Oct. 1 6, i 



NA TURE 



589 



METEOROLOGY OF THE LOWER CONGO 1 

 TN this work Dr. Danckelman has made a valuable 

 ■l contribution to the meteorology of Africa. The 

 observations, which are printed in extenso, were made at 

 Vivi, lat. 5 35' S., long. 13° 52' E., at a height of 374 feet, 

 from May 1882 to August 1S83. The hours of observa- 

 tion were 7 a.m., 2 p.m., and 9 p.m., and to these were 

 added for the six months ending May 1S83 observations 

 at 6 a.m. and 8 a.m., which thus furnish important data 

 regarding the march of diurnal phenomena for the first 

 three hours after sunrise. The full details which are 

 given of the instruments employed, their exposure, and 

 the methods of observing are particularly satisfactory. 

 While the instrumental observations are very complete, 

 no less care has been taken to make the non-instrumental 

 observations of weather equally complete, and these have 

 been planned and carried out to aid in discussions affect- 

 ing both local and general meteorology. 



In resuming and discussing these sixteen months' 

 observations, Dr. Danckelman has conjoined with the 

 results obtained for Vivi the results of observations made 

 at St. Thomas, Gaboon, Chinchoxo, Loanda, and Melange, 

 these places roughly representing the west of Africa from 

 near the equator to about lat. io° S. At all these places 

 the annual minimum pressure occurs in February or 

 March and the maximum in July, with a small secondary 

 maximum in January. At Vivi atmospheric pressure at 

 32° and sea-level is 25^932 inches in February, 30T17 

 inches in July, and 29^997 inches for the year. 



At Vivi the mean annual temperature is 76°*4, the 

 lowest monthly mean being 7o°'5 in August, and the 

 highest 79 "5 in February. The highest observed tem- 

 perature was 97°'2 on November 5, 18S2, and the lowest 

 53°'S on July 29 of the same year. A noteworthy feature 

 of the climate of Vivi is the relatively low temperature 

 from June to September ; during the other eight months 

 the means vary only from 77°'4 to 79°'$. This feature is 

 common to the whole of this region of West Africa ; and 

 it corresponds to the dry season of the year, which, as 

 regards the Lower Congo, is characterised by Dr. 

 Danckelman as undoubtedly the most agreeable and the 

 finest, as well as the healthiest, season of the year. On 

 the other hand, on the elevated plateaux of the interior, 

 the heat is very great during the day, and many maladies 

 prevail among the natives, numbers of the ill-clad blacks 

 succumbing to the diseases caused by exposure to the 

 low temperature of the nights. The temperature of the 

 Congo was observed at intervals during the year, the 

 observations being made at a part of the river where the 

 current was rapid. The results give a mean annual tem- 

 perature of 8i°'S, being thus 5°*4 higher than that of 

 the air. 



Of the winds observed at Vivi the percentages are 

 south-west, 39 ; west, 15 ; west-south-west, 9 ; north, 8 ; 

 and calms, 18 ; winds from any other direction being of 

 rare occurrence. Thus of the 82 per cent, of wind-direc- 

 tions observed, 63 per cent were from the south-west 

 quadrant. During the whole year south-west winds pre- 

 dominate in the afternoon, but during the dry season the 

 wind frequently veers to west towards evening, so that at 

 9 p.m. west and west-south-west winds are more frequent 

 than south-west, whilst south and south-south-west winds 

 very rarely occur. This striking predominance of south- 

 westerly winds has important bearings on the climatology 

 of the whole of the Lower Congo as respects humidity, 

 cloud, and rainfall. A striking peculiarity of the climate 

 are the strong winds which often set in late in the after- 

 noon and evening, and which are carefully recorded in 

 the journal of the observations. The following are the 

 number of times such winds have occurred each hour 

 from 3 p.m. to 11 p.m.,— 6, 11, 24, 28, 30, 32, 22, and 4, 



1 " Memoire sur les Observations Meteorologiques faites a Vivi (Congo 

 Inferieure), et sur la Climatolo^ie de la Cote sud-onest d'Afrique en general." 

