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
