brightness, a technique readily adaptable to a scientist 

 using the bathyscaph. Distance to the emanating source 

 can also be approximated. 



Clarke^ has, in view of the above problem, considered 

 the light intensity of a given flash of point source in relation 

 to its possible distance from a sensing instrument. His 

 experiments and deductions reveal, as a best estimate, 

 that the maximum possible sensing range of a photometer 

 is about 10 meters. His calculations and conclusions seem 

 correct, as 10 meters represents the maximum estimated 

 distance that such sources can be seen by the human eye 

 from within the bathyscaph. This assumes equal sensitivity 

 between instrumental sensors and the human eye. 



Virtually continuous observations to determine the 

 presence of bioluminescence throughout the large water 

 column have been made during ascents of the TRIESTE 

 (Dives Nos. 61, 76, 77, 78). Results are shown in table 2. 

 It appears that bioluminescent flashes are normal at great 

 depths and do not necessarily require tactile stimulation 

 by a source such as the moving bathyscaph. Although Dietz^ 

 reports that i^. is an advantage to have the eddy current 

 behind the bathyscaph, as during the ascent, because this 

 stimulates organisms to luminesce; subsequent observations 

 have revealed that this contributes only modestly to the 

 flashing rate. A burble or knuckle of water does follow 

 behind the bathyscaph on the ascent and this usually does 

 elicit a small increase in the the amount of biolumines- 

 cence. As the maximum ascent rate of the TRIESTE is 

 never more than 2 meters per second, the water current 

 activity behind the bathyscaph is relatively slight. 



The quantity of bioluminescence remained substantially 

 the same for conditions of descent and ascent. Exceptions 

 noted were the breakup of strings of point flashes and en- 

 tanglement of medusae in the external rigging of the 

 TRIESTE during ascent. It is well known that tactile 

 stimulation will elicit significant increases of biolumines- 

 cence in surface "burning water. " (However, dropping of 

 ballast, which should be a potent tactile stimulus in a 

 limited area, resulted in little bioluminescence. ) 



By analogy, the concentration of bioluminescence at 

 any one time rarely exceeds the number of stars that can 

 be seen in the heavens on a clear, dark night. Evidence 

 of virtually incessant flashing in the viewing area was 

 observed by Piccard (personal communication) in 1956. 



35 



