The natives of Zanzibar distribute the year into five seasons. A far simpler division here applicable, as in Western India, is made by those local trades the monsoons, between whose two unequal lengths are long intervals of calms and of variable winds. These are the Mausim or N.E. monsoon, and the Hippalus or S.W.

1. The Kaskazi or Kazkazi (vulgarly Kizkazi), to which the Arabs limit the term El Mausim (Monsoon), is the season during which the Azyab (ازيب) or N.E. trade blows. The wind begins about mid-November; from mid-December to mid-February its strength is greatest, and it usually ends about mid-March. In 1857, however, the Kaskazi opened with light showers, and continued in full force till March 24; usually the last vessels from Cutch and Bombay enter port about March 10. This is the first of the two hot seasons, and midsummer may be placed in February and March. A fine, cool sea-breeze from the N.E. usually prevails between 8 a.m. and late in the afternoon. When it is absent the weather is sultry and oppressive, the northerner feels suffocated; the least exertion brings on profuse perspiration, and the cuticular irritation produces boils and ‘prickly heat.’ The nights are close and stifling enough to banish rest and sleep. As has been shown, the thermometer does not stand high, but the frequent flashes of sheet-lightning playing over the northern and western sky show a surcharge of electricity. The public health would suffer severely but for the frequent cooling showers which, especially at the end of the Kaskazi, are succeeded by several days of pleasant weather. This is the agriculturist’s spring. Sesamum, holcus, rice, and other cereals, are sown upon lands previously burned for manure. It is the traveller’s opportunity for visiting the interior of the island and the worst parts of the coast, but—‘bad is the best.’

2. The Msika (or Másika) Mku, Greater rain or rains. About the end of March the change of monsoon is ushered in by heavy squalls from the S.E. and by tornados blowing off land. Presently the Hippalus breaks, and extends from early May into October. In May native craft make India after a run of 20 to 25 days; after the end of August they rarely attempt the voyage. This Kausi or Hippalus is usually called S.W. monsoon, but it has mostly an eastern deflection, possibly modified by the westerly land-breezes. The Arabs divide it, as will be seen, into three portions. First, the Kaus proper,[[41]] in Kisawahili Kausi (قوسی), from mid-April to early August, the period of the greatest strength. Second, Kipupwe or first winter—July and early August; and third, the Dayman, which ends the Kausi.

Presently appear the rains which have followed the northing sun. The same observation was made by the Austrian mission on the White River in N. lat. 4° 30′. On the coast we can distinctly trace their progress. In 1857 the downfall began in Feb. 15, at Usumbara (S. lat. 5°), where the clouds are massed and condensed by a high plateau, leading to lofty, snow-capped mountains. In 1854 I found that the rainy season opened at Berberah of the Somal (N. lat. 10° 25′) on April 15; and in early June they reach Bombay (N. lat. 18° 53′). Concerning the movement of the wet season in inner intertropical Africa I have already written in the Journal of the Royal Geographical Society (xxix. 207).

The heaviest rains at Zanzibar Island begin the wet season about mid-April, and last 30 to 40 days; they do not end, however, till early June. Some observers remark that the fall is greatest at low water and during the ebb-tides of the Syzygies. It is, however, rare to have a week of uninterrupted rain, as in eastern India and sometimes in the Brazil. The discharge is exceedingly uncertain. Some years number 85 inches, others 108. During the first eight months of 1857 and the last four months of 1858, we find a total of 120·21 inches. In 1859 it reached 167, doubling the average of Bombay (76·55), and nearly trebling that of Calcutta (56·83). We may compare these figures with those of Europe and the United States. England has 31·97 inches; France, 25·00; Central Germany, 20·00; Hungary, 16·93; Boston, 38·19 (about the same at Beyrut in Syria); Philadelphia, 45·00; and St Louis, Mo., 31·97. Of these 167 inches (1859), 104·25 fell during the Msika Mku. The number of wet days ranges from 100 to 130 per annum. According to the people, rain has diminished of late years; perhaps it is the result of felling cocoas, and of disforesting the land for cloves. In 1857, the Great Msika was preceded by a few days of oppressive heat, which ended (March 24) in a highly electrical storm, like those which usher in the rains of western India, and suddenly the cool S.W. began to blow. For some time we had daily showers, now from the N.E., then from the S.W., with high winds and loud thunderings; the rains, however, did not show in earnest before April 10.

