7 8 Mr. Thompson on an Alga which colours Bally drain Lake. 



to use their own words, it presents " figures assez semblables a 

 celles produites par lYlectricite positive sur l'electrophore*." 

 In sheltered places there were floating pale blue tufts or small 

 masses, such as I saw here last autumn; but endeavouring to 

 secure them by carefully putting beneath a sheet of paper on 

 which to lift them, I was surprised to find, that notwithstand- 

 ing their apparent consistency, they floated off in the water 

 with which they were brought up, not even leaving behind a 

 tint of their colour. Some specimens from deep water, brought 

 home today, when viewed under the microscope, exhibited 

 precisely the appearance the plant did in July, 



Sept. 26. — On visiting the lake this afternoon, which was 

 fine, though dull and without sunshine, (as the earlier part of 

 the day had been.) I remarked that the water generally had 

 lost some degree of its opacity and looked clearer than on the 

 16th. Instead of the beautiful appearance which the surface 

 presented upon that day, there was in some places merely a 

 little scum, which excepting its very pale greenish tinge, re- 

 sembled precisely the appearance remaining on the surface of 

 water in which ice has been dissolved. Towards the edge of 

 the lake, there were in some places, as on the 16th, gelatinous 

 tufts of a pale blue colour ; in one place crowded together in a 

 mass which covered an area a few yards in extent. These 

 were generally of greater consistence than on the 16th. The 

 portion nearest the edge had, apparently from decay, become 

 ferruginous, and strongly tinged with rust colour the paper on 

 which it was placed, but with the greatest pains I could hardly 

 obtain a trace of the blue colour. The masses, both blue and 

 ferruginous, were very slippery to the touch, about an inch in 

 thickness, and of considerable consistence, more so than sea- 

 jellies or Medusa generally are, or like that of an oyster ; and 

 on being lifted out of the water in a wire-gauze net, remained 

 there without diminution by dripping off or otherwise : their 

 weight too was great. When brought near they had somewhat 

 of the offensive smell of water in which flax had been steeped, 

 and at a short distance from one part of the lake this disagree- 

 able odour was sensibly perceived. 



* Memoires Soc. Physiq. et d'Hist. Nat. de Geneve, t. iii. part 2. p. 31. 



