HYDROGRAPHICAL SURVEY. 185 



the cask. This lever, on the descent of the vessel, 

 being forced upward, lifted the valves, and allowed 

 a free course to the water, through the cask ; but, 

 on the motion downward being suspended, the valves 

 fell down by their weight, and prevented the water 

 from changing. It was generally allowed to remain 

 about half an hour at rest, that the wood might 

 attain the temperature of the sea in that situation, 

 and then hauled briskly up without stopping, and 

 the temperature of the contained water immediately 

 ascertained. In the ascent of the apparatus, the 

 lever connected with the upper valve, met the cur- 

 rent of water in a contrary way, pressed the valve 

 firmly down, and secured the water more effectually 

 within the vessel. 



The results thus obtained were highly satisfac- 

 tory ; the water brought up being invariably warmer 

 than that at vhe surface ; but, after a few experiments 

 had been made, the wood of the cask became soak- 

 ed with water ; several of the staves rent from end 

 to end ; and the apparatus became leaky and use- 

 less. 



Sir Joseph Banks, who manifested much interest 

 in these experiments, and favoured me with valua- 

 ble hints on the subject, from time to time, then 

 furnished me with an apparatus, made by Carey, 

 under the inspection of Messrs Cavendish and Gil- 

 pin, both of whom, it is remarkable, died before it 

 was completed. It was made chiefly of wood, and 

 bound with brass. But the first time it was sent 



