From Joag we accompany Mr. Park to Kooniakarry and Jarra. The reckoning between the two first gives about 23¼ min. difference of latitude, 55 of easting.[69] And hence the latitude of Kooniakarry will be 14° 48′ by account; but the observation taken at Jumbo, in its neighbourhood, giving only 14° 34′, the account is 14 to the north; equal to about a point and quarter in bearing. The same mode of correction has been applied here, as in the former part of the route; that is, the whole distance has been (for the present) allowed; with the difference of latitude by observation; and hence Kooniakarry will fall 59½ geographic miles to the east of Joag.
The route from Kooniakarry to Jarra[70] may be divided into two parts; first, to Feesurah, a place of observation, south-eastward; and secondly, to Jarra, north-eastward.
The account to Feesurah agrees very nearly with the bearings and distance. The latitude by observation was 14° 5′, and the easting from Kooniakarry, corrected, 47 miles. Then, to Jarra, the account also agrees very nearly; the latitude was 15° 5′, that is, just one degree north of Feesurah; and the easting from thence 33 miles.
The aggregate of easting, between Joag and Jarra, is then 139½ miles.[71]
It may be observed, that throughout this journey, generally, the reckoning has been to the northward of the observations; and that, by about ten degrees on the whole traverse, when 17 degrees of variation have been allowed. It will hardly be supposed that the difference arises from allowing too much variation by ten degrees; but it is singular, that the error should, in all cases but one, lie the same way. I do not by any means regard the error as considerable, circumstances considered:[72] nor is it of any consequence in the parts where the observations of latitude serve to correct it: as between Pisania and Jarra.
Mr. Park was plundered of his sextant at Jarra, which accident of course put an end to his observations of latitude; and thus, unfortunately, left the remaining half (very nearly) of his geography in a state of uncertainty, as to parallel. This point, therefore, must be regarded as the most advanced geographical station, that rests on any certain basis of parallel. However, the remaining part of the route will not appear to be much out, when it is seen how nearly the bearing of Sego, as determined by Mr. Park, agreed with the line of direction pointed out from Jarra.
It is, no doubt, a favourable circumstance, that the instrument was not lost at an earlier period, and before the commencement of the intricate route between the pass of the Senegal river and Jarra; to which may be added, the advantage of a known parallel, from whence to set off the very important bearing of Tombuctoo. In effect, the bearing was pointed out from Benowm, but this place being nearly east from Jarra, and the bearing in question E ½ N, no error of any magnitude can be looked for.
Jarra (called also Yarra), has already appeared in the Maps drawn for the Association, and was originally taken from M. Delisle’s Map; but was neglected, or overlooked, by M. D’Anville. In the former Map it was placed somewhat more to the west, and in a higher parallel by about ¼ of a degree.
Between Jarra and Wassiboo, Mr. Park’s reckoning, as it appears wrought up in his table of day’s works, gives 41 min. diff. of latitude N, and 1° 31′ diff. longitude E; which reduced to departure, in miles, is 89, and produces a course of E 26° S. But he allowed no variation after he left Jarra: and as I allow 17°, the course must be taken at E 9° S, distance 96½ geographic miles. From this arises a diff. lat. of 16′ only; departure 95: and, hence, Wassiboo should be in latitude 14° 49′, and 95 east of Jarra.[73]
Mr. Park was so lucky as to preserve his original bearings,[74] between Wassiboo, and Diggani (a place about 15′ short of Sego); and these alone, out of all that were taken during the route. These give a course of E 27°½ S, 174 geographical miles; so that when 17° of variation are allowed, the true course will be E 10½ S; the diff. lat. 31,7; departure 171,1; whence Diggani should be in lat. 14° 17′, and 266,1 east of Jarra.