ROMANCE OF DEPTHS OF THE SEA 103 



" The sun's perpendicular rays 

 Illumine the depths of the sea." 



But the poet is only partially right ; the sun's 

 rays do not really reach the depths. Till the 

 transatlantic voyage of the " Michael Sars," the 

 limit to which light penetrated the ocean water 

 was generally thought to be at about 300 fathoms. 

 But Dr. Helland-Hansen, the Physical Oceano- 

 grapher of the vessel, has devised a new and 

 more perfect photometer than any that has 

 hitherto been used at great depths. At its very 

 first trial, near the Sargasso Sea, the apparatus 

 acted perfectly. As far down as 500 fathoms the 

 photometer registered light, and in considerable 

 quantities ; but at a depth of roughly 850 fathoms 

 the most highly sensitive photographic plates were 

 unaffected even after an exposure of two hours. 

 Very sensitive pan-chromatic plates were used, 

 and the result of the experiments made at noon 

 on January 6th, 1910, with a clear sky, show 

 that a good deal of light penetrates " to a depth 

 of 1,000 metres considerably deeper than was 

 previously supposed/' At 50 fathoms the rays 

 were of all colours, though red rays were beginning 

 to fade out ; at this depth the red rays were in 

 fact fewer in number than the green ; blue and 



