61 



this subject : "A solution of one part of sulphate of 

 magnesia in eight of water is the most convenient 

 menstruum for extracting, retaining, and increasing 

 the brilliancy of this light. Sulphate and muriate of 

 soda also answer in a proper state of dilution with 

 water. When any of the saline solutions is too con- 

 centrated, the light disappears, but instantly bursts 

 forth again from absolute darkness by dilution with 

 water. I have frequently made this curious experi- 

 ment with the light procured from whiting. Common 

 water, lime-water, fermented liquors, acids even very 

 dilute, alkaline leys, and many other bodies, perma- 

 nently extinguish this spontaneous light. Boiling water 

 destroys it; but congelation merely suspends its exhi- 

 bition, for it re-appears on liquefaction. A gentle heat, 

 increases the vividness of the phenomenon, but lessens 

 its duration."* These phenomena are by no means 

 incompatible with the idea suggested, as to their 

 dependence on luminous matter, connected with 

 marine animalculae : we know, for instance, in refer- 

 ence to the circumstance of dilution, that when the 

 water which contains the gordius evaporates, it shrivels 

 and dries up ; it may be then preserved for any length 

 of time, but when tranferred to water, it soon lives and 

 moves : a similar thing precisely happens to the 

 rotifer ; and as to the relations of heat and cold to the 

 luminous matter, analogies will be found in the observ- 

 ations and experiments on the light and luminous 

 matter of the glow-worm. 



On opening an oyster, luminous matter, emitting a 

 bluish light resembling a star, has been oberved in the 

 shell ; and, on being taken from the animal, it extended 

 nearly to half an inch in length. Under the lens it 



* " Dictionary of Chemistry," article Light. 



