186 ACCOUNT OF THE ARCTIC IlEGIONS. 



to the depth of 300 fathoms, the wood swelledj 

 opened, and became leaky, and two plate glass illu- 

 minators, intended^ to admit light for reading oft 

 the degrees on a Sia:''s thermometer, which accom- 

 panied it, were broken. Thus this apparatus was 

 also rendered useless. After this, I made a model 

 of a similar instrument, and got it cast in brass. 

 This I fitted np, with the assistance of an ingenious 

 mechanic, and applied to it the valves made by 

 Carey, which then proved an elegant and useful 

 apparatus. This instrument, which I called a ma- 

 rine divc?% is represented in plate 2. fig. 2. It waf 

 14 inches in length, 5 inches in diameter at the top, 

 and 6 at the bottom. The illuminators, consisting 

 of plate glass, were each 8 inches long, and 2 to 2^ 

 inches broad, and were placed on opposite sides. 

 The form of the instrument was an octagonal ta- 

 pering prism. A slender spring operated on a qua- 

 drant of brass, fixed to the hinge-part of each valve, 

 and was so adjusted, as merely to support the valve, 

 when placed in its most open position, but no more. 

 The top of the instrument was fixed on by two 

 thumb screws, and could be removed in a few se- 

 conds, for facilitating the examination of the water. 

 The weight of the whole being 23 pounds, it never 

 required any load for sinking it. 



With this instrument, and the fir-cask before 

 mentioned, I completed a series of experiments on 

 submarine temperature, as far as contained in the 

 following table. 



