Ch. XXIII.] CONDITIONS OF LUMINOSITY. 405 



them, they remained upon the table during the night. On 

 stirring the water in the dark, the whole became faintly 

 luminous, giving out a general glow, as if every particle 

 were phosphorescent ; the minute Crustacea, &c. appearing 

 as bright spots in the luminous fluid. If the shmy sub- 

 stance in which, in some marine animals at least, a lumi- 

 nous property appears to reside, become diffused through 

 the water, as it is probable it may be under certain com- 

 binations of conditions and circumstances, a general lumi- 

 nosity of the water may result, similar to that observed in 

 milky sea, while the small sparks, doubtless in great abun- 

 dance, would remain unnoticed in the universal glow, but 

 would at the same time greatly enhance the general luminous 

 effect. 



There is a common idea that a southerly wind is pecu- 

 liarly productive of liuninosity in the sea ; but according 

 to my observations, this is an error. The winds most pre- 

 valent when luminosity has been well marked have been 

 westerly, north-westerly, or even easterly — south being per- 

 haps the least frequent ; but probably the direction of the 

 wind has no special influence in the matter. What the 

 favourable conditions really are, it is as difficult to say as it 

 is in the case of floating animals generally. I have seen 

 remarkable exhibitions on one night followed by nearly 

 absolute darkness on the . next,, the conditions of wind, 

 weather, barometer, and thermometer, being inappreciably 

 altered. Probably temperature is as important as any in- 

 fluence — the luminosity in the Mersey only occurs in sum- 

 mer. And in rounding the Cape of Good Hope during the 

 winter season, scarcely any luminosity was exhibited during 

 the month in which we were passing through the higher 

 degrees of south latitude. 



