THE PHYSICAL CONDITIONS OF THE ABYSS 25 



The more recent experiments that have been 

 made, tend to show that no sunlight whatever pene- 

 trates to a greater depth, to take an extreme limit, 

 than 500 fathoms. 



Fol and Sarasin, experimenting with very sensitive 

 bromo-gelatine plates, found that there was no reac- 

 tion after ten minutes' exposure at a depth of 400 

 metres on a sunny day in March. 



But although it is highly probable that not a 

 glimmer of sunlight ever penetrates to the depths 

 of the ocean, there is in some places, undoubtedly, a 

 very considerable illumination due to the phosphor- 

 escence of the inhabitants of the deep waters. 



All the Alcyonarians are, according to Moseley, 

 brilliantly phosphorescent when brought to the sur- 

 face. Many deep-sea fish possess phosphorescent 

 organs, and it is quite possible that many of the deep- 

 sea Protozoa, Tunicates, Jelly-fish, and Crustacea are 

 in their native haunts capable of giving out a very 

 considerable amount of phosphorescent light. 



If we may be allowed to compare the light of 

 abysmal animals with that of surface forms, we can 

 readily imagine that some regions of the sea may 

 be as brightly illuminated as a European street is 

 at night — an illumination with many very bright 



