from shore outward by means of a glass bottomed boat and window buckets . 

 With an overhead sun, it was possible to follow the cable to depths of 

 sixty or seventy feet. It lay in a straight line except for some slack 

 at the splice box and was covered by sand in a few places. At about 

 seventy feet, the depth began to increase markedly and the bottom and 

 cable was lost from view before the shallow hydrophone was reached. 

 Later, it was found in a large clear patch of white sand at a depth of 

 100 feet by scuba divers. The hydrophone was covered with a layer of 

 sand and left in place. The bottom, from shore to hydrophone, consists 

 of clear white sand with occasional patches of greenish=brown marine 

 growth and flat outcroppings of limestone. 



(c) Position Determination 



As the R/V LORD KELVIN payed out cable, her range and true 

 bearing from a midpoint on the shore line of the Lerner Laboratory pro- 

 perty was obtained with a range finder and pelorus. The observations, 

 read at intervals of two or three minutes , were radioed to the boat 

 and tabulated with depth as read from a direct reading fathometer. 



The pelorus consisted of a circular scale and pointer attached 

 to the range finder from which the angular setting could be read. North 

 was determined by setting the range finder on the North Star. The range 

 finder, a split field type, was one meter in length. For distances up 

 to two miles, range could be read to within 300 feet and bearing to 

 within one degree. 



Position was also obtained aboard the R/V LORD KELVIN, from 

 sextant readings of the angles between Entrance Point and the Lerner 

 Laboratory and between the Lerner Laboratory and Paradise Point. 



The path of the cable ship and hydrophone positions obtained 

 with the two methods are shown in Figure 14. The observations are in 

 good agreement up to the position of hydrophone A, The differences in 

 the observations beyond are larger than one would expect and a satisfactory 

 explanation for them has not been found. 



Recently, determinations of the hydrophone positions were made 

 from travel time measurements of sounds produced by blasting caps. The 

 caps were detonated from a vessel anchored at three different locations 

 along the 20 fathom contour. The vessel's locations were determined 

 with the range finder- pelorus method used earlier. The position obtained 

 for hydrophone B, Figure 14, differs considerably from the positions 

 obtained earlier and is believed to be more reliable than the earlier 

 observations. The location of hydrophone A was confirmed to within some 

 100 yards. 



It is planned to make further determinations of the hydrophone 

 positions with blasting caps. The location of the vessel from which the 

 caps are detonated will be obtained by range and bearing observations as 

 before but with better equipment. With care, it should be possible to 

 locate the hydrophones to within 100 feet. 



