STEPPES AND DESERTS. 



27and 32Eeaumur (93and 104Fahrenheit),and generally 

 not higher, providing the observation be made in the shade, 

 at a distance from all solid bodies which could radiate heat 

 to the thermometer, not in an air filled with hot particles 

 of dust or sand, and not with spirit thermometers, which 

 absorb the light. It is probably to fine grains of sand 

 floating in the air, and forming centres of radiant heat, that 

 we must ascribe the dreadful temperature of 40 to 44.8 

 Eeaumur (122 to 133 Pah.) in the shade, to which my 

 unhappy friend Eitchie, who perished there, and Captain 

 Lyon, were exposed for weeks in the Oasis of Mourzouk. 

 The most remarkable instance of very high temperature, 

 in an air probably free from dust, has been recorded by an 

 observer who knew well how to place and to correct all his 

 instruments with the greatest degree of accuracy. Eiippell 

 found 37.6 Eeaumur, (110.6 Fahrenheit,) at Ambukol in 

 Abyssinia, with a clouded sky, strong south-west wind, and 

 an approaching thunderstorm. The mean annual tempera- 

 ture of the tropics, or of the proper climate of palms, is, on 

 land, between 20.5 and 23.8 Eeaumur (or 78.2 and 

 8 5. 5 Fahrenheit) without any considerable difference 

 between the observations collected in Senegal, Pondi- 

 chery, and Surinam. (Humboldt, Memoire sur les lignes 

 isotherm es, 1817, p. 54. - Asie Centrale, T. iii. Mahlmann, 

 Table iv.) 



1 The great coolness, I might almost say cold, which prevails 

 for a considerable part of the year within the tropics on the 

 coast of Peru, causing the thermometer to sink to 12 

 Eeaumur (59 Fahrenheit), is, as I have noticed elsewhere, 

 by no means to be ascribed to the vicinity of the snow- 



