288 PHOSPHORESCENCE. SECT. XXVIII. 



degrees ; the phosphorescent parts then shine brilliantly, 

 and the dark lines appear black. 



Since the parts of similar refrangibility in the differ- 

 ent spectra are traversed by the same dark lines, rays 

 of the same refrangibility are probably absorbed at the 

 same time by the different media through which they 

 pass. Multitudes of fish are endowed with the power 

 of emitting light at pleasure, no doubt to enable them 

 to pursue their prey at depths where the sunbeams can- 

 not penetrate. Flashes of light are frequently seen to 

 dart along a shoal of herrings or pilchards ; and the 

 Medusa tribes are noted for their phosphorescent brill- 

 iancy, many of which are extremely small, and so nu- 

 merous as to make the wake of a vessel look like a stream 

 of silver. Nevertheless, the luminous appearance which 

 is frequently observed in the sea during the summer 

 months cannot always be attributed to marine animalcule, 

 as the following narrative will show : 



Captain Bonnycastle, coming up the Gulf of St. Law- 

 rence on the 7th of September, 1826, was roused by 

 the mate of the vessel in great alarm from an unusual 

 appearance. It was a starlight night, when suddenly 

 the sky became overcast in the direction of the high 

 land of Cornwallis country, and an instantaneous and 

 intensely vivid light, resembling the aurora, shot out of 

 the hitherto gloomy and dark sea on the lee bow, which 

 was so brilliant that it lighted everything distinctly, even 

 to the mast-head. The light spread over the whole 

 sea between the two shores, and the waves, which be- 

 fore had been tranquil, now began to be agitated. Cap- 

 tain Bonnycastle describes the scene as that of a blazing 

 sheet of awful and most brilliant light. A long and vivid 

 line of light, superior in brightness to ,the parts of the 

 sea not immediately near the vessel, showed the base 

 of the high, frowning, and dark land abreast : the sky 

 became lowering and more intensely obscure. Long, 

 tortuous lines of light showed immense numbers of very 

 large fish darting about as if in consternation. The 

 spritsail-yard and mizen-boom were lighted by the glare, 

 as if gas-lights had been r burning directly below them ; 

 and until just before dayoreak, at four o'clock, the most 

 minute objects were distinctly visible. Day broke very 



