
modern ring dials, the ring dials described in "NOTES AND QUERIES" (Vol.
iii., p. 52.) seem to bear relation. If I recollect right, in one of the
tales of the _Arabian Nights_, the barber goes out, leaving his customer
half shaved, {108} to take an observation with his astrolabe, to ascertain
if he were operating in a lucky _hour_. By his astrolabe, therefore, the
barber could find the _time_ of day; _this_, however, I confess I could not
pretend to find with the astrolabe in question. Ring dials, as I am
informed, are in demand to go out to India, where they are in use among
surveyors and military men; and, no doubt, such instruments as the
astrolabe above-mentioned, which, though pretty old, does not pretend to be
an antique, are in use among the educated of the natives all over the East.