REMARKS ON THE MAPS. 
669 
far the greater portion of the countries over which Dr. 
Earth's labours extend, was laid down either from dead 
reckoning or from computations of native routes and native 
information. Thus the Avhole route from Zinder to Tim- 
buktu, for example, a distance by Dr. Earth's travelling lines 
of upwards of 1200 English miles, had to be laid down solely 
from dead reckoning taken from a very accurately kept 
journal; and the magnetic variation had to be guessed at. Yet, 
despite of these shortcomings, the writer hopes that in the 
construction of these maps, in several of which he was greatly 
assisted by the original maps laid down by the traveller him- 
self, he has not departed very widely from the truth ; and he 
looks confidently forward to their being tested by the Niger 
expeditions. 
A great deal has been said of late on astronomical obser- 
vations in connection with African exploration, and it has — 
in some instances — been represented as if only those travels 
and explorations which were based on such observations were 
valuable, while all others were of no value. Assertions made 
thus indiscriminately are most objectionable, as a careful 
noting of the bearings and distances of each day's journey, 
such as Dr. Earth has made, is far preferable to many 
astronomical observations which cannot be implicitly re- 
lied on ; it is only the accurate astronomical observations 
which deserve to be regarded as well established points in a 
traveller's route. In our own case we could adduce many 
striking instances of the uncertainty of occasional observa- 
on west side of lake. (See tlie Journal and the Proceedings of the Royal 
Geographical Society of 1854 — 1858. But in the Journal, vol. xxv. 
p. 242., there is a misprint, the latitude of Kiikawa being given as 
12° 15' 14'^) 
Mr. Overweg's latitudes, besides his observation at Belarigo (14° 50' 0'' 
long., 13° 26' 37" lat.), relate to the following places : Mizda, Tabonieh, 
El Hasi, Wadi Ajunjer, Falesselez, Aisala, Tin-tellust, A'mfisas, island of 
Guria in the Tsad, and on his route to the Miisgu country, Yedi, Marte, 
Alia, Del-he, Zogoma, Masa, five other intermediate stations, and three 
observations in the district of Wulia. (See Petermann's account, p. 15.) 
