Prof. Decandolle on a New Species of Oscillatoria. 307 



which their existence can be determined only by the total de- 

 struction of the circular polarization, which is possessed in an 

 opposite manner by each pair of the combined crystals. 

 I am, Sir, 



Yours most faithfully, 



D. Brewster. 

 Edinburgh, 10, Coates Crescent, 

 March 1, 1827. 



Art. XXXI.- — Account of a New Animal, which occurred in 

 such quantities as to dye Red the Lake of Morat in the 

 Spring o/*1825.* By Professor Decandolle. 



About the end of the winter of 1825, the Lake of Morat pre- 

 sented the remarkable phenomenon of being covered in several 

 places with a red substance, which coloured it in a manner so 

 extraordinary that all the inhabitants on the banks of the river 

 were struck with astonishment. Although this phenomenon has 

 only now attracted particular notice, yet it is said to happen 

 every spring, and the fishermen express the fact by saying, that 

 the lake is in Jlower. In 1825 it lasted from November till 

 March, April, and even May, — a circumstance which is ascribed 

 to the mildness of the winter, and to the low state of the waters, 

 which favours the developement of the organic matter which 

 produces the red colour. 



During the first hours of the day nothing particular is ob- 

 served in the lake, but soon afterwards there are seen long red 

 lines, very regular and parallel, along the margin of the lake, 

 and at some distance from its banks. The winds push this 

 matter into the small bays, and heap it round the reeds, where 

 it covers the surface of the lake with a fine reddish foam, form- 

 ing strata of colour varying from a greenish black to the most 

 beautiful red. Sometimes yellow, red, and grey colours of all 

 kinds are seen, sometimes they are seen marbled, and sometimes 

 they present figures like those produced by positive electricity 

 on the electrophorus. During the day this mass exhales a 



* Abridged from the Mem. de la Soc. de Phys. et D'Hist Nat. de Ge~ 

 neve, torn. iii. part ii. 



