212 DISCOVERY REPORTS 



This air gives up moisture on its sudden expansion in the cold hammer chamber causing a sticky 

 emulsion to form with the oil used for lubricating the piston. The piston then sticks and it is necessary 

 to take off the head of the hammer to remove the piston for cleaning at very frequent intervals. 

 Eventually, while the ship was in cold waters, the hammer was run practically without lubricant, the 

 piston being occasionally wiped with a rag which had been soaked in very thin oil. Even under these 

 conditions it was still necessary to remove the piston for cleaning every 8 to 12 hours when the 

 machine was in constant use. During the refit in London in 193 1 the hammer was surrounded by a 

 steam coil which has had the desired effect of preventing the condensation of the water from the 

 compressed air. Another matter which required the frequent attention of the engineers was the air 

 compressor itself, which was found to be inadequate for the long periods of continuous running 

 demanded from it by the sounding programme. It was only by careful and continuous attention that 

 the motor and bearings were prevented from wearing out completely, and as the ability of a compres- 

 sor to run continuously for several days is a very important factor in our sounding work, a new 

 compressor, with a much larger capacity and of heavier construction, was fitted in London in 193 1. 

 Trouble was also experienced with the reducing valve for regulating the pressure of air required to 

 reset the hammer, but a new valve constructed on board overcame this difficulty. 



From 1926 to 1929, when only Lucas sounding machines were being used in oceanic 

 waters, soundings were usually taken when the 'Discovery' or the 'William Scoresby' 

 was stopped for observations on hydrology and plankton. In the ' Discovery II ' with an 

 efficient deep-water echo-sounding machine it was possible to take soundings at much 

 more frequent intervals, and on a number of occasions the machine was used day and 

 night without intermission for weeks at a time. For station work the Lucas machine was 

 superseded mainly on account of the great saving of time. A Lucas sounding to 5000 m., 

 which is roughly the average depth of our oceanic stations, takes at least li hours to 

 complete. The ship requires to be constantly manoeuvred with regard to this one wire, 

 and as the forward hydrological machine on the forecastle head of the ' Discovery II ' 

 is only 22 ft. aft of the Lucas sounding machine, it is impossible, except on very rare 

 occasions, to work deep water-bottles when the Lucas sounding wire is out. An echo 

 sounding on station does not take more than 5 min. to complete, and there is no hin- 

 drance to the deep water-bottles being lowered as soon as the ship is hove-to. In the 

 variable weather conditions which prevail in the Scotia Sea, where the majority of our 

 stations were worked, it was important to reduce the time taken for observations, and in 

 this respect great advantage was obtained from the use of the echo-sounding machines. 

 It is a testimony to their efficacy that at several hundred stations we relied wholly on 

 soundings obtained in this way, and that instruments were constantly lowered to within 

 a short distance of the bottom, even in the greatest depths, without ever coming in 

 contact with it. 



COMPARISON OF WIRE AND ECHO SOUNDINGS 



At various times, mainly during the early part of 1930, comparisons were made by the 

 ' Discovery 11', when weather conditions permitted, between Lucas and echo soundings. 

 The accompanying table gives the data obtained, the average of the 21 comparisons 

 showing a percentage excess of Lucas depth over echo depth of 1-42. The greatest and 

 least errors, in soundings of over 2000 m., were respectively 3-35 and 0-28 per cent. In 



