APPENDIX. xliii tries in general, there are so many things to obstruct a direct track, that, though an animal may actually pass over the ground at the rate of three or three and a half miles per hour, as the camel in reality does, yet, in estimating the distance for a traverse-table, great deductions must be made, or our reckoning will far exceed the truth*.

The journey round the Syrtis having satisfied us with respect to the rate which might be allowed, and the accuracy that was to be expected under general circumstances, we determined to ascertain what precision we could arrive at when the direction of the road and nature of the ground were the most favourable. For this purpose we kept a track from Bengazi to Ptolemeta ; and having occasion to go over the same ground a second time and return, we had three measurements between the places independent of that of the chronometers which, as well as those of the intermediate stations, agree together and with the truth, to an exactness which we did not expect ; and will serve to show that, under favourable circumstances, and when attention is paid to the rates of the camels, the topography of a country may be laid down sufficiently accurate for most purposes. We should have informed our readers, that the track from Bengazi to Ptolemeta is particularly straight, and encumbered with as few obstructions as are likely ever to occur in a country where, properly speaking, no road exists.

* In caravans where the road lies over a wide expanse of desert, and where it is the interest of every man to accomplish as much distance in a day as he can, the average will of course far exceed that which was made good by our party, t See the Table annexed.