314 THE CLi:\IATR OF LOURENQO MARQUES. 



and vapour tension is recorded at XXI, this l)eing no dotibt con- 

 nected with the aforesaid march of the variation of temperature. 



The march of vapour tension, both annual and daily, regu- 

 larl\- follows temperature. Mean annual vapour tension is 

 ]4.7r""\ and the mean variation oscillates between 3. 11 """ and 

 5.15'"'" in a similar but more regular manner than is the case 

 with temperature, and the same agreement exists in its dif- 

 ferences. The dittrnal minimum takes place at the hour of the 

 minimum temperature ; the maximum varies between XIII and 

 X\'I1, and is later than the maximum temperature, es])ecially in 

 the coolest months. 



The extreme ranges in 4 years are: Maximum Jh.^'""', 

 mininmni 4.3'"'". 



The foregoing emphasises to a considerable extent the high 

 condition of relative humidity during the night. 



Dew is very frequent from June to Sei)tember. The rain 

 gauge (2 decimetres in diameter) sometimes records o.T'"™, 

 0.2'"'", and very seldom 0.3'"'". 



Idle dew and fog water collectetl in the rain gauge in 191 2 

 amounted to i2.i'""\ It shotild be noted that the i>ercentage of 

 cloudiness last year was less than usual. 



It is generally acknowledged that the percentage of cloudi- 

 ness has a considerable influence upon dew. The smallest 

 amount of average cloudiness in Lourenco Marques is at XXI in 

 relation to the hours of observation. I shotdd, nevertheless, " 

 mention that Dr. Sutton, as a result of his direct observations at 

 Kimberley, concluded that a clear sky was not essential to the 

 formation of dew. that this merely contri1)utes to hasten its com- 

 mencement, an.d that the dampness of the air and the length of 

 the night are the determining factors in the formation of dew. 



1 often noticed that there was abundant dew in cloudy nights, 

 and this fact confirms Dr. Sutton's opinion. 



There is no dew with N and NNW winds, the former show- 

 ing a higher record during such nights when a gentle landbreeze 

 is l)lowing. 



Rainfall. 



The meteorological data of regions which, like Lourenco 

 Marciues, are situated within the zone limits, is more or less 

 afliected by the characteristics of the two zones with which they 

 connect. 



The rainv season in Lourenco Marques from October ta 

 ]March. nameiv, when the sun is nearer the zenith, corresponds 

 to the tropical condition {vertical sun). During the six months 

 from April to September, the quantity of water recorded by the 

 rain gauge is about one quarter of that falling during the rainy 

 season, a small increase being noticed in the month of July, 

 which, though insignificant, may perhaps have its origin in the 

 winter rainfalls, which are more comnx)n in sub-tropical climates. 



The annual rainfall mean is 677""" (26.660"), which 



