768. ROUND THE WORLD. 21 



shells, only not so full ; its principal food therefore 

 is probably the Helix just mentioned. A current to 

 the N. W. prevailed more or less till Monday the 

 24th, when we were in latitude 1° 7' N., and longi- 

 tude 28° 50'. 



On the 25th we crossed the line with the usual 

 ceremonies, in longitude 29° 30', when, by the result 

 of several very good azimuths, the variation was 

 2° 24'. 



On the 28th, at noon, being in the latitude of 

 Ferdinand Noronha, and, by the mean of several ob- 

 servations by Mr. Green and myself, in longitude 

 32° 5' 16'' W., which is to the westward of it by some 

 charts, and to the eastward by others, we expected 

 to see the island, or some of the shoals that are laid 

 down in the charts between it and the main, but we 

 saw neither one nor the other. 



In the evening of the 29th, w^e observed that 

 luminous appearance of the sea which has been so 

 often mentioned by navigators, and of which such 

 various causes have been assigned ; some supposing 

 it to be occasioned by fish, which agitated the water 

 by darting at their prey, some by the putrefaction of 

 fish and other marine animals, some by electricity, 

 and others referring it into a great variety of different 

 causes. It appeared to emit flashes of light exactly 

 resembling those of lightning, only not so consider- 

 able; but they were so frequent, that sometimes eight 

 or ten were visible almost at the same moment. We 

 were of opinion that they proceeded from some lumi- 

 nous animal, and upon throwing out the casting net 

 our opinion was confirmed : it brought up a species of 

 the Medusa, which, when it came on board, had the 

 appearance of metal violently heated, and emitted 

 a white light : with these animals were taken some 

 very small crabs, of three different species, each of 

 which gave as much light as a glow-worm, though 

 the creature was not so large by nine-tenths : upon 



c o 



