EXPEDITION TOWARD THE NORTH POLE. 369 



therefore, to take altitudes when tlie sun is near the ijieridiau, as in- 

 dicated by the compass, with regard to the variations of the compass, 

 as derived from an isogonic chart. The time wheu the observation is 

 taken will, of course, be noted by the chronometer. Altitudes should 

 be taken in this way, both to the south and north of the zenith ; they 

 will enable the traveler to obtain his latitude at once very nearly, with- 

 out the more laborious computation of the time. 



The observations for time should be taken as nearly as may be when 

 the sun is at right angles to the meridian, to the east and west, the 

 compass being again used to ascertain the proper direction. This 

 method of proceeding will call for observations of altitude at or near 

 the four cardinal points, or nearly six hours apart in time. 



Wheu the party changes its place in the interval between their ob- 

 servations, it is necessary to have some estimate of the distance and 

 direction traveled. The ultimate mapping of the route will mainly 

 depend upon the astronomical observations, but no i^ains should be 

 spared to make a record every hour of the estimated distance traveletl — 

 by log, if afloat — of the direction of the route, b}- compass, and of bear- 

 ings of distant objects, such as peaks, or marked headlands, by which 

 the route may be plotted. 



In case of a few days' halt being made when a very high latitude has 

 been reached, or at any time during" the summer's explorations, a 

 special object of care should be to ascertain the actual rate of the 

 chronometers with the party. To this end, a well-defined, fixed object, 

 in any direction, should be selected as a mark, the theodolite pointed 

 on it, and the transit of the sun over its vertical observed on every day 

 during the sojourn at the place. If the party be only i)rovided with a 

 sextant, then the same angular distances of the sun from a fixed object 

 should be observed on successive days, the angles being chosen so as 

 to be between 30° and 45°. For instance, set the sextant successively 

 to 40O, to 40° 20', 40° 40', &c., and note the time when the sun's liml) 

 comes in contact with the object. The same distances will be found 

 after twenty-four hours, with a correction for change in the sun's declin- 

 ation. Tiie sun's altitude should be observed before and after these 

 observations, and its magnetic bearing' should be noted, as well as that 

 of the mark. The altitude of the mark should also be observed, if 

 practicable, either with the sextant or clinometer, but this is not 

 essential. J. E. Hilgaed. 



MAGNETISIM. 



Ou the voyage and sledge-journey, at all times when traveling, the 

 declination or variation of the compass should be obtained by observing 

 the magnetic bearing of the sun at least once every day on which the 

 sun is visible. On ship-board or in boats the azimuth compass is to be 

 used ; on land the small theodolite will be found preferable. 



Wheu afloat, no valuable observations of the maguetic dii) and in- 

 24 s 71 



