both (an addition of 3° Centigrade should be made to the temperature
recorded by Barth at midday from May to August).
Mon. avg.: Monthly Average.
Avg. snr.: Average of readings at sunrise.;
Avg. 2 p.m.: Average of readings at 2 p.m.;
Hst. fl.: Highest fluctuation in daily temperature.
Avg. 12-1 p.m.: Average of readings from 12-1 p.m.
Avg. 1-2.30 p.m.: Average of readings from 1-2.30 p.m.]
+------+------------------+------------------------+-------------+----+
| | Nachtigal’s | Barth’s Observations. | | |
| | Observations. | Degrees in Centigrade. | | |
| | Degrees in | (Those given in | Approx. avg.| |
| | Centigrade. | Fahrenheit reduced | |Mon.|
|Month.| | to Centigrade.) | |avg.|
| +-----+------+-----+-----+-----+------+-----+------+------+ |
| |Avg. | Avg. |Hst. |Avg. |Avg. | Avg. |Hst. | Avg. | Avg. | |
| |snr. |2 p.m.| fl. |snr. |12-1 |1-2.30| fl. | snr. |1-2.30| |
| | | | | |p.m. | p.m. | | | p.m. | |
+------+-----+------+-----+-----+-----+------+-----+------+------+----+
|Jan |18·9 | 30 |16·2 | 15 | 35 |33 (?)| 24 | 17 | 32 |24·5|
| | | | | | | | | | | |
|Feb | 19 | 30·2 |16·1 | 15 | 31 | 35 | 19 | 17 | 33 | 25 |
| | | | | | | | | | | |
|Mar | | | | 21 | 37 | 36 | 16 | 21 | 36 |28·5|
| | | | | | | | | | | |
|Apr | | | | 25 | 37 | 43 | 18 | 25 | 43 | 34 |
| | | | | | | | | | | |
|May | | | | 23 | 40 | | 17 | 23 | 43 | 33 |
| | | | | | | | | | | |
|Jun | | | | 24 | 37 | | 20 | 24 | 40 | 32 |
| | | | | | | | (?) | | | |
| | | | | | | | | | | |
|Jul | | | | 24 | 31 | | 9 | 24 | 34 | 29 |
| | | | | | | | | | | |
|Aug |23·3 | 29·3 | 9·2 | 22 | 30 | | | 23 | 31 | 27 |
| | | | | | | | | | | |
|Sep |24·1 | 31·4 |10·8 | 22 | 31 | 36 | 11 | 23 | 34 |28·5|
| | | | | | | | | | | |
|Oct |24·5 | 35·5 |16·1 | 24 | | 36 | 15 | 24 | 36 | 30 |
| | | | | | | | | | | |
|Nov | 20 | 33 |16·5 | 16 | | 32 | 27 | 18 | 32 | 25 |
| | | | | | | | | | | |
|Dec |18·5 | 30·4 |16·3 | 12 | | 31 | 26 | 15 | 31 | 23 |
+------+-----+------+-----+-----+-----+------+-----+------+------+ |
| Yearly average of temperature measured at | | | |
| sunrise and at 2 p.m. | 21 | 35 | |
+--------------------------------------------------+------+------+----+
| Total yearly average | 28°|
+----------------------------------------------------------------+----+
Naturally the conditions for the northern and southern parts of Bornu
vary somewhat, and local circumstances may also cause quite considerable
fluctuations of temperature. Thus I noticed at Idjege in Southern Bornu,
at the beginning of October, that the granite masses thickly studded
with trees, on the slopes of which the place lies, had the result of
causing an unusual increase in heat, which close to the surface of the
soil measured 51° centigrade in the shade. While the nights here were
even oppressively hot, a few days later on the plain at Dissa, not far
from Idjege, the thermometer only showed 10° centigrade in the morning
before sunrise, and by so doing registered the lowest degree of
temperature, whose fluctuations far exceeded 30°. In general the heat
reaches its highest point about 2 p.m. and then only declines very
slowly, so that even in the evening abnormally high temperatures may be
registered,[122] in fact the interesting phenomenon may occasionally be
observed of a higher temperature at sunset than at midday.[123] If one
takes the yearly average temperature according to Barth’s and
Nachtigal’s tables, one cannot but notice that Nachtigal’s tables leave
out of consideration just the hottest months. Having regard to this
circumstance, one may reckon without much inaccuracy the yearly average
temperature at from 29° to 30° centigrade.[124]
With regard to the second most important factor in the climate, viz. the
winds, there exist no such detailed observations as with regard to the
temperature; still the facts communicated on this subject by Nachtigal
and recent French explorers, especially Foureau,[125] are sufficient to
show that just as the atmospheric pressure is extremely regular so
likewise are the winds. During the greatest part of the year, under the
influence of the north-east trade-wind, north-easterly or easterly winds
predominate, but south of 12° north latitude, where the wind comes
mostly from the south with a decided inclination towards the south-
east,[126] it is less constant, a fact which Foureau attributes to the
counter-influence of the south-east trade-wind which reaches as far as
here.[127] According to the universal verdict of all observers, easterly
and north-easterly winds predominate especially in the dry weather,
while in the rains, especially in July and August, westerly winds gain
the upper hand, only to surrender their predominance to the easterly
winds in October.
