PHOSPHORESCENCE. 13 
exception, and not the rule with similar Medusz, 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 followmg experiments, instituted on a species of Thaumantias, 
with the view of ascertaining the effects of various irritating conditions :— 
“1. Some hemispherical Medusz 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 Medusz 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 Medusz, 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 hemispherica 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 Medusze 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 Medusz 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 Meduse, 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 T’haumantias into fresh water or spirits call forth 
the dormant phosphorescence suddenly, and with extreme vividness. It gradually fades away 
* His notes will appear in the account of the Niger Expedition by Capt. Allen and Dr. Thompson. 
+ Phil. Trans., 1810. 
