' ' MARIOX ' ' EXPEDITION TO DAVIS STEAIT AND BAFFIN BAY 59 



The correction for each fathometer sounding as calculated was 

 api^lied right on the large chart rolls to the observed depth values. 

 In addition. 2 fathoms were taken from each fathometer value to 

 allow for the fathometer constant, a number which was obtained by 

 comj^aring corrected red-light fathometer and simultaneously taken 

 wire soundings Avith each other. The fathometer constant is a sort of 

 index error of the apparatus. It does not vary with the depth or 

 character of water column, but with the location of the particular 

 fathometer oscillator and hydrophone being used below the water 

 line of the sounding ship. After the above two corrections were 

 applied, the shallow water or red-light soundings were corrected so 

 far as possible. 



All the soundings in fact were now better than they were Avhen 

 first taken, but there still remained personal errors in the white-light 

 soundings which it was possible, in large part, to eliminate. Fifty- 

 three wire soundings, over 100 fathoms deep, had been taken at 

 stations during the course of the expedition, and these were now 

 analyzed in comparison with the partly corrected white light echo 

 soundings which had been taken simultaneously in the same places. 

 Some 35 of these wire soundings had been fair to good up-and-down 

 casts taken during moderate weather. It was seen that these reliable 

 checks had rather consistent differences from the partly corrected 

 echo soundings when the latter were grouped according to the watches 

 of the different officers who had had the deck and taken and recorded 

 the fathometer readings. It was found that one officer, on the aver- 

 age, had recorded all of his white-light soundings 32 fathoms too 

 great, while the three others had recorded them, on the average, only 

 11 fathoms too great; 32 or 11 fathoms, therefore, were taken from 

 all the partly corrected white-light soundings plotted on the chart, 

 depending upon who had had the watch during which they were 

 taken. This completed the corrections to all of the offshore sound- 

 ings, and brought them, on the average, as close as possible to the 

 good w^ire soundings and the true depth. 



When all offshore soundings had been corrected, the values obtained 

 in the harbors and inland waters were corrected in the same general 

 manner. These were plotted on special large scale charts of the 

 areas concerned, the soundings being much too close together in these 

 regions to permit their being ):)lotted and corrected on the chart rolls 

 containing the offshore soundings on the scale of 4 inches to the 

 degree of longitude. Some of the corrected soundings obtained in 

 inland waters are shown on Figures 44 and 45. 



It is hard to say how much the fully corrected fathometer values 

 may vary from the true depth, just as it is to say how far wrong the 

 different wire soundings may be. It is thought that the completely 

 adjusted fathometer values are correct in at least half of the cases 

 to within plus or minus 25 fathoms for all depths. There are prob- 

 ably a few over plus or minus 50 fathoms in error, but this number 

 is undoubtedly very small. 



FINAL RESULTS 



One of the last steps in working up the soundings data was to 

 construct a general chart of the Davis Strait region on the polyconic 

 projection on the scale of 30.000 meters to the inch. To this" chart 