Views as to the daily fluctuation in the strength and direction of the
wind appear to vary. Unfortunately Nachtigal’s tables[128] do not inform
us whether observations with regard to the wind were taken also at
night-time. The French naval officer Audoin, who personally took
observations of this sort on Lake Chad, where the conduct of the watery
plain is bound to give indications conformable to every movement of the
wind, lays stress on the predominance of the north-east wind, especially
from 11 p.m. to 9 a.m., while it is replaced by the south-west wind for
the rest of the day.[129] The north-east trade-wind brings with it from
the Sahara a great volume of dust, which often renders the atmosphere so
opaque that the sun only appears through it like a dark-red disk. This
phenomenon, which causes a peculiarly oppressive sensation,[130] is
known throughout the whole of Western Tropical Africa under the name of
Harmattan, but is especially characteristic of the Central Sudan.
Apart from the violent atmospheric disturbances which the tropical
thunderstorms bring with them, the cyclones or tornadoes, coming
sometimes from the south-east, sometimes from the north-east or south-
west, especially during the times of the change in the wind, affect
Bornu as well as the whole tropical district of the Western and Central
Sudan.
In Bornu, where over wide stretches of country the weakening effect of
dense forests is lacking, they attain an unparalleled violence. They
give notice from afar of their arrival by thick clouds and whirling
dust, and sweep everything off the earth that has not been made trim and
taut. Sometimes cornfields which have been overtaken by them look as if
a roller had passed over them. During the autumn of 1903 the roofs of
the houses at Dikoa were blown off by a violent tornado. In general the
cyclones are not preceded by discharges of electricity, but there are
exceptions to this rule.
The tornadoes may be matched in violence by the thunderstorms which
occur in Bornu. As is often the case in the tropics, they are heralded
beforehand by the discharge of a large amount of electricity, a
phenomenon which it is especially fine to observe at night, when the
lightning flashes following each other uninterruptedly render it
possible to read a book.[131]
Whilst on the subject of hydrometry, the question of cloud formation has
next to be considered. The sky in Bornu, quite apart from the Harmattan,
is very seldom quite clear; it is only in winter that there may be
several successive days free from clouds; at other times ‘cirrus’ clouds
at any rate are perceptible. The most wonderful cloud formations can be
observed at the transition period shortly before the bursting of a
thunderstorm. The results are analogous to those prevailing in Europe
under similar circumstances; only in the Central Sudan the ‘cumulus’
formations differ in being grander, and they discharge themselves more
quickly.
Fogs occur, but they are chiefly confined to the cooler parts of the
year, and usually, as in northern latitudes, are connected with the
presence of swampy districts, such as the damp low-lying shores of Chad.
Besides it would be difficult, especially in the cooler morning hours,
to distinguish sharply between fog and Harmattan.
Bornu lies exactly in the zone of the tropical summer rains, whose
northerly boundary, naturally not to be sharply defined, coincides
roughly with the fifteenth parallel of latitude, and thus includes also
the most southerly part of the Sahara.[132] The moisture that falls
there is only in the form of dew and rain. The mountains which border
the country are not high enough to favour the formation of hail, which,
however, is often enough to be seen in the neighbouring highlands of
Central Adamawa and the grass-lands of the Kameruns that lie to the
south of them. Dew appears—though only seldom—chiefly in September,
October, and March; but then usually in profuse volume. Thus Denham in
March and Barth in September experienced a quite extraordinarily heavy
dew on the banks of Lake Chad, which they thought worthy of particular
mention.[133]
The weather conditions accompanying the beginning or end of the rains
usually occur with great regularity in Bornu. In this respect the
country shows the typical Sudan climate, which is generally entirely
without rain during the months of November, December, January, and
February. The only noteworthy exception appears to be the actual borders
of Chad. On the evening of the 22nd of January, an unusually cool day,
and on the following morning, in the immediate vicinity of Chad, Foureau
notes violent showers of rain, which were preceded in the afternoon by
slight showers with some thunder and lightning.[134]
The rainfall is influenced in two different ways by the mountains on the
southern border. Firstly, the volume of rain that falls here—though
proper measurements of it have hitherto not been forthcoming—appears to
be more intense than in the plains; and, secondly, the rains here set in
earlier and do not end till later.[135] A greater or lesser distance
from the Equator operates in a similar way. For the further south one
goes, the longer is the duration of the rainy season and the greater the
volume of the rainfall.
