Decline of Science in England by Charles Babbage (red white royal blue txt) đź“–
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those mentioned in the Act; and it recites the words of the Act,
that they shall be persons “WELL VERSED IN THE SCIENCES OF
MATHEMATICS ASTRONOMY, AND NAVIGATION.” Of the fitness of the
gentlemen who now hold those situations to pronounce judgment on
mathematical questions, the public will be better able to form an
opinion when they shall have communicated to the world any of
their own mathematical inquiries. Although it is the practice to
consider that acceptance of office is alone necessary to qualify
a man for a statesman, a similar doctrine has not yet prevailed
in the world of science. One of these gentlemen, who has
established his reputation as a chemist, stands in the same
predicament with respect to the other two sciences. It remains
then to consider Captain Sabine’s claims, which must rest on his
skill in “PRACTICAL ASTRONOMY AND NAVIGATION,”— a claim which
can only be allowed when the scientific world are set at rest
respecting the extraordinary nature of those observations
contained in his work on the Pendulum.
That volume, printed under the authority of the Board of
Longitude, excited at its appearance considerable attention. The
circumstance of the Government providing instruments and means of
transport for the purpose of these inquiries, placed at Captain
Sabine’s disposal means superior to those which amateurs can
generally afford, whilst the industry with which he availed
himself of these opportunities, enabled him to bring home
multitudes of observations from situations rarely visited with
such instruments, and for such purposes.
The remarkable agreement with each other, which was found to
exist amongst each class of observations, was as unexpected by
those most conversant with the respective processes, as it was
creditable to one who had devoted but a few years to the subject,
and who, in the course of those voyages, used some of the
instruments for the first time in his life.
This accordance amongst the results was such, that naval officers
of the greatest experience, confessed themselves unable to take
such lunars; whilst other observers, long versed in the use of
the transit instrument, avowed their inability to take such
transits. Those who were conversant with pendulums, were at a
loss how to make, even under more favourable circumstances,
similarly concordant observations. The same opinion prevailed on
the continent as well as in England. On whatever subject Captain
Sabine touched, the observations he published seemed by their
accuracy to leave former observers at a distance. The methods of
using the instruments scarcely differed in any important point
from those before adopted; and, but for a fortunate discovery,
which I shall presently relate, the world must have concluded
that Captain Sabine possessed some keenness of vision, or
acuteness of touch, which it would be hopeless for any to expect
to rival.
The Council of the Royal Society spared no pains to stamp the
accuracy of these observations with their testimony. They seem
to have thrust Captain Sabine’s name perpetually on their
minutes, and in a manner which must have been almost distressing:
they recommend him in a letter to the Admiralty, then in another
to the Ordnance; and several of the same persons, in their other
capacity, as members of the Board of Longitude, after voting him
a THOUSAND POUNDS for these observations, are said to have again
recommended him to the Master-General of the Ordnance. That an
officer, commencing his scientific career, should be misled by
such praises, was both natural and pardonable; but that the
Council of the Royal Society should adopt their opinion so
heedlessly, and maintain it so pertinaciously, was as cruel to
the observer as it was injurious to the interests of science.
It might have been imagined that such praises, together with the
Copley medal, presented to Captain Sabine by the Royal Society,
and the medal of Lalande, given to him by the Institute of
France, had arisen from such a complete investigation of his
observations, as should place them beyond the reach even of
criticism. But, alas! the Royal Society may write, and nobody
will attend; its medals have lost their lustre; and even the
Institute of France may find that theirs cannot confer
immortality. That learned body is in the habit of making most
interesting and profound reports on any memoirs communicated to
it; nothing escapes the penetration of their committees appointed
for such purposes. Surely, when they enter on the much more
important subject of the award of a medal, unusual pains must be
taken with the previous report, and it might, perhaps, be of some
advantage to science, and might furnish their admirers with
arguments in their defence, if they would publish that on which
the decree of their Lalande’s medal to Captain Sabine was
founded.
It is far from necessary to my present object, to state all that
has been written and said respecting these pendulum experiments:
I shall confine myself merely to two points; one, the transit
observations, I shall allude to, because I may perhaps show the
kind of feeling that exists respecting them, and possibly enable
Captain Sabine to explain them. The other point, the error in
the estimation of the division of the level, I shall discuss,
because it is an admitted fact.
Some opinion may be formed of transit observations, by taking the
difference of times of the passage of any star between the
several wires; supposing the distances of those wires equal, the
intervals of time occupied by the star in passing from one to the
other, ought to be precisely the same. As those times of passing
from one wire to another are usually given to seconds and tenths
of seconds, it rarely happens that the accordance is perfect.
