THE PYROSOMA. 55 



gitude 27° 5' west, having fine weather, and a fresh 

 south-easterly trade wind, and range of thermometer 

 being from seventy-eight to eighty-four degrees, late 

 at night the mate of the watch came and called me to 

 witness a very unusual appearance in the water, which, on 

 first seeing, he considered to be breakers. On arriving 

 upon the deck, this was found to be a very broad and ex- 

 tensive sheet of phosphorescence, extending, in a direc- 

 tion from east to west, as far as the eye could reach ; the 

 luminosity was confined to the range of animals in this 

 shoal, for there was no similar light in any other direction. 

 I immediately cast the towing-net over the stern of the 

 ship as we approached nearer the luminous streak, to 

 ascertain the cause of this extraordinary and so limited 

 a phenomenon. The ship soon cleaved through the 

 brilliant mass, from which, by the disturbance, strong 

 flashes of light were emitted ; and the shoal (judging 

 from the time the vessel took in passing through the 

 mass) may have been a mile in breadth : the passage 

 of the vessel through them increased the light around 

 to a far stronger degree, illuminating the ship. On 

 taking in the towing-net, it was found filled with pyro- 

 soma, which shone with a beautiful pale greenish light. 

 After the mass had been passed through, the light 

 was still seen astern, until it became invisible in the 



