200 
NATURE 
| DecEMBER 27, 1906 
THE FRENCH SAHARA.* 
(1) FOUREAU has already told in a popular 
+ form the story of the expedition which he 
conducted with so much skill and success from the 
shores of the Mediterranean to the mouth of the 
Congo. Crossing the little-known country of the | 
Touaregs, making the circuit round Lake Chad, de- 
scending the Shira and Ubangi Rivers, he had ample 
opportunity for examining the French possessions in 
Africa, and studying the prospects of their future 
development. During the six years that have elapsed 
since his return from this expedition he has been 
engaged in arranging and discussing the scientific 
results, some of which are now presented to the 
public. The first and second fascicules give details 
of the astronomical and meteorological observations, 
with a description of the water systems, the topo- 
graphy of the district, and the geological action of 
local winds. It is fortunate that the atlas of maps, 
which are drawn on a very elaborate scale, accom- 
panies these handsome volumes. Since the geography 
of this part of Africa is somewhat uncertain, these 
are necessary in order to follow the exact route taken 
by the expedition. 
M. Foureau is well known as an African explorer. 
For nearly thirty years he has traversed the Sahara 
in all directions, but his ambition 
to penetrate to the Sudan _ has 
always been foiled by the action of 
the Touaregs. In his many expedi- 
tions he has naturally been assisted 
by the Government and by learned 
societies, but he has never had at 
his command a force sufficient to 
overawe this warlike tribe and to 
make himself independent of its 
assistance or good will. In 1898, 
by a fortunate accident, he found 
himself placed in a more hopeful 
position. Through a legacy from 
M. Renoust des Orgeries to the 
Société de Géographie, a consider- 
able sum of money became available 
for the purposes of exploration. 
The object of this bequest was to 
assist such expeditions as were 
undertaken with the view of bring- 
ing the independent tribes in the interior of Africa | 
under the influence or protection of France, and which 
should by pacific measures tend to weld into a homo- 
geneous whole the French possessions extending from 
Algeria to the Senegal and Congo. These funds were 
placed at the disposition of M. Foureau, who found 
himself in the autumn of 1898 at Wargla, at the 
head of a small army of some 300 men, a thousand 
camels, and the usual equipment of a well-organised 
expedition. M. Lamy, of the army of Algeria, was 
associated in the command of the expedition, and 
had charge of the military dispositions. | Unfortu- 
nately, this energetic officer and able colleague, 
whose very ready assistance is warmly acknowledged, 
lost his life in an encounter with the natives. | 
The astronomical observations would perhaps be 
more fittingly described as geodetical, since they are 
naturally limited to the determination of the position 
of stations. The observations were made by M. 
Foureau and Lieut. Chambrun. For his longitudes, 
the former relied mainly on the methods used at 
sea, supplemented by a few occultations and pheno- 
1 « 
Documents scientifiques de la Mission saharienne (Mission Foureau- 
Lamy d Alger au Congo par le Tchad).”” By F. Foureau. (1) Parts i. and 
ii., Observations, astronomiques et météorologiques. Pp. iv+ssr. (2) 
Partiii. Pp. 555-1210; with an atlas containing 16 maps. Geology, Petro- 
graphy, Palzontolocy, &c. (Paris: Masson and Co.. 1903-1905.) 
NOmUOsOn VOL.) 75] 
mena of Jupiter’s satellites. “Che author carried four 
available chronometers, and remarks that the error 
in longitude arising from the accumulated error in 
the rate of the chronometers during 102 days amounts 
to only seven minutes of arc. It is not quite clear 
how this seven minutes is reckoned, but it certainly 
implies excellent performance of the watches and 
great care in their manipulation. It should be added, 
too, that wherever a comparison between the longitudes 
derived by different methods is possible, the agree- 
ment is quite satisfactory. M. Chambrun trusted to 
equal altitudes of moon and stars, and transits of 
the moon across the meridian. The latter, like some 
of the lunar distances taken by M. Foureau, were 
not found to possess sufficient accuracy. For lati- 
tudes both observers measured the altitude of 
Polaris and meridian altitudes of sun and _ stars. 
These results call for no remark, though it is 
impossible not to admire the energy which enabled 
these observers to prosecute their work after the 
fatigues of hard travel. M. Foureau also made some 
measures of the magnetic declination and horizontal 
force. 
The meteorological or climatic observations are 
particularly welcome. These observations are, of 
course, spread over a large area, and it is not the 
climate of any one district that is presented. Con- 
Fic. 1.—Laige sand-dunes in the Erg region, Sahara. 
cerning temperature, the author remarks that the 
thermometer fell below zero (C.) twenty-five times, the 
minimum reading being —10°-2 (14° F.) at a height 
of 1144 metres. The highest temperature experi- 
enced was 48°.3 (119° F.), in March, t900. Through- 
out the region the minimum temperature occurs about 
5 a.m., and the maximum between 1 and 2 p.m, 
During the 645 days on which observations were pos- 
sible, the sky was entirely free from cloud on 132 
days, slight cloud was noticed on 227, while the sky 
was more or less overcast on 286. Dew was noticed 
on fourteen occasions, and rain fell on 116 days, but of 
these only forty-six were marked by severe storms; but 
violent atmospheric effects, whether of wind, or light- 
ning, or sandstorms, were of frequent occurrence. 
In the Air highlands, almost every afternoon the sky 
was blackened, while violent thunder and lightning 
were experienced. The entire horizon would be con- 
tinuously illuminated during whole minutes by 
brilliant flashes of lightning. Sudden hurricanes and 
appalling outbursts would keep men and animals in 
a state of tense excitement. Slight friction on the 
manes and tails of horses would bring forth, not 
electric sparks merely, but ‘‘ des nappes de lumiére.”’ 
The description of the Grand Erg and the character 
of the country through which the expedition passed, 
