Red SuhJlanCe olferved on a Pijh-Pond in Norivay. ^97 

 medium, may be known. The friAloa of the index is the 

 only fridion to which the inftrunlent is fubjeft ; but it is fo 

 fmall that it may be confidered as of no confequence. When 

 the index is woril out, its place may be eafily fupplied by a 

 new one. It may be readily comprehended that, by adding 

 a hook to the perforation at the extremity of the divided arc, 

 and a ring in the eye of the ftopper, the inflrument may be 

 employed for weighing. 



XIV. Account of a Red SuhJlance olferved on the Surface of 

 a Fi/b-Po]id in Norway. By Frofeffor H. St ROM *, 



I 



N the fpringoftheyear 1790, a pellicle, orfubftance of a 

 red colour, was obferved on the water at one end of a fifh-pond 

 in Norway, which foon after began to fpread till it covered 

 the whole furface. During dry and warm weather, the red' 

 colour was more perceptible than when it was cold and wet. 

 It was more vifible alfo at noon, than in the morning and 

 evening. I, however, did not pay much attention to it 

 until the colour, about the end of June and the beginning 

 of July, became ftronger than it had ever been before ; it 

 was ftrongeft at noon, and always proceeded, in regular 

 order, from the end of the pond till it gradually extended 

 over the whole furface. I filled a beer glafs with the water^ 

 which had a red appearance in the glafs ; but the red matter 

 foon depofited itfelf at the bottom, and the water became 

 yellowifli: for a long time, however, it had a frothy pellicle, 

 which was fomctimes of a red and fomctimes of a green 

 colour. I let fall a drop of this pellicle on my microfcope, 

 and beheld the Angular phenomenon exiiibited m the an- 

 nexed engraving, (Plate IX. fig. 2.) which reprefents thi4 

 drop as fecn whtn magnified. 



* From tuviJaSiom of the Socitij of Balural-iiifiorj at Copenhagfn^ 

 \ol. l.Part 2. 

 . ^ Q I behclJ 