Apart from the above-mentioned exceptions, the first drops of rain do
not fall in Bornu before the end of March. The downpour is heaviest in
July and August. Though many of the tornadoes are extraordinarily severe
and long-continued, yet the rain never lasts without intermission for a
whole day or even a week, as it may do in the primaeval forest region of
the Kameruns.[136]
In spite of the low rainfall as compared with that of Adamawa, which
lies to the south of it, the climate of Bornu, except in the dry
weather, thanks to its low-lying marshes, is distinctly unhealthy.[137]
Besides the diseases, such as dysentery, which appear at all times of
the year, malaria and its attendant evils are chiefly prevalent during
the rainy and equinoctial seasons; Europeans especially are subject to
it to an unusual extent, as are also the Arabs and Berbers accustomed to
the healthy climate of the desert.[138] But even the natives are not
entirely exempt from such diseases, which may assume the form of
devastating epidemics.[139] The only part free from fever seems to be
the uninhabited belt of marshy vegetation round Lake Chad, because
infection from man to man is here impossible, although there are clouds
of mosquitoes ready to convey the germs of the disease. On the same
grounds the larger towns, which scorn all sanitary regulations, are the
worst centres of disease. The irritant microbe which lives in the
anopheles mosquito is paralysed at a temperature below 17° centigrade,
and consequently dies during the cold nights of the dry weather, in the
event of its host not spending the night in the warmth of a house.
The rainy season in Bornu is dreaded by the Berbers or Tripoli Arabs not
only on account of the danger to their own health, but the condition
also of the pack-camels bred in the Sahara is influenced very
unfavourably by it, in fact it sometimes causes great mortality amongst
them, so that the caravans, whenever they can, leave the country at the
beginning of the damp weather.[140] It is not yet certain whether the
camels fall victims to the same disease from which the animals bred in
Bornu, horses and especially oxen, have to suffer. Inquiries into the
question of whether it is spread in the form of a contagious disease
like trypanosomiasis—the disease whose germ is conveyed by the tse-tse
fly—have not yet been published, but at any rate myriads of flies
belonging to the ‘Glossina’ species are to be found in the neighbourhood
of the water-courses fringed with trees and bushes.
It is obvious that the moist heat of the rainy season is favourable to
the growth of all kinds of sickness. Besides venereal disorders,
malignant eye-diseases are very common, and, owing to the indolence of
the natives, find every chance of being spread abroad; leprosy is by no
means unknown.[141] One of the commonest evils is that caused by the
guinea-worm, a skin-disease which, though not dangerous, is protracted;
the worm enters the body through the use of unboiled water from puddles,
water-courses, and even from wells, and almost every native has been
attacked by it at some time during his life.[142] Cleanliness and the
scrupulous observance of simple rules of health, including especially
regular bodily exercise, afford, however, far-reaching protection
against all these diseases, not excluding malaria itself, so that at any
rate Europeans can secure themselves in some degree against sickness.
All these districts are at all events far from being so unhealthy as the
region of the West African primaeval forest, where the germ-destroying
effect of the sun’s rays seldom penetrates.
[Footnote 118: Barth, to whom the conditions of temperature at Massawa
were not yet known, even asserts that ‘the average summer temperature of
Kukawa exceeds that of any other place on earth’. Barth, iv. 12. [To
bring degrees centigrade to degrees Fahrenheit multiply by 9 and divide
by 5 and add 32.]]
[Footnote 119: Cf. Barth, iv. 12, where Barth refers to ‘the coldest
night of his whole journey’, and mentions that the temperature shortly
before sunrise was only 4·5° centigrade above freezing-point. The Yola-
Chad Boundary Commission repeatedly experienced similar cold nights in
the winter of 1903-4, and the native carriers suffered severely from
them.]
