^ ' MAEIOX ' ' EXPEDITION TO DAVIS STRAIT AND BAFFIX BAY 57 



Had there been no cloiuly weather nor unusual refraction, the 

 positions at sea wouhl have been very good, as such positions go. 

 Unfortunately, there Avere frequent periods when bad weather made 

 the heavenly bodies invisible and a feAV other periods when abnor- 

 mal refraction was suspected. The accuracy of the track positions 

 in some places at sea is, therefore, doubtful, though, in view of the 

 paucity of previous soundings, almost never to a seriously damaging 

 degree. Throughout all periods when sights were possible, many of 

 them would be taken, permitting good estinnites and interpolations 

 to be made for the dead-reckoning positions which had to be relied 

 on between the fixes — that is, during the bad Aveather periods. 



The ship's track Avas ahvays determined graphically by laying 

 doAvn and running forAA^ard the A^arious bearing and Sumner lines 

 on large-scale plotting charts that Avere on the Mercator projection. 

 The regular plotting sheets published by the Hydrographic Office of 

 the United States XaAy Avere used south of latitude 61° X. Special 

 charts constructed on board on a scale of 2.75 inches to the degree 

 of longitude Avere used for tracking farther north, as no regular 

 plotting sheets could be purchased prior to the departure of the 

 expedition for latitudes aboA^e the sixty-first parallel. 



The observations Avere Avorked out principally by means of Hydro- 

 graphic Office Publications 203 and 204 Avhen south of the latitude 

 60° 30' X., and by means of the liaA^ersine-cosine formula giA'en in the 

 American Practical Xavigator aaIicu farther north. Meridian and 

 ex-meridian siglits Avere Avorked out during the entire cruise by 

 means of the methods giA^en in the latter publication. 



At least 10 sun sights were Avorked out on each clear to partW 

 cloudy day. On daA^s that Avere mostly overcast almost as many sun 

 sights would usually be Avorked out, for, due to the desire to keep 

 track of the position accurately, the intervals between observations 

 AAere regularly shortened whencA^er the sun appeared to be in danger 

 of being obscured for a long period by clouds. 



The positions AA'ere carefully determined and checked and are be- 

 lieved to be free from any gross errors. Considering the number of 

 siglits and bearings taken and the methods of naA'igation used, they 

 are probably the best results that could haA'e been obtained. 



In general, the positions of the soundings taken off the coast can 

 be considered as reliable to fairly reliable, possible exceptions being 

 off Baffin and Resolution Islands, AAdiere unusual refraction may have 

 prevailed. On the Marion we seldom had positive evidence of un- 

 usual refraction, such as great distortion of objects near the horizon 

 and failure of sights taken at close intervals to agree Avell Avith one 

 another. It is thought that the references in the sailing directions 

 about the unusual refraction to be expected in the Davis Strait region 

 can be attributed in many cases to the land's being incorrectly plotted 

 on the existing charts. 



CORRECTIOXS APPLIED TO THE ECHO SOUNDINGS 



It is AA'ell knoAA'ii that echo soundings are not accurate as taken. 

 They have to be corrected for instrumental and personal errors; also 

 for errors arising from the varying speed of sound in the Avater 

 column under the ship. The fathometer on the Marion Avas con- 



6816.5—32 .5 