The islanders like the Msika to open with showers strong enough to bind the land, but not so violent as to carry off the manure deposited by the year’s decayed vegetation. After this the water should fall in heavy ropy torrents, with occasional breaks of sunshine and fine weather; when this lasts thirty days, and is succeeded by frequent showers, good crops are expected. The downfall is heavier in the interior of the island than about the city, which, situated upon a point, escapes many a drenching. It must, however, be borne in mind that the phenomena of the rains, like those of the sea and air, are essentially irregular. In some seasons there will be only half-a-dozen rainy afternoons; in others as many rainy mornings. There are years of great drought, and there are seasons when the sun does not appear for six weeks in succession. Usually heavy rain is not expected after 11 A.M., and showers are rare after 2 P.M. As I subsequently remarked in the east African interior—the Fluminenses of the Brazil still preserve the tradition—there is a curious regularity and periodicity in the hours of downfall, often extending over many days. This phenomenon may have done much towards creating the ‘rain-doctor.’

During the Msika the horizon is obscured, dangerously indeed for ships: the wind veers round to every point of the compass; the sky is murky and overcast; huge purple nimbi, like moving mountains, float majestically against the wind, showing strong counter-currents in the upper aërial regions. From afar the island appears smothered in blue mist, and often the cloudrock splits into two portions, one of which makes for the coast. Even during the rare days of sunshine the distances, owing to the continuous humidity, are rarely clear, and the exhalations make refraction extensive. A high tension of vapour is the rule. For the first three hours after sunrise the land is often obscured by ‘smokes,’ a white misty fog, often deepening to a drizzling rain; this lasts until 10 A.M., about which time the sea-breeze begins to blow.

The Msika is much feared by the native population, and the interior of the island becomes a hot-bed of disease. The animal creation seems to breathe as much water as air. The want of atmospheric weight, and consequently of pressure upon the surface of the body, renders the circulation sluggish, robs man of energy, and makes him feel how much better is sleep than waking. Europeans, speaking from effect, complain that the ‘heavy’ air produces an unnatural drowsiness—it is curious to see how many of our popular books make humidity increase the weight of the atmospheric column. During this season the dews of sunset are deemed especially fatal to foreigners. At times the body feels cold and clammy when the thermometer suggests that it should be perspiring: super-saturation is drawing off the vital heat. The lungs are imperfectly oxygenized, and, in general belief, positive is exchanged for negative electricity. The hair and skin are dank and sodden; indeed, a dry cutis is an unattainable luxury. Iron oxydizes with astonishing rapidity; shoes exposed to the air soon fall to pieces; mirrors are clouded with steam; paper runs and furniture sweats; the houses leak; books and papers are pasted together; ink is covered with green fur; linens and cottons grow mouldy, and broadcloths stiffen and become boardy.

This excess of damp is occasionally varied by the extreme of dryness. The hot wind represents the Khamasin of Egypt, the Sharki (or Sh’luk) of Syria, the Harmattan of west Africa, and the Norte of the southern Brazil, Paraguay, and the Argentine Confederation. At such times the air apparently abounds in oxygen and in ozone. Cotton cloth feels hard and crisp; even the water is cooled by the prodigious evaporation. Books and papers curl up and crack, and strangers are apt to suffer from nausea and fainting fits.

3. The Kipupwe, first winter or cold season—July and early August. The bright azure of the sky, the surpassing clearness of the water, and the lively green colours of the land, are not what we associate with the idea of the ‘disease of the year.’ The Kausi or S.W. monsoon still blows, but in this second or post-pluvial phase its strength is diminished. As on the western coast the mornings are misty, the effect of condensation and of excessive evaporation, the sun pumping up vapour from the rapidly desiccating ground; but about four hours after sunrise a strong sea-breeze sets in, giving a little life and elasticity to the exhausted frame. When the ‘doctor’ fails the heat is oppressive, and the sunsets are often accompanied by an unpleasant closeness. The beginning of the Kipupwe is held to be universally sickly. The Hindus, who declare that all cold coming from the south is bad, suffer from attacks of rheumatism and pneumonia. The charms of the season induce Europeans to despise the insidious attacks of malaria: they commit imprudences and pay for them in severe fevers. The rare but heavy showers that now fall are termed ‘Mcho;’ they separate the greater from the lesser Msika.