1884.] Mr. Gamble, Meteorological Notes. 11 



Society to engrave these as in a few years time more accurate ones can 

 Jbe drawn. 



The Colonial observations are those given in the reports of the 

 Meteorological Commission, except in the case of G-raham's Town, 

 where a series of five years' observations, carefully taken some 

 years ago by the Boyal Engineers, was preferred. The Maritzburg 

 observations have been published by Dr. E. Mann, and th se at 

 Durban, Natal, are from sheets printed in Natal. 



Mean temperature is roughly speaking about one degree less than 

 the half sum of the maximum and minimum. Until we can get hourly 

 readings from some up-country station, perhaps this is the most trust- 

 worthy way of getting mean temperature that is available. 



The periods are not simultaneous ; had only simultaneous registers 

 been chosen, some very valuable registers would have been omitted, for 

 example, that kept at Worcester by Mr. Hugo, now C.C. of Aliwal 

 North, for the ten years 1862-1871. 



Of late years Stevenson cribs have been used everywhere, but 

 formerly there was no uniformity of exposure. The importance of 

 attending to exposure was well shown by Dr. Gill in a paper read 

 before the Eoyal Meteorological Society. At the Eoyal Observatory 

 one set of thermometers have for many years been kept in a window 

 crib, another set have recently been placed in a Stevenson screen. The 

 mean maximum in the window is more than three degrees lower than 

 the mean maximum in the Stevenson, while the minimum in the 

 window is nearly three degrees higher. 



With unpaid observers the maximum and minimum are convenient, 

 as there is no absolute need to read them exactly at the same hour 

 every day, and for most purposes of animal or vegetable life we wish 

 to know the extremes rather than the temperature at any fixed time. 



The maps and diagrams are very suggestive. For example, the 

 small mean monthly range (12*^) at coast places, the large range (often 

 over 30'^) at inland places. Dry places also like Clanwilliam and 

 Nel's Poort have hot days and cool nights. Simon's Town, Mossel 

 Bay, Port Elizabeth, East London, and Durban have all compara- 

 tively warm nights. This is partly due to the blanket-action of watery- 

 vapour preventing the radiation of dark heat from the earth, partly 

 to the Mozambique or L'Agulhas current, the temperature of the sea 

 being never less than 70^ oR Durban and over 76° in summer. 



It will be seen that the summer afternoons at Maritzburg are not so 

 hot as in our Western and inland districts ; and Mossel Bay, Port 

 Elizabeth, and East London have cooler summer afternoons than 

 Wynberg or Cape Town, the reason being that in the extreme West 

 the oummer is the dry time, while in the East summer is rainy, and along 

 the south coast there is some rain at all seasons. 



The coldness of the winter nights up-country is mainly due to the 

 considerable height above sea-level — radiation into space going on 

 unchecked. 



It is well known that the maximum always reads less on a mountain 

 than on the plain below, but this is not the case with the minimum. 

 The night temperature is sometimes colder on the plain than on the 

 mountain, as has been found in comparing the readings taken on Table 

 Mountain with those taken at the Eoyal Observatory. 



