96 DISCOVERY REPORTS 



i.e. ever}- 2| sec. The returning echo was detected by a carbon-granule hydrophone, ampUfied, 

 rectified and recorded on sensitized paper traversed by a stylus pen driven by the transmitter switch. 

 The paper, which was supplied dry, had been sensitized during manufacture with a solution of starch 

 and potassium iodide and, in the 'Acadia' pattern recorder, was wetted for use by passage over 

 a wick which was fed from a tank behind the paper. When the stylus was traversing the paper and an 

 echo or signal was received, the current at that moment passing through the stylus electrolysed the 

 starch-potassium iodide solution in the wet paper and the iodine thus set free made a stain which 

 commenced at the precise moment when the echo was received. As the paper travelled only at 

 approximately 1 1 in. per hour past the stylus, the spacing of the returning echoes was so close that 

 an almost continuous echo line was produced. In bad weather it was sometimes difficult to distinguish 

 the echo mark from the other marks caused by extraneous noises in the hydrophone, especially in 

 depths of more than 500 fm. (914 m.). Passage of the ship through brash ice, or pack-ice, had a similar 

 eflFect (see PI. XXX, fig. i). It was possible to adjust the strength of the echo current by increasing 

 or decreasing the sensitivity of the amplifier, but this had the disadvantage of having a similar effect 

 on the strength of the water noises set up in the hydrophone. Therefore, in rough weather, it was often 

 necessary to plug in the headphones to the telephone circuit and listen for the returning echo, marking 

 it on the record, if necessary, with the electric pencil provided. Difficulty was also met when the 

 returning echo coincided with an outgoing transmission, since the band, or mark, set up on the record 

 by the transmission was of such intensity that an echo might be blanked out for a distance representing 

 some 20 or 30 fm. on the record. A switch, however, was provided whereby it was possible to cut 

 out any required number of transmissions without interference to the receiving circuit, and by careful 

 manipulation of this switch it was possible to trace the line of the echoes through the transmission 

 band. A typical example may be seen in PI. XXXI, fig. i. Without the use of the switch this trans- 

 mission band would have completely obscured the echo at a depth of 1000 fm. (1829 m.). This cut-out 

 switch was also used in determining the correct phase for soundings in waters of unknown depth. 

 It will be appreciated that since the phase switch or dial was graduated only from o to 1000 fm., and 

 that since a transmission was made automatically each time the phase switch arm passed zero, then 

 an echo which appeared on the paper at a scale reading of, say, 200 fm., might equally represent 

 200, 1200, 2200, etc. fm. The correct phase, however, could easily be determined by cutting out all 

 transmissions after the first, listening on the telephone circuit, and watching the number of times 

 the phase switch arm had rotated before the echo was heard. 



The recorder mechanism was driven by a governed electric motor, the speed of which required 

 checking and adjustment as the set warmed up. A careful check with an accurate stopwatch was 

 made therefore during long runs and the rate noted at intervals for the subsequent correction of the 

 soundmgs. A note also was required, on the actual record, of any correction to the timing. If, for 

 example, the motor ran fast by, say, 1% for 600 min. (which was quite a common period during 

 survey work) the minute markings automatically recorded on the paper would at the end of the run 

 be 6 mm. ahead of the correct time and all the soundings recorded would be 1% too deep. This error 

 m depth was negligible in soundings less than 100 fm. (183 m.) but, as we were usually approaching an 

 unknown or imperfectly surveyed anchorage at the end of such a run, it was imperative for the 

 subsequent plotting of the soundings that the correct time should be known for each depth plotted. 

 Eventually it was found that nearly correct running ensued if the case containing the mechanism was 

 left open ; such mmor corrections of speed as were then necessary could be applied by means of a 

 sliding resistance which we fitted in addition in the ordinary governor circuit. 



Throughout the whole period in which the recorder was in use, few repairs were needed apart from 

 small mechanical and electrical adjustments. On one occasion there was a complete breakdown in 



