Prof. Bache’s Lecture on the Gulf Stream. 315 
depths. The substitution of a globe, for the cylinder, extended 
the range of these instruments, but the thermometers were often 
crushed or injured by the access of sea-water to the interior of 
the globe. Six’s self-registering thermometers as bearing con- 
_ Siderable pressure without injury and without rendering the in- 
- dications erroneous, and as requiring no case to enclose them, 
except to prevent breaking from accidental knocks in handling, 
are very useful. They are still favorites with many of the offi- 
cers, though others complain of their great liability to derange- 
ment, especially if the mercury is not perfectly clean, when the 
mercurial column easily separates and some skill is required to 
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