第 13 节
作者:铲除不公      更新:2021-02-21 16:01      字数:9322
  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