86 Dr. Collingwood^ on Microscopic Alga. 



name, while other observant travellers have mentioned it as a 

 singular phenomenon of somewhat rare occurrence, giving 

 the date, and latitude, and longitude of the event. Thus 

 Darwin, who circumnavigated the globe, and was five years 

 at sea, cites but two occasions on which he observed it, viz., 

 near the Abrolhos islets, and off Cape Leeuwin ; the conferva 

 seen near the Keeling Islands having been of quite a different 

 character. 



One circumstance much dwelt on by those who have de- 

 scribed this substance is the red colour it imparts to the sea, 

 so much so, that whether it is De CandoUe who examines 

 the waters of the lake of Morat, or Ehrenberg at the Bay of 

 Tor, or Montague describing the dried specimens which had 

 been obtained from the middle of the Ked Sea, they all agree 

 in calling it erythrmmn, or rubescens, while Ehrenberg im- 

 proves upon this by naming De Candolle's species Oscillatoria 

 Pharaonis, from a E-enanish idea that this is the natural ex- 

 planation of the waters turned into blood in the plagues of 

 Egypt. It is described by some as blood-red, by others 

 orange- red, or brick-red Avhen expanded over a large surface, 

 and we are assured that the Red Sea or Mare eythrseum of 

 the ancients, Bahr Souph of the modern Arabs, is so called 

 from this red Alga, the Arabic name simj)ly meaning Mare 

 algosum. 



I do not for a moment call in question this red apj)earance 

 which seems to have been so often observed in the Ked Sea, 

 but I only wish to remark that numerous as have been the 

 occasions on Avhich it has been my fortune to observe the sea 

 to be discoloured by a floating Alga, in the Eastern and 

 Western Hemispheres, I have never at any time seen it 

 approach a red colour, much less assume the rovge de sang 

 of the French writers. The only time I ever saw the sea of 

 a blood-red colour was in a limited space in the Formosa 

 Channel, when I satisfied myself that the red appearance 

 was due to myriads of minute gelatinous worms which filled 

 the Avater. 



In passing down the Red Sea, indeed, although during a 

 week always on the look-out, I saw r\,o trace of red or any 

 other discoloration. This was early in March. Ehrenberg's 

 observations were made in December and Janviary ; Dupont's 

 in July ; and De Candolle's " at the end of winter." It was 

 not till 1 was in the Indian Ocean, in long. 70° E. and lat. 

 5° N., that 1 first observed that the sea had, as I entered it 

 in my journal, a dusty appearance, as though myriads of 

 minute bodies were floating in it, not all upon the surface, 

 but at various depths beneath. This appearance was rendered 



