FIRST VOYAGE OF CAPTAIN ROSS. 
75 
the variation and inclination of the magnetic needle, and the 
intensity of the magnetic force, you will endeavour to ascertain 
how far the needle may be affected by the atmospherical elec¬ 
tricity, and what effect may be produced on the electrometer and 
magnetic needle, on the appearance of the Aurora Borealis, 
You will keep a correct register of the temperature of the air, 
and of the surface of the sea, and you will frequently try the 
temperature of the sea in various situations and at different depths. 
You will cause the dip of the horizon to be frequently observed 
by the dipsector, invented by Dr. Wollaston, and ascertain what 
effect may be produced, by measuring that dip across fields of 
ice, as compared with its measurement across the open sea. 
You will also cause frequent observations to be made for ascer¬ 
taining the refraction; and what effect may be produced by ob¬ 
serving 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 meteorological 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 current; the depths and soundings of the sea, and 
the nature of the bottom, for which purpose you are supplied with 
an instrument, better calculated to bring up substances than the 
lead usually employed for this purpose. 
For the purpose not only of ascertaining the set of the currents 
in the arctic seas, but also of affording more frequent chances of 
hearing of your progress, we desire that you do frequently, after 
you shall have passed the latitude of 65° north, and once every 
day, when you shall be in an ascertained current, throw over¬ 
board a bottle, closely sealed, and containing a paper stating the 
date and position it was launched, and you will give similar 
orders to the commander of the Alexander, to be executed in 
case of separation. And for this purpose we have caused each 
ship to be supplied with papers, on which is printed in several 
languages a request, that whoever may find it should take mea¬ 
sures for transmitting it to this office. 
And although you are not to be drawn aside from the main 
object of the service on which you are employed, as long as 
you may be enabled to make any progress, yet whenever yo} 
