It must also be borne in mind,
that by the latitude deduced by the mean of 1250 superior
culminations of Polaris by the same observers, the latitude of
Formentera was found to be 38deg a result
differing by 2from the mean of the 1318 inferior
culminations given above[This difference cannot be accounted
for by any difference in the tables of refraction, as neither
the employment of those of Bradley, of Piazzi, of the French, of
Groombridge, of Young, of Ivory, of Bessel, or of Carlini, would
make a difference of two-tenths of a second
These facts alone ought to have awakened the attention of Captain
Sabine, and of those who examined and officially pronounced on
the merits of his observations; for, supposing the skill of the
observers equal, it seems a necessary consequence that "the
performance of the six-inch circle is" not merely "fully equal to
that of circles of larger dimensions," but that it is decidedly
SUPERIOR to one of sixteen inches in diameter
This opinion did indeed gain ground for a time; but, fortunately
for astronomy, long after these observations were made,
published, and rewarded, Captain Kater, having borrowed the same
instrument, discovered that the divisions of its level, which
Captain Sabine had considered to be equal to one second each,
were, in fact, more nearly equal to eleven seconds, each one
being 10 This circumstance rendered necessary a
recalculation of all the observations made with that instrument:
a re-calculation which I am not aware Captain Sabine has ever
thought it necessary to publish [Above two hundred sets of
observations with this instrument are given in the work alluded
to It can never be esteemed satisfactory merely to state the
mean results of the corrections arising from this error: for the
confidence to be attached to that mean will depend on the nature
of the deviations from it
This is the more to be regretted, as it bears upon a point of
considerable importance to navigation; and if it should have
caused any alteration in his opinion as to the comparative merits
of great and small instruments, it might have been expected from
a gentleman, who was expressly directed by the Board of
Longitude, to try the question with an instrument constructed for
that especial purpose
Finding that this has not been done by the person best qualified
for the task, perhaps a few remarks from one who has no
pretensions to familiarity with the instrument, may tend towards
elucidating this interesting question
The following table gives the latitudes as corrected for the
error of level:
Station Star Latitude Latitude Diffe-
by Capt corrected for rence
Sabine error of level
deg
Sierra Leone Sirius 8 29 27
Ascension Alphenturi 7 55 46
Bahia Alphyrae 12 59 19
Alphyrae 21
Alphavonis 22
Maranham Alphyrae 2 31 42
Alphyrae 43
Alphavonis 44
Alphyrae 44
Alphygni 42
Alphruris 42
Trinidad Achernar 10 38 56
Alphruris 52
Achernar
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