INSTRUCTIONS. 17 



tend to the improvement of Geography and 

 Navigation, and the advancement of science in 

 general. In addition to those objects of pro- 

 minent interest which may be expected to pre- 

 sent themselves at the Pole, should you be so 

 fortunate as to reach that point, and which 

 you are also to attend to on every part of 

 your voyage, you are likewise to keep a correct 

 register of the temperature of the air, in various 

 situations, and at different depths; you will 

 cause the dip of the horizon to be frequently 

 observed by the dip sector, invented by Doctor 

 Wollaston, and ascertain what effect may be 

 produced by measuring that dip across fields of 

 ice, as compared with its measurement across 

 the surface of the open sea; you will also 

 cause frequent observations to be made for 

 ascertaining the refraction, and what effect may 

 be produced by observing an object, either 

 celestial or terrestrial, over a field of ice, as 

 compared with objects observed over a surface 

 of water; together with such other meteorolo- 

 gical remarks as you may have opportunities of 

 making. You are to attend particularly to the 

 height, direction, and strength? of the tides, and 

 to the set and velocity of the currents ; the 

 'depths and soundings of the sea, and the na- 

 ture of the bottom ; for which purpose you are 



c 



