THE CLIMATE OF LOUREN^O .MAKOUES. ^IJ 



month of March, which is characterised by an increase in the 

 velocity of the wind, the evaporation Hkewise increases. The 

 inflnence of pressure and humidity, which are factors of less 

 importance, is not contradicted by an examination of the respec- 

 tive daily ranges. 



Data are lacking for the study of evaporation during the dif- 

 ferent hours. Its extraordinary increase during the hours of 

 occurrence of the hot zvind has, however, become c|uite evident. 



Table No. XIII, showing the means of monthly evaporation, 

 will confirm the above remarks on the subject. 



Cloudiness and Hours of Sl'nsfiine. 



The state of cloudiness is of great imjjortance in nieteor- 

 ologv, because, apart from its close connection with ramfall. it 

 has a great influence in the distribution of solar radiation and ter- 

 restrial radiation, and alTords data for the study of the upper 

 currents of the atmosphere and for the forecasting of the weather. 

 Recent researches by Professor Abbot, tending to demon- 

 strate the influence of the clouds on the percentage of solar 

 racHation which reaches the terrestrial surface, lead him to con- 

 clude that the solar rays sufl:'er a loss of =io % in value when 

 passing through a cloudless atmosphere, and this percentage of 

 loss noticeably increases with cloudiness, through absorption and 

 reflection. 



Taking it that an average of 52 % of the terrestrial 

 surface is obscured by clouds, he concludes that the solar 

 radiation which reaches the terrestrial surface is reduced to 

 24 % of its total amount, and this fact enhances the influence of 

 cloudiness in Meteorology. 



Observations of cloudiness are made at the < )l)seryatory 

 three times a day, at IX, XV and XXI. 



The monthly average of the amount of chnul i> in agree- 

 ment with the distribution of rainfall. From the hours of 

 observation a decrease is recorded from morning towards night, 

 except in June and July, when the greatest amount of cloud is 

 legistered at XV. 



The number of ol)servations of clear sky and sky with a 

 smalll quantity of cloud exceeds those of overcast sky with or 

 withottt breaks. 



The average cloudiness of Lourenco Manjues (4.^)) closely 

 a]jproaches the figure attributed to this latitude in the cloudiness 

 charts, and nears the maximum cloudiness of South Africa. 



" Cumulus "' clouds prevail all the year round, and during the 

 rainy season " cumulus " and " cumulo-nimbus." " Cirrus " 

 are observed more esi)ecially in the afternoon, from January to 

 March, and in May, freciuently grouped from SW to Xk^ and 

 sometimes seeming to irradiate from a point in the SW ((uadrant : 

 they move more usually from W to E. " Stratus " are more 

 frequent in the morning of the cool season. 