[Footnote 120: Certain trees, e.g. the sappy _Candelabria-Euphorbia_,
exhibit in their shade a temperature differing some three or four
degrees from that of their surroundings. I can testify that this was so
at Madagali, in the Mandara highlands, where my tent was pitched under a
very large _Euphorbia_. The temperature in the open tent, on the
contrary, did not differ from that outside.]
[Footnote 121: At the end of this month Barth registered 45° centigrade
in Bornu. Barth, v. 406.]
[Footnote 122: In the very south of Bornu Stieber was able in March to
observe temperatures which dropped from 45° centigrade at 8 p.m. to 30°
centigrade. _Kolonialblatt_, XVI. Jahrgang, p. 88. Cf. also Denham, i.
150.]
[Footnote 123: Barth, iii. 625. On April 12 at 1.30 p.m. the thermometer
stood at 35° centigrade, at sunset it was 37·3° centigrade.]
[Footnote 124: [Vid. Appendix VIII.]]
[Footnote 125: _Doc. sc._, i. 128.]
[Footnote 126: [Vid. Appendix VIII.]]
[Footnote 127: _Doc. sc._, p. 81.]
[Footnote 128: Nachtigal, ii. 766.]
[Footnote 129: _La Géographie_, vii. 317.]
[Footnote 130: [On the contrary, most people find the Harmattan tonicky
and exhilarating. Cf. article by Seefried in ‘M. Deutsch. Schutzgeb,’ 26
(1913) 9-12].]
[Footnote 131: Other electrical appearances connected with thunderstorms
have not yet been observed, but Lenfant mentions seeing the Zodiacal
Lights for several days in the winter. Lenfant, p. 285.]
[Footnote 132: Nachtigal, i. 558; ii. 193 and 315.]
[Footnote 133: Denham, i. 120; Barth, iii. 23 (German edition).]
[Footnote 134: Foureau, _D’Alger au Congo_, p. 622, and _Doc. sc._, i.
133. I can myself confirm that rain occurs on Chad at this time of the
year, for on a ride from Maduari to Kukawa on the very cool morning of
January 15, 1904, I travelled for a short distance in a tornado.]
[Footnote 135: Cf. Rohlfs, ii. 14.]
[Footnote 136: [For rainfall in British Bornu vide Appendix VIII.]]
[Footnote 137: [Bornu is one of the healthiest Provinces of Nigeria.]]
[Footnote 138: Cf. _idem_, ii. 89.]
[Footnote 139: Nachtigal, i. 733; cf. also ii. 488.]
[Footnote 140: Denham notices the insalubrity which accompanies the
rains with the words: ‘All the quadrupeds, as well as bipeds,
transplanted from the countries bordering upon the great ocean appeared
to suffer alike,’ i. 264; cf. also Nachtigal, i. 681.]
[Footnote 141: [Lepers in British Bornu are now concentrated in two
leper-camps under the supervision of the Government Medical Officers.
Average numbers in Maiduguri leper-camp 950, in Geidam 120. They are
housed, fed, and clothed by the Beit-el-Mal (Native Treasury). These
figures do not include the pagan districts.]]
[Footnote 142: [Intestinal worms are also very common, especially among
the cattle-owning Shuwas.]]
V
FLORA
The flora of Bornu corresponds exactly to the geological formation and
climatic conditions of the country.[143] The usual appearance of the
country is that of a tree-covered steppe, which extends south of the
border-line of the regular summer rains over the vast plains of the
interior of Africa from somewhat north of 8° of north latitude, from
Senegal to Cape Guardafui, east of the great Central African lake and
reaching southwards as far as South-East Africa. The character of this
steppe is dependent on the predominance of deciduous plants, mostly
belonging to the order of Leguminosae, and of many thorny trees and
bushes, which very gradually give way on the borders of the country,
according to local conditions, to representatives of the flora of the
desert, of the damp tropical uplands or of the primaeval forest
district, or else are found intermingled with them. Whilst Bornu shows
in the north over a wide extent somewhat more luxuriant examples of
species belonging entirely to the flora of the desert, on its own side
also it spreads plants peculiar to itself pretty far into the south of
the Sahara, but it lacks representatives of the above-mentioned grass-
lands and primaeval forest flora owing to the predominance of evergreen
trees and the appearance of epiphytic vegetation. Nowhere in Bornu can
one find the dark-green forests with their hot-house humidity and tree-
loving ferns, orchids,[144] and begonias, with pandanacea and different
kinds of climbing calamus, with raphia- and oil-palms, which in dense
lines edge the water-courses of the grass-lands lying not much further
south. Of plants which are peculiar to such districts, the banana is
only to be found at one place in the country, and that curiously enough
is at Zinder, in the north-west corner of the country, whither it must
evidently have been introduced from outside.[145] The raphia-palm,
_Raphia vinifera_, and different varieties of paw-paw[146] first appear
on the southern edge of the Mandara mountains, which lie scattered to
the south of the tenth parallel of north latitude, and only one variety
of _Ceiba pentandra_, which is indeed stunted enough in comparison with
the specimens of giant Ceiba (_Bombax_) of the West African primaeval
forest, is to be found here and there in the neighbourhood of the water-
courses. There are indeed the trees of the Ceiba species, which, in
contradistinction to the evergreens, shed their leaves in the dry
weather—even in the primaeval forest. It appears rather strange that
none of this kind of vegetation occurs along the course of the Lower
Shari, which is always full of water, although it is plentifully
represented at the sources of that river, especially the Gribingi,[147]
and although it extends for a short distance down-stream close to the
banks. The reason of this phenomenon may perhaps be sought for in the
fact that the long and intensive dry weather of Bornu, and also of the
Lower Shari country, is not favourable to this kind of vegetation. This
is analogous to the similar phenomenon on the Upper Nile, where the
plant formation of the hot damp countries where the river rises extends
through districts which get drier and drier as one proceeds northwards,
but cannot advance at all after the latitude of Khartum.
