SOUNDINGS TAKEN DURING THE DISCOVERY INVESTIGATIONS, 1932-1939 43 



sounding report, and particulars appear also in the report on the R.R.S. 'Discovery II' by Ardley 

 and Mackintosh (1936, pp. 102-4). Though little used in recent years, the Lucas and Kelvin sounding 

 machines remained as part of our standard sounding equipment ; some amplification, however, of the 

 description of the echo-sounding sets given in the latter report is required, and details will be found 

 here in Appendix I (p. 95). 



DEEP-WATER ECHO-SOUNDING SET 

 During the six years in which the 'Acadia' type recorder was used with the deep-water echo- 

 sounding set, little electrical or mechanical trouble was experienced with the recorder mechanism, and 

 records covering some 900 hours of running were made and stored. Very approximately this represents 

 a continuous survey of about 6000 miles of the ocean floor, from which a virtually permanent record is 

 available, but the recorder was used also on numerous occasions for short periods up to 20 minutes from 

 which the record itself was not kept, but from which soundings had been noted. The positions ot the 

 great majority of these oceanic records are shown in Text-figs, i and 2. A large proportion of the stored 

 records were taken during the running surveys of the South Shetland and South Orkney Islands and 

 the tracks of the ship at these times are shown in detail in Text-figs. 3 and 4 together with the tracks 

 of records taken at Tristan da Cunha, South Georgia, the Balleny group and other islands. A consider- 

 able number of continuous records were also obtained in open water and across such features as the 

 Burdwood Bank, the Kerguelen-Gaussberg Ridge and a newly discovered bank in 42° S, on the meridian 

 of Greenwich. The depths recorded varied from 25 fm. (46 m.), the average minimum depth at which 

 soundings could be read,i to just over 3000 fm. (5486 m.), which was the greatest depth at which we 

 obtained a clear record. A complete list of all records, with their positions, is given in Appendix II (p. 98) 

 to this report. In Appendix I (p. 95), which deals mainly with certain technical difficulties met with in 

 the operation of the echo-sounding sets, reference will also be found to the effect of extraneous noises 

 on the echo marking on these records. Water noises and the passage of the ship through pack-ice can 

 completely obscure the echo marking, but on the whole our records are very free from interference 

 from these sources. 



SHALLOW-WATER ECHO-SOUNDING SET 



The sonic pattern 'listening' set, described in our previous reports, was in use until 1935, and was 

 then replaced by an Admiralty System Magnetostriction set with a Mark XII D recorder. This is 

 a supersonic set (emitting soundwaves beyond the audible range) and it was manufactured and fitted 

 by Messrs Henry Hughes & Son Ltd. The principle of the British Admiralty system of supersonic 

 echo sounding with magnetostriction transmission is well known and has already been described in 

 considerable detail in the Hydrographic Review (1934, 1936 and 1937). It is sufficient, therefore, to 

 say that the range of this new set was 0-130 fm. (0-238 m.) on the slow or normal speed, with one 

 phase addition of 100 fm., making the total range 0-230 fm. (0-421 m.). On the fast speed soundings 

 were obtained in feet, with a corresponding range of 0-230 ft. (0-70 m.). 



Few difficulties arose in the operation of this set, but there are certain technical points on which 

 fuller information appears desirable. This information, together with the details of the arrangement 

 of the transmitter and receiver in the hull of the ' Discovery II ', will be found in Appendix I (p. 95). 



1 At depths less than 25 fm. (46 m.) the echo marking on the 'Acadia' record tended to merge with the transmission 

 band. Reduction of the sensitivity of the receiving circuit allowed the echo marking to be clearly distinguishable at lesser 

 depths but, to allow for greater accuracy in the shallower soundings, it was our normal practice to use the shallow machines 

 for soundings less than 50 fm. {91 m.). 



