1 24 On the Climate of the Canary Islands, 



kept north of the forty-fifth parallel. The observations o£ 

 Heberden, at Madeira, in 1750, which were the only ones exist- 

 ing in the intermediate parallels alluded to, could not be re- 

 garded as sufficiently satisfactory for this purpose. The desi- 

 deratum has been at length supplied by a most careful register 

 kept at Santa Cruz, in TenerifFe, with good English instruments, 

 in an open gallery in the shade, from May 1808, to August 

 1810, by Don Francisco Escolar. The temperature of each 

 day is derived from the mean of two observations, one made 

 at sunrise, and the other at noon, or a little later. It might 

 appear, at first view, that, whilst the observation at sunrise may, 

 without hesitation, be admitted to have shown the minimum, — 

 that at noon, or a little later, might not justly represent the 

 maximum, — and, consequently, that the mean derived from 

 them would give a temperature somewhat too low ; and this view 

 might receive confirmation, on observing that the average tem- 

 perature of the noon register does not exceed that of sunrise by 

 more than 1°.16 R. or 2°.6 Fahr. But experience has shown 

 that, in the islands of warm climates, the maximum of heat very 

 rarely, indeed, happens so late in the day as halfpast one : that it 

 more frequently occurs a little after eleven, but most frequently 

 about noon. The increase of heat which takes place elsewhere 

 after the sun has reached the meridian, is, in such localities, 

 counteracted by the sea breeze, which, springing up when the 

 sun has reached a considerable altitude, increases in strength, 

 in proportion to the effect produced by the sun's increasing 

 heat upon the land. And in respect to any inference which 

 might be drawn from there being so small difference between, 

 sunrise and noon in Escolar's register, the observations of 

 Heberden, which contain the highest and lowest temperatures 

 experienced in every month in Madeira, show that, in no single 

 instance, the range of the thermometer for the space of a 

 whole month exceeds in that island 2°. 91 R., or 6°. 5 Fahr. 



From these considerations M. von Buch concludes that Don 

 Francisco Escolar's observations may be regarded as affording 

 a fair representation of the mean temperature at Santa Cruz, 

 The abstract of the register gives the following mean tempera-^ 

 tures for each month in the year ; — 



