and other Countries in ancient times. 99 



and hence the mean of the whole year = 27°'4« C. Com- 

 paring this mean temperature with that of Cairo, in latitude 

 30°, the increase for five degrees of latitude is 1^° C, as 

 assumed before. 



Probably the number 27 0, 4 is rather too high, as the hours 

 of observation selected would lead to a result erring in excess. 

 But on the other hand it is to be remarked, that Darfur 

 comes within the limits of the tropical rains, which in this 

 part of Africa reach as far as 1 7° north, and tend to keep 

 down very much the heats of summer. In fact, Browne 

 never marks the thermometer above 38° *3 in Darfur, while 

 he mentions having observed 46°* 7 in the Great Oasis of 

 Egypt. It is in those portions of the torrid African zone, 

 where rain never or rarely falls, as in Upper Egypt, Nubia, 

 and Fezzan, that the heat of the day is most excessive. It is 

 true that the nocturnal radiation is also very great *, which 

 keeps down the mean temperature of the twenty-four hours ; 

 but during certain hours the vine would be probably exposed 

 to greater heat in the Egyptian Oasis than in Darfur itself. > 



III. Cultivation of the Vine in Britain. 



I think it is difficult not to feel very sceptical about any 

 extensive cultivation of the vine in ancient times in the 

 northernmost provinces of France, and in England. Strabo, 

 as M. Arago has remarked, indicates the line of the Cevennes 

 as the limit of the culture of the olive in France, which it still 

 is ; but the remainder of the sentence is, I think, equally re- 

 markable : 7] a/jL7re\o<; 8e irpolovaw ov pa$lco$ rekea^opel^, 

 "as one goes further into the country, the vine does not easily 

 bring its fruit to maturity." As to Britain, we are told ex- 

 pressly by Tacitus, the climate was not warm enough for the 

 vine %. 



The scanty notices of the climate of Great Britain to be 

 found in ancient authors agree remarkably with what we ex- 

 perience at the present day. Thus Caesar says, " Loca sunt 

 temperatiora quam in Gallia, remissioribus frigoribus." (Bell* 

 Gallic, lib. v. c. 12.) Thus Strabo : eiro/uiftpoL ftelalv oi aepe? 

 fjidWov r) vLfercbSecs, iv Se Tat? alQplais S/jlI^Xt) Kare^eu iroXvv 



* Caillaud speaks of water freezing at night on his journey between 

 the Great and Little Oasis : at 7 a.m. the thermometer stood at + 2°, at 

 noon at 19°. Capt. Lyon (p. 256.) speaks of ice half an inch in thickness 

 in the plains of Fezzan, south of Mourzouk. After these examples, it is 

 difficult to understand why the thin cake of ice observed by Oudney and 

 Clapperton on their road from Bournou to Sockatoo should have excited 

 so much surprise. 



f Strab. iv, 1. J Agricola, c. 12. 



H2 