The sole or at any rate predominant landscape as regards Bornu, so far
as it depends on the flora, is just this tree-studded steppe.[148] Even
the trees are in unison with this steppe; if they do not belong to the
prevailing species of acacia, they are at any rate of a habit in
accordance with them. They are in general low, stunted and twisted, with
deep roots and wide-spreading crowns, not higher than the trunk of a
twenty-year-old oak sapling; only along the water-courses and where a
deep layer of ‘humus’ soil exists do they reach a more considerable
height, but even in the most favourable spots they do not much exceed 25
metres. The density with which the trees are planted depends also on the
condition of the soil. Generally the trees stand in high steppe-grass at
such long intervals that their crowns hardly touch, then the landscape
reminds one of the extensive fruit-tree plantations of the north. The
better the soil is, the closer stand the trees and thus form dense wide-
spreading forests, often tangled with creepers, as for example in the
riverain district of the Lower Shari from Karnak to Lake Chad.[149] In
other places, especially on the granite slopes of the hills that jut out
into the Bornu plain, the trees occur so far apart, that the landscape
comes to show a great similarity with the slopes of the Sierra Nevada
covered with sparse ilex trees which dip down to the Rio Genil in
Southern Spain. In fact, where the true tropical trees, such as the palm
and fig species, or the strange-looking ‘kuka’ (Adansonia) are wanting,
the general impression of the flora is quite that of Northern Europe.
Often, especially in winter when the ground is covered with fallen
leaves, one can find places that at once recall the tree-bordered river
valleys of the low-lying plains of North Germany in autumn. Localities
which give a regularly tropical impression are at all events not in the
majority, and the inspired descriptions of tropical luxuriance which
Nachtigal gives on his first acquaintance with these parts, originated,
as he himself has to admit, from the impression of dissimilarity between
the Chad countries and the Sahara through which he had just
struggled.[150]
By far the largest number of characteristic trees and bushes are
naturally of such a stamp as are suited to the conditions of the
country. The arrangements designed for the preservation of species are
the thorny spikes for defence against annihilation by things that feed
on them or for protection against drought during the winter months. Most
of the trees shed their leaves in the dry weather, but those that do
not, possess a quantity of thick leathery foliage or fine feathery
leaves, succulent twigs, tendrils with tough outer fibre or thick cork-
like bark. On the shea-butter trees, _Butyrospermum Parkii_, and the
ilia-acacia, _Burkea africana_, and especially on the timber found in
Southern Bornu, this thick cork-bark is to be observed, serving at the
same time as a protection against the ‘bush’ fires.[151]
Soon after the beginning of the dry weather the high grass is quite dry,
and affords ample material for the ‘bush’ fires that now commence. The
trees and bushes, sticking out of the burnt, ash-covered soil with their
bark all charred, offer then a melancholy spectacle. This may make them
appear as if quite dead, but as a matter of fact the bark, of which only
the outer layers have been burnt, has been able to protect the sap so
well, that just before the beginning of the first rains tree and bush
put forth fresh leaves and twigs or even stand dressed in full
bloom.[152] About the beginning of January the Leguminosae begin one by
one to bloom, and shortly afterwards the other trees and shrubs follow
suit, so that the ‘bush’ is soon pervaded with an overpowering perfume.