Hydrography, and the Art of' Navigation. 57 



the vicinity of the southern pole. The temperature of this cur- 

 rent was first noticed by M. de Humboldt, and it has been ex- 

 amined with very particular care during the voyage of the Co- 

 quille. The frequent observations on the temperature of the 

 ocean which the officers of the Bonite will not fail to make be- 

 tween Cape Horn and the equator, will serve to extend or com- 

 plete the important results obtained by their predecessors, espe- 

 cially by Captain Duperrey. 



Major Rennel has described, with minute attention, the cur- 

 rent which emanates from the south-east coast of Africa, and runs 

 along the south bank of Agullas. According to the observations 

 of Mr John Davy, the temperature of this current is from 4° to 

 5° Cent. (7° to 9° Fahr.) higher than that of the neighbouring seas. 

 This high temperature is more deserving of the attention of na- 

 vigators, from its being supposed to be the immediate cause of 

 the cloud of vapour called the Tahle-cloth, which always en- 

 velopes the summit of the Table Mountain, whenever the wind 

 blows from the south-east. 



Temperature of the Sea at great depths, — It is not to be ex- 

 pected that a vessel such as the Bonite, dispatched on a special 

 mission to the most distant quarter of the globe, will ever de- 

 lay its progress for the express purpose of engaging in physical 

 experiments. At the same time, when hours, and even entire 

 days of dead calm are to be expected, especially when it is ne- 

 cessary to cross the line frequently, we conceive that this expe- 

 dition will act wisely by providing thermometographical and 

 sounding apparatus, for the purpose of sinking instruments in 

 safety to the greatest depths of the ocean. There is now very 

 little doubt that the inferior cold waters of the equinoctial 

 regions are conveyed thither by submarine currents from the 

 polar zones ; but even the complete solution of this theoretical 

 point, will be far from depriving the observations we now re- 

 commend of their interest. Who does not see, for example, 

 that the depth at which the maximum of cold is found, and we 

 may even say such and such differences of temperature, must 

 depend, in every latitude, in a very direct manner, on the total 

 depth of the ocean ; so that we may expect that the latter may 



