210 INTERESTING SCIENTIFIC WORK IN THE ARCTIC 



from Washington to Boston, no heavy instruments could be car- 

 ried, and especially so in the final dash like that accomplished 

 by only Cook and two Eskimos. The ordinary navigator's sex- 

 tant would be too heavy and bulky, and would have to be re- 

 placed by a less cumbersome instrument. Peary ordinarily car- 

 ried a small sextant, a so-called pocket sextant. The ship's 

 chronometer in its square case would give way to a good pocket 

 timepiece, though two or three small chronometers might be 

 carried. 



"The sea captain observes the altitude of the sun by bringing 

 it in contact with the horizon where sea and sky meet. But in 



the frozen north there is no such 

 horizon, the ice floes are thrown 

 up into hummocks and hills, and 

 an altitude of the sun above the 

 visible horizon would lead to in- 

 accurate results. On land ex- 

 ploration, an artificial horizon is 

 made by pouring mercury into 

 a little shallow tray. But mer- 

 cury freezes at 40 degrees below 

 zero. A blackened glass plate 



made horizontal by means of spirit levels was used by Cook and well 

 answered the purpose. 



'Tn a polar dash, the latitude is the important information 

 desired. Longitude, i. e., the difference between local and Green^ 

 wich time, is difficult to obtain and inaccurate. Consequently, 

 latitude must be determined by methods which will not involve 

 an accurate knowledge of the time. The sun's greatest altitude 

 during the twenty-four hours would give the time of local noon, 

 and latitude from such an observation could be readily deter- 

 mined; and twelve hours later at midnight the sun's altitude 

 would be least, and latitude could again be determined. When the 



POCKET SEXTANT. 



Instrument "by Queen & Co., 

 Philadelphia. 



