•JO CHALLENGER 



a month or so later, and then went to Trinidad for oil fuel prior 

 to returning to England. At the last minute a survey was ordered 

 in Dominica, off a small village called Portsmouth at the north- 

 westward end of the island. Commander Alun Jones enjoyed 

 sending his final departure signal to the Commander-in-Chief 

 West Indies Station — ' Challenger left Portsmouth for Portsmouth, ' 

 it read. But no word came from the C.-in-C. to indicate whether 

 he appreciated the coincidence or put it down to a signalman's 

 error. 



Outward bound again after the lie-up in May, 1936, the usual 

 water sampling and temperature observations were carried out 

 in the Atlantic. The programme of surveys for this season was 

 an extensive one in the vicinity of Trinidad. The island of Trini- 

 dad lies to the eastward of the coast of Venezuela, enclosing by 

 two long arms running to the west a great shallow area between 

 the island and the mainland. This is the Gulf of Paria, where the 

 depths of water vary from 8 to i ^ fathoms and below which a num- 

 ber of oil companies were at this time prospecting with a view 

 to drilling beneath the sea for oil. 



Challenger still had on the bridge the type of echo sounding 

 machine with which the operator listens for the returning echo. 

 The shallow floor of the Gulf of Paria is composed of soft, grey 

 mud, which made the returning echo impossible to hear. How- 

 ever, the new boat's set which had now been fitted recorded the 

 soundings on iodised paper in a similar manner to the deep water 

 set carried in the ship. In the boat set the small returning echo 

 was amplified on receipt from the sea-bed before the paper was 

 marked. So it was decided that the new boat's set must be in- 

 stalled in the ship to get the best results when ship sounding over 

 this soft, shallow bottom. The transmitter and the receiver of 

 this set, which can be imagined as the speaker and receiver of a 

 telephone, are fitted inside the hull of the boat in tanks which 

 are filled with fresh water. When the set was moved into the 

 ship these tanks posed a problem, until Lieutenant Menzies, the 

 Navigating Officer, thought of using upturned buckets welded to 

 the ship's hull which housed the transmitter and receiver 

 excellently. 



This echo set worked well and the survey went on apace. 



