28 Dr Davy on a Carbonaceous Deposit or Film, ^c. 



the desert, and volcanic sand, and the spray of the sea, have 

 been carried by the wind, it is easy to conceive that soot, the 

 matter of smoke, may be wafted through the atmosphere, 

 even farther than is required, on the supposition that the 

 main source of the film in question is the adjoining manufac- 

 turing districts. 



Liebig has detected in the rain water of Germany, besides 

 carbonate of ammonia, fecal matter, that is, the odour of this 

 matter. I have examined many samples of rain water col- 

 lected at Ambleside, and have always detected in them am- 

 monia, but never the offensive smell alluded to. I have found, 

 too, it may be remarked, collected in the funnel of my rain- 

 gauge, to the terminal pipe of which a piece of linen is 

 fastened as a filter, a notable portion of soot, exactly resem- 

 bling the matter of the pellicle of the lakes. But, though 

 I believe that the greater part of it was brought from a 

 distance, I would not insist on this, inasmuch as it may be 

 said to have been derived from the smoke of the adjoining 

 village. 



I have made no mention of the quantity of black matter 

 observed on the Westmoreland lakes, or on its duration. Its 

 duration is generally short, disappearing after disturbance of 

 the water by the first heavy wind, when being wetted by the 

 agitation, it is probably diffused through the water, and 

 shortly sinks. Its quantity is often considerable, quite pre- 

 cluding the idea of its being derived from the villages and 

 hamlets of the country ; and is of such common occurrence, 

 especially on Windermere, that some gentlemen keeping plea- 

 sure-boats, from its blackening effect, have ceased, I am in- 

 formed, to paint the bottoms of them white. 



The Windermere boatmen, with whom the appearance is 

 familiar, imagine that the black matter rises from the bottom 

 of the lake; a supposition which can hardly be maintained, 

 being incompatible with the specific gravity of the substance 

 when wet, when, as I have already observed, the matter of the 

 film sinks in water. Another supposition regarding its origin, 

 which at first view seems more probable, is, I believe, equally 

 untenable, viz., that the black matter is of the nature of peat, 

 and is washed down from the hills from beds of peat. The 



