i i 



MAPJOX ' ' EXPEDITIOX TO DAVIS STRAIT AXD BAFFIN BAY 59 



The correction for each fathometer sounding as calculated was 

 applied right on the large chart rolls to the observed depth values. 

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

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

 comjDaring corrected red-light fathometer and simultaneously taken 

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

 index error of the aj^paratus. It does not vary with the depth or 

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

 fathometer oscillator and hj^lrophone being used below the water 

 line of the sounding ship. After the above tAvo corrections w^ere 

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

 far as possible. 



All the soundings in fact Avere noAv better than they w^ere w^hen 

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

 soundings Avhich it Avas possible, in large part, to eliminate. Fifty- 

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

 stations during the course of the expedition, and these Avere 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 w^ire soundings had been fair to good up-and-down 

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

 checks had rather consistent differences from the partly corrected 

 echo soundings Avhen the latter were grouped according to the watches 

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

 the fathometer readings. It was found that one officer, on the aA^er- 

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

 great, AAdiile 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 Avho 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 Avire soundings and the true depth. 



AVhen all offshore soundings had been corrected, the values obtained 

 in the harbors and inland Avaters 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 plotted 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 shoAvn on Figures 44 and 45. 



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

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

 different Avire 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 fcAv over plus or minus 50 fathoms in error, but this number 

 is undoubtedly A^ry small. 



FINAL RESULTS 



One of the last steps in Avorking 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 



