102 EMISSION OF LIGHT BY 
When these dead fish are placed in sea-water, 
they render it luminous in the course of a few 
days,—the phosphorescence of the sea is however 
owing to a different cause,—and the water then 
shines in a uniform manner, 7.c. everywhere with 
equal intensity: if it be passed through a filter it 
continues to shine as before. These facts prove 
clearly that this smgular phosphorescence is not 
owing to any luminous animalcules. 
Water that has been rendered luminous by 
dead fish loses its transparency, becomes milky, 
and acquires a repulsive odour; in the space of 
four or five days it ceases to be luminous. 
Hulme, who has made numerous observations 
on this particular case of phosphorescence, says 
that the luminous greasy substance of the herring 
soon loses its phosphoric properties in pure water. 
Alcohol, acids, and alkalis also prevent its shining. 
Common salt and honey appear, on the contrary, 
to assist this phosphorescence. Sometimes also, 
when the latter has been extinguished by one 
means or another, it can be brought back again: 
thus, in one of Hulme’s experiments, twenty-four 
grammes of sulphate of magnesia, dissolved in 
twenty-one grammes of water, and mixed with 
the luminous substance of the mackerel, com- 
pletely extinguished its hght; but if to this mix- 
ture six times its volume of water were added, it 
became luminous again.. The same observer also 
