Whether the first of these causes has ever operated can be best explained by those gentlemen who have been on the Council. The refusals are, notwithstanding the President"s taciturnity on the subject, better known than he is willing that they should be.
Having discussed the general policy of the measure, with reference both to the Society and to the public, and without the slightest reference to the individuals who may have refused or accepted those situations, I shall now examine the propriety of the appointments that have been made.
Doubtless the gentlemen who now hold those situations either have never considered the influence such a mode of selection would have on the character of the Council; or, having considered it, they must have arrived at a different conclusion from mine. There may, however, be arguments which I have overlooked, and a discussion of them must ultimately lead to truth: but I confess that it appears to me the objections which have been stated rest on principles of human nature, too deeply seated to be easily removed.
That I am not singular in the view I have taken of this subject, appears from several circ.u.mstances. A question was asked respecting these appointments at the Anniversary before the last; and, from the nature of the answer, many of the members of the Society have been led to believe the objections have been removed. Several Fellows of the Society, who knew these facts, thought it inexpedient ever to vote for placing any gentleman on the Council who had accepted these situations; and, having myself the same view of the case, I applied to the Council to be informed of the names of the present Scientific Advisers. But although they remonstrated against the PRINCIPLE, they replied that they had "NO COGNIZANCE" of the fact.
The two first members of the Council, Mr. Herschel and Captain Kater, who were so appointed, and who had previously been Resident Commissioners under the Act, immediately refused the situations. Dr.
Young became one of the Advisers; and Captain Sabine and Mr. Faraday were appointed by the Admiralty as the two remaining ones. Of Dr. Young, who died shortly after, I shall only observe that he possessed knowledge which qualified him for the situation.
Whether those who at present fill these offices can be said to belong to that cla.s.s of persons which the Order in Council and the Act of Parliament point out, is a matter on which doubt may reasonably be entertained. The Order in Council speaks of these three persons as being the same, and having the "SAME DUTIES" as 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 p.r.o.nounce 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 circ.u.mstance 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 mult.i.tudes 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 cla.s.s 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 circ.u.mstances, 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 Inst.i.tute 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 n.o.body will attend; its medals have lost their l.u.s.tre; and even the Inst.i.tute 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 pa.s.sage of any star between the several wires; supposing the distances of those wires equal, the intervals of time occupied by the star in pa.s.sing from one to the other, ought to be precisely the same. As those times of pa.s.sing 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 quant.i.ty registered, the agreement becomes more probable than if tenths were the smallest quant.i.ties 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 pa.s.sing the wires were only registered to the nearest minute, the intervals would almost certainly be equal.
There is another circ.u.mstance, 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 repet.i.tion 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 lat.i.tudes 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 circ.u.mstance 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 lat.i.tudes 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 repet.i.tion."
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 circ.u.mstance of some doubts having been entertained respecting the value of the principle of repet.i.tion.
The following series of observations were made with the two instruments.
[I have chosen the inferior meridian alt.i.tude of Polaris, merely because the number of sets of observations are rather fewer. The difference between the extremes of the alt.i.tude of Polaris, deduced from sets taken above the pole by the same observers, amounts to seven seconds and a half.]
Lat.i.tude deduced from Polaris, with a repeating circle, 16 inches diameter.--BASE DU SYSTEME METRIQUE, tom. iv. p. 376. 1807.
Number of Lat.i.tude Names of Observers.
Observations. of Formentera.
deg. min. sec.
64 38 39 55.3 Biot 100 54.7 Arago 10 56.2 Biot 88 56.9 Biot 120 56.7 Arago 84 54.9 Biot 100 56.5 Arago 102 57.1 Arago 80 54.5 Biot 88 53.3 Arago 90 53.6 Arago 88 53.8 Arago 92 53.7 Arago 42 55.6 Chaix 90 54.1 Chaix 80 53.9 Arago
Mean of 1318 Observations, 38deg. 39min. 54.93sec.
Sets of Observations made with a six-inch repeating circle, at Maranham.
Star. Number of Lat.i.tude Observer.
Observations. deduced.
deg. min. sec.
alpha Lyrae 8 2 31 42.4 Capt. Sabine alpha Lyrae 12 43.8 Ditto alpha Pavonis 10 44.5 Ditto alpha Lyrae 12 44.6 Ditto alpha Cygni 12 42.1 Ditto alpha Gruris 12 42.2 Ditto
Mean lat.i.tude deduced from 66 observations 2deg. 31min 43.3sec.
In comparing these results, although the French observations were more than twenty times as numerous as the English, yet the deviations of the individual sets from the mean are greater. One second and three-tenths is the greatest deviation from the mean of the Maranham observations; whilst the greatest deviation of those of Formentera, is two seconds and two-tenths. If this mode of comparison should be thought unfair, on account of the greater number of the sets in the French observations, let any six, in succession, of those sets be taken, and compared with the six English sets; and it will be found that in no one instance is the greatest deviation from the mean of the whole of the observations less than in those of Maranham. It must also be borne in mind, that by the lat.i.tude deduced by the mean of 1250 superior culminations of Polaris by the same observers, the lat.i.tude of Formentera was found to be 38deg. 39min 57.07sec., a result differing by 2.14sec. from 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 p.r.o.nounced 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 10.9sec. This circ.u.mstance 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 lat.i.tudes as corrected for the error of level:
Station. Star Lat.i.tude Lat.i.tude Diffe- by Capt. corrected for rence Sabine error of level.
deg.min.sec. deg.min.sec. sec.
Sierra Leone Sirius 8 29 27.9 8 29 34.7 6.8
Ascension Alph.Centuri 7 55 46.7 7 55 40.1 6.6
Bahia Alph.Lyrae 12 59 19.4 12 59 21.4 2.0 Alph.Lyrae 21.2 58 49.8 31.4 Alph.Pavonis 22.4 59 5.1 17.3
Maranham Alph.Lyrae 2 31 42.4 2 31 22 20.4 Alph.Lyrae 43.8 31.8 12.0 Alph.Pavonis 44.5 44 .5 Alph.Lyrae 44.6 42.6 2.0 Alph.Cygni 42.1 39.2 2.9 Alph.Gruris 42.2 27.4 14.8