 Par Dr. A von Danckelman. (Berlin, 1884.) 



the hours of greatest frequency thus being from 5 p.m. to 

 10 p.m. During the other hours of the day they seldom 

 occur. The degree to which this prevails is seen from 

 the fact that the mean force of the wind is greater at 

 9 p.m. than at 2 p.m., the latter hour being the time about 

 which the wind generally attains its maximum diurnal 

 velocity over the land. 



Thunderstorms are of frequent occurrence from Novem- 

 ber to May but none were recorded from June to October. 

 As regards their distribution during the day, scarcely any 

 occurred from 1 1 p.m. to noon, the period of maximum 

 frequency being from I p.m. to 8 p.m. ; but particularly 

 from 4 p.m. to 6 p.m., 29 per cent, of the whole having 

 occurred during these two hours. During the rainy 

 season heat lightning is of frequent occurrence in the 

 south, east, and north horizon, but rarely in the west. 

 When the wind shifts from the ordinary south-west direc- 

 tion into east, the change is almost invariably followed 

 by a thunderstorm, or by thundery-looking clouds, which 

 indicate a thunderstorm not far off. Thunderstorms 

 most frequently advance from the east. During the 

 sixteen months the number of storms which advanced 

 from an easterly direction was fifty-three, whereas only 

 fourteen came from a westerly direction. The severest 

 thunderstorms come from the north-east. They are in- 

 timately connected with the rainfall, which being wholly 

 dependent on the thunderstorm, the diurnal periods of 

 the two phenomena are the same. The rainiest months 

 at Vivi were November, 11*34 inches; December, 8*94 

 inches ; April, 9'io inches ; and March, 5*67 inches. The 

 annual amount was 42^56 inches. No rain fell from June 

 to September, and the fall in October was very small. 

 During the dry season, however, when no rain falls, the 

 hygrometer not unfrequently indicates an atmosphere 

 highly charged with vapour, and occasionally a light 

 drizzle sets in which the Portuguese call " Cacimbo," but 

 the amount falling is too small to be measurable. These 

 results show, in an unmistakable manner, the powerful 

 and beneficial influence of the prevailing south-westerly 

 winds from the Atlantic on the climate of this extensive 

 region in the continent of Africa. 



THE RECENT ECLIPSE OF THE MOON 



\A/E have received the following communications with 

 * * reference to the recent lunar eclipse : — 



The total eclipse of the moon on Saturday, October 4, 

 was of particular importance as it was — since the one in 

 1877, which was practically lost through bad weather — 

 the first opportunity of measuring the changes which the 

 heat radiated by the moon undergoes with the proceeding 

 eclipse. And indeed on Saturday evening at six o'clock 

 it appeared highly probable that the fate of this eclipse 

 would be the same as that of its predecessor, the sky 

 being thickly covered with misty clouds, with hardly any 

 motion whatever. Suddenly, however, as if by magic, 

 thirty-two minutes before the beginning of the total phase, 

 they all disappeared, and left a most perfect and excep- 

 tional clearness behind them, which not only lasted during 

 the remainder of the eclipse, but also through the two fol- 

 lowing days and nights. Thus I was enabled to carry out 

 the greater part of my programme in every detail. The 

 apparatus used was the same which the Earl of Rosse 

 described in his communications to the Royal Society in 

 1869, 1870, and 1873 ; ^ condenses by means of two 

 small concave mirrors alternately on two thermopiles 

 the rays of the moon collected by the 3-foot telescope, and 

 the currents thus created are measured by the aid of a 

 galvanometer with mirror and scale. The time of ex- 

 posure was I min. sid. time for each pile, and the observa- 

 tions were throughout the eclipse carried on with only two 

 interruptions of eight and nine minutes, the former caused 

 by my examining the condensing mirrors for dew, the 



