■2jo Mr. Macartney’s Observations 
on being brought again into contact, like globules of quick- 
silver. The globules, he says, were so transparent, that they 
could not be perceived when the hand was taken into the 
light. 
This extraordinary appearance of the sea was visible for 
two nights. As soon as the moon exerted her influence, the 
sea changed to its natural dark colour, and exhibited distinct 
glittering points, as at other times. The phenomenon, lie 
says, had never been witnessed before by any of the com- 
pany on board, although some of the crew had been two or 
three times round the globe. 
I consider this account of Mr. Langstaff very interesting 
and important, as it proves that the diffused light of the sea 
is produced by an assemblage of minute medusae on the 
surface of the water. 
In June 1806 , 1 found the sea at Margate more richly stored 
with the small luminous medusae, than I have ever seen it. 
A bucket of the water being set by for some time, the 
animals sought the surface, and kept up a continual sparkling, 
which must have been occasioned by the motions of indi- 
viduals, as the water was perfectly at rest. A small quantity 
of the luminous water was put into a glass jar, and on stand- 
ing some time, the medusae collected at the top of the jar, 
and formed a gelatinous mass, one inch and a half thick, and 
of a reddish or mud colour, leaving the water underneath 
perfectly clear. 
In order to ascertain if these animals would materially alter 
their size, or assume the figure of any other known species 
of medusa, I kept them alive for 25 days, by carefully changing 
the water in which they were placed ; during which time. 
