PHOSPHORESCENCE. 13 



exception, and not the rule with similar Medusse, on the coast of Cornwall. Spallanzani 

 fancied that the higher Medusa, Pelagia phosphorea, always emits light more or less, but his 

 own experiments go far to disprove the notion. My friend and countryman Dr. I. Heywood 

 Thompson, R.N., has, during his voyages on the western coast of Africa, and elsewhere in 

 tropical and in southern seas, paid careful attention to the phenomenon of phosphorescence of 

 the sea, and has never observed it, when the product of animal life, to occur, except under 

 circumstances of irritation.* 



Macartney narrates the following experiments, instituted on a species of Thaumantias, 

 with the view of ascertaining the effects of various irritating conditions : — 



" 1 . Some hemispherical Medusae were put into a spoon, containing a small quantity of 

 sea-water, and held over a burning candle. As soon as the water became heated 

 the Medusae appeared like illuminated wheels, the spots at the margin and centre 

 alone emitting light, in which manner they shone vividly and permanently for about 

 20 seconds, when they shrunk and died, after which they were no longer luminous. 

 "2. Some of the same species were put into spirits : a strong and unremitting light was 

 instantly given out, which issued from the central and marginal parts, as in the 

 preceding experiment, and continued until they died. 

 " 3. Some of the scintillating and hemispherical species of Medusae, contained in a small 

 glass jar, were introduced into the receiver of an air-pump, and the air being 

 exhausted, they shone as usual when shaken ; if any difference could be perceived, 

 the light was more easily excited, and continued longer in vacuum. 

 " 4. A Medusa hemisphtBrica was placed in a small glass dish, containing a quantity of 

 water, merely sufficient to allow the animal to preserve its figure ; being insulated, 

 it was electrified and sparks drawn from it, which had not the slightest effect ; the 

 experiment was repeated several times with different individuals, but without exciting 

 the animals to throw out light. 

 " 5. Some hemispherical Medusae were placed in contact with the two ends of an 

 interrupted chain, and slight electric shocks passed through them. During the very 

 moment of their receiving the shock no light was visible, but immediately 

 afterwards the Medusae shone like illuminated wheels, which appearance remained 

 for some seconds. Upon the closest inspection with a magnifying glass, no motion 

 could be perceived to accompany the exhibition of light. The application of 

 electricity in this instance seems to have acted as a strong mechanic shock."! 

 Ehrenberg placed the same species in spirits, with a view to observe the effect, and found 

 the phosphorescence brilliantly revived when it had ceased to be exhibited by ordinary modes 

 of irritation. 



Spallanzani had, previous to either, instituted similar experiments with those described 

 by Macartney, but on one of the higher Medusa, the Pelagia only. He found raising the 

 temperature revive the phosphorescence, when it had otherwise ceased to appear. 



I have found the sudden plunging of Thaumantias into fresh water or spirits call forth 

 the dormant phosphorescence suddenly, and with extreme vividness. It gradually fades away 



* His notes will appear in tlie account of the Niger Expedition by Capt. Allen and Dr. Thompson, 

 t PhU. Trans., 1810. 



