IN CENTRAL AFRICA. 303 
shadow which he took at Timbuctoo itself. This obser- 
vation was made by the same method as that at Time : 
this proceeding is undoubtedly very imperfect, but, for 
want of others I think it should not be entirely neglected. 
On the 1st of May 1828 our traveller planted a style of the 
height of 0, 635 metre ; he measured, at noon, the shadow 
of this style and found it equal to O, 030 metre.'* The 
calculation gives seventeen degrees fifty one minutes 
north latitude. 1 must repeat here the reflection that 
this agreement may very probably result from contrary 
errors which have balanced each other : but as it is impos- 
sible to discover the points in which the errors lie, or the 
limit of their extent, the final result is all that can be ob- 
tained. 
I will add one consideration which will not have 
escaped those geographers who have studied the calcula- 
tion of probabilities. In a series of observations made un- 
der the same circumstances, and especially by the same 
observers, the greater the number, the more probable is 
it that their amount will approach to the total quantity re- 
quired. When there is no reason that the errors commit- 
* Zenithal distance from the superior edge of 0 2^ 26' 
Semidiameter of © 0 16' 
2 
42 
North latitude 17 
51 
I must not conceal the fact that M. Caillie made four similar ob- 
servations in different places, which are too inconsistent with the itine- 
rary to be made any use of. 
