372 EXPEDITION TOWARD THE NORTH POLE. 



reuts iu the opeu polar sea, if such is found. No special observations 

 can be indicated, however, except those of the drift of icebergs, if any 

 should be seen. 



Density. — The dcnsiUj of the sea-water should be frequently observed 

 with delicate hydrometers, giving direct indications to the fourth deci- 

 mal. Whenever practicable, water should be brought up from different 

 depths, and its density tested. The specimens should be preserved in 

 carefully- sealed bottles, with a view to the subsequent determination of 

 their mineral contents. 



J. E. HiLGARD. 

 METEOROLOGY. 



The expedition is well supplied with meteorological instruments, all 

 the standards, with the exception of the mercurial barometers, manu- 

 factured by Casella, and compared with the standards of the Kew Ob- 

 servatory under the direction of Professor Balfour Stewart. Dr. Bes- 

 sels is so familiar with the use of instruments, and so well acquainted 

 with the principles of meteorology, that minute instructions are unne- 

 cessary. We shall therefore merely call attention, by way of remem- 

 brance, to the several points worthy of special notice.' 



Temperature. — The registers of the temperature, aa well as of the 

 barometer, direction of the wind, and moisture of the atmosphere should, 

 in all cases in which it is possible, be made hourly, and when that can- 

 not be done they should be made at intervals of two, three, four, or six 

 hours. The temperature of the water of the ocean, as well as of the 

 air, should be taken during the sailing of the vesseb 



The minimum temperature of the ice, while in winter quarters, should 

 be noted from time to time, perhaps at different depths; also that of the 

 water beneath. 



The temperature of the black-bulb thermometer in vacuo exposed to 

 the sun, and also that of the black bulb free to the air, should be fre- 

 quently observed while the sun is on the meridian, and at given alti- 

 tudes in the forenoon and afternoon, and these observations compared 

 with those of the ordinary thermometer in the shade. 



Experiments should also be made with a thermometer in the focus of 

 the silvered mirror, the face of which is directed to* the sky. For this 

 purpose the ordinary black-bulb thermometer may be 'used as well as 

 the naked-bulb thermometer. The thermometer thus placed will gen- 

 erally indicate a lower temperature than one freely exi)osed to radiation 

 from the ground and terrestrial objects, and in case of isolated clouds 

 will probably serve to indicate those which are colder and perhaps 

 higher. 



Comparison may also be made between the temperature at different 

 distances above the earth, by suspending thermometers on a spar at 

 different heights. 



The temperatuiG of deep soundings should "be taken with the ther- 



