| In | 1720, | the longitude according to Delile | 0° | 0’ | Wt.of Paris |
| 1749, | d’Anville | 2 | 15 | ||
| 1790, | Major Rennell | 2 | 30 | ||
| 1796, | Park’s first map | 1 | 0 | ||
| 1805, | Park’s second map | 0 | 0 | ||
| 1821, | M. Walckenaer | 2 | 42 | ||
| 1821, | M. Lapie | 2 | 44 | ||
| 1822, | Clapperton | 0 | 50 | ||
| 1828, | M. Brué | 3 | 34 |
It is on the English maps, even those of most recent date, that this town has always been placed the most to the east. The advantage of a more eastern position relatively to the proximity of a great river flowing into the Gulf of Guinea would be evident: but this proximity is nothing less than certain. By a coincidence worthy of notice the English maps have also brought Timbuctoo farther to the south than any others except Delile, as will appear from this table of different latitudes:
| North latitude according to | |||||
| Delile | 15° | 0’ | Park’s second map | 16° | 27’ |
| Clapperton | 15 | 0 | M. Walckenaer | 17 | 38 |
| M. Lapie | 17 | 38 | |||
| M. Brué (after Clapperton) | 15 | 0 | D’Anville | 19 | 15 |
| Park’s first map | 15 | 14 | Major Rennel | 19 | 38 |
I return to the latitude of Timbuctoo. Ain-Salah, in the oasis of Touat, is usually placed about 1° east of Paris and in 24° 30’ north latitude; but Major Laing’s observation, as communicated to me by Captain Sabine, is very different, namely: 0° 29’ west of Paris, and 27° 11’ 30". M. Walckenaer has calculated the distance from this oasis to Timbuctoo at six hundred and seventy five geographical miles: it is evident that this measure, if admitted, would advance Timbuctoo towards the north to between the 17th and 18th degree; now, it happens that this distance of six hundred and seventy five miles is found exactly between the two points as placed upon the present map. This last coincidence, which I remarked after my labour was concluded, contributed still farther to dispel my doubts. I have estimated the day’s journeys at 18’ four tenths and not with M. Walckenaer at 15’; but it was the medium journeys, not those of the great caravan, which formed the object of his researches. It appears then that the approximative situation assigned to Timbuctoo, 6° west and 17° 50’ north, satisfies the different data, and the best itineraries, that it agrees with the positions of Timbo and of Fez, and that it is not contradicted by Mungo Park’s observations on the latitude, taken at Sami and Yamina; finally, it is confirmed by the particulars brought from Elimané by Captain Beaufort.
Fifty four days’ journeys will be found on my map from Timbuctoo to Tatta; an itinerary cited by M. Walckenaer (p. 297) marks fifty. The fifty four days from Fez to Timbuctoo according to Mr. Jackson[86] also agree: it is the same with the sixty-four days from Timbuctoo to Morzouk. Fewer than twenty eight journeys are reckoned from Houssa to Timbuctoo, according to the itinerary of Mohammed Ebn-Foul; this distance is too short on our map, and on all the others, even those in Clapperton’s travels. There are, besides, other reasons for believing that there may be two towns or countries called Houssa[87].
I do not compare with the map the distance reckoned between Timbuctoo and the town of Tafilet, because M. Caillié heard no mention of a town so called: he affirms that none such exists, in which case it is not possible to make use of this distance.
I shall add in conclusion of this discussion, that nothing can authorise us to depart from the observations of latitude taken by Mungo Park, at Yamina and Sami, namely, 13° 15’ and 13° 17’, and to remove these points much further to the south, as M. Brué has done upon his map, otherwise so rich in details and nomenclature. The determination which I propose for the latitude of Timbuctoo agrees better with these observations, the only ones we possess in this direction as far as Timbuctoo.
From the whole discussion, it results, first, that the different lines of route forming the itinerary map have been subjected to divers conditions resulting from the journal of the traveller, from anterior observations and from good geographical data; secondly, that the hour’s journeys, estimated at three English miles, mean measure, between Kakondy and Galia or Djenné, are a little increased between Kakondy and Timé, in consequence of the position of Timbo; thirdly, that, from Djenné to Timbuctoo and thence to Fez, the average of two miles an hour has been a little modified by the real difference in latitude of the two extremities. I have now only to speak of the bearings and measure of the lines of march.
BEARINGS OF M. CAILLIÉ’S ROUTES.
The reduction of the true north of our traveller’s lines of route was one of the most important points; and to arrive at their actual bearing, I was assisted by a single new datum only; namely, the observation of the angle of the meridian shadow with the magnetic north. The travels furnish two of these observations: the one, of the 30th of October 1827, gave the N. N. E.; the other of the 1st of November, the N. ¼ N. E., that is to say, the compass had on these days a declination of 22° 30’ and 11° 15’ to the east. I was then obliged to have recourse to other researches to determine between these two measures, and to avail myself of several observations taken by Mungo Park and other travellers.