| v i,i INTRODUCTION. 



this, I have thought, might be imputed in part the difference in the 

 preoBore. 



The intensity of light and feebleness of the solar radiation has hern 

 proved, by our instruments, to be much less in the southern hemi- 

 sphere in high latitudes: the former appears to be confirmed by the 

 c\l>eriments made to ascertain the penetrability of light in the water. 

 The experiments which have led to these results cannot be given in 

 tliis place. They belong to another part of this work, in which they 

 will be given in detail. On the temperature, it will be unnecessary 

 for me to say anything farther, as I have already made reference to 

 it, in the explanations of the diagrams and the remarks I have ofti-ivd 

 on the various climates we have visited. 