The transit instrument used by Captain Sabine was thirty inches
in length, and the wires are stated to be equi-distant. Out of
about 370 transits, there are eighty-seven, or nearly one-fourth,
which have the intervals between all the wires agreeing to the
same, the tenth of a second. At Sierra Leone, nineteen out of
seventy-two have the same accordance; and of the moon
culminating stars, p. 409, twelve out of twenty-four are equally
exact. With larger instruments, and in great observatories, this
is not always the case.
Captain Kater has given, in the Philosophical Transactions, 1819,
p. 427, a series of transits, with a three and a half foot
transit, in which about one-eleventh part of them only have this
degree of accuracy; and it should be observed that not merely the
instrument, but the stars selected, have, in this instance, an
advantage over Captain Sabine’s.
The transit of M. Bessel is five feet in length, made by
Frauenhofer, and the magnifying power employed is 182; yet, out
of some observations of his in January, 1826, only one-eleventh
have this degree of accordance. In thirty-three of the Greenwich
observations of January, 1828, fifteen have this agreement, or
five-elevenths; but this is with a ten-feet transit. Now in none
of these instances do the times agree within a tenth of a second
between all the wires; but I have accounted those as agreeing in
all the wires in which there is not more than four-tenths of a
second between the greatest and least.
This superior accuracy of the small instrument requires some
explanation. One which has been suggested is, that Captain
Sabine employs a chronometer to observe transits with; and that
since it beats five times in two seconds, each beat will give
four-tenths of a second; and this being the smallest quantity
registered, the agreement becomes more probable than if tenths
were the smallest quantities noticed. In general, the larger the
lowest unity employed the greater will be the apparent agreement
amongst the differences. Thus, if, in the transit of stars near
the pole, the times of passing the wires were only registered to
the nearest minute, the intervals would almost certainly be
equal. There is another circumstance, about which there is some
difficulty. It is understood that the same instrument,—the
thirty-inch transit, was employed by Lieutenant Foster; and it
has not been stated that the wires were changed, although this
has most probably been the case. Now, in the transits which the
later observer has given, he has found it necessary to correct
for a considerable inequality between the first and second wires
(See Phil. Trans. 1827). If an erroneous impression has gone
abroad on this subject, it is doing a service to science to
insure its correction, by drawing attention to it.
Should these observations be confirmed by other observers, it
would seem to follow that the use of a chronometer renders a
transit more exact, and therefore that it ought to be used in
observatories.
Among the instruments employed by Captain Sabine, was a repeating
circle of six inches diameter, made by order of the Board of
Longitude, for the express purpose of ascertaining how far
repeating instruments might be diminished in size:—a most
important subject, on which the Board seem to have entertained a
very commendable degree of anxiety.
The following extract from the “Pendulum Experiments” is
important:
“The repeating circle was made by the direction, and at the
expense of the Board of Longitude, for the purpose of
exemplifying the principle of repetition when applied to a circle
of so small a diameter as six inches, carrying a telescope of
seven inches focal length, and one inch aperture; and of
practically ascertaining the degree of accuracy which might be
retained, whilst the portability of the instrument should be
increased, by a reduction in the size to half the amount which had
been previously regarded by the most eminent artists as the
extreme limit of diminution to which repeating circles, designed
for astronomical purposes, ought to be carried.
“The practical value of the six-inch repeating circle may be
estimated, by comparing the differences of the partial results
from the mean at each station, with the correspondence of any
similar collection of observations made with a circle, on the
original construction, and of large dimensions; such, for
instance, as the latitudes of the stations of the French are,
recorded in the Base du Systeme Metrique: when, if due allowance
be made for the extensive experience and great skill of the
distinguished persons who conducted the French observations, the
comparison will scarcely appear to the disadvantage of the
smaller circle, even if extended generally through all the
stations of the present volume; but if it be particularly
directed to Maranham and Spitzbergen,—at which stations the
partial results were more numerous than elsewhere, and obtained
with especial regard to every circumstance by which their
accuracy might be affected, the performance of the six-inch
circle will appear fully equal to that of circles of the larger
dimension. The comparison with the two stations, at which a more
than usual attention was bestowed, is the more appropriate,
because it was essential to the purposes for which the latitudes
of the French stations were required, that the observations
should always be conducted with the utmost possible regard to
accuracy.
“It would appear, therefore, that in a repeating circle of six
inches, the disadvantages of a smaller image enabling a less
precise contact or bisection, and of an arch of less radius
admitting of a less minute subdivision, may be compensated by the
principle of repetition.”
Captain Sabine has pointed out Maranham and Spitzbergen as places
most favourable to the comparison. Let us take the former of
these places, and compare the observations made there with the
small repeating instrument of six inches diameter, with those
made by the French astronomers at Formentera, with a repeating
circle of forty-one centi-metres, or about sixteen inches in
diameter, made by Fortin. It is singular that this instrument
was directed, by the French Board of Longitude, to be made
expressly for this survey, and the French astronomers paid
particular attention to it, from the circumstance of
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