64 DR DAVY ON THE RAIN-FALL IN THE LAKE-DISTRICT. 



Africa,* have fallen over vast tracts of country, at almost incredible distances from 

 their source, and have occasionally been conveyed by upper currents of air, blowing 

 in a direction opposite to that of the prevailing winds. f The smoke which is poured 

 out in such large quantities from the innumerable chimneys in our great manu- 

 facturing towns is of wide range, often reaching the Lake -District, and indeed it 

 may be said normally, so as to occasion the discoloration of the fleeces of the 

 flocks on the higher fells, and not unfrequently to appear as a film on the sur- 

 face of our lakes and tarns4 



In relation to the economy of nature, this diffusion of matter by the agency of 

 the winds and by means of rain, cannot but l)e of importance ; nor, is it, I ap- 

 prehend, without interest as concerns the works of man. It seems, as it were, to 

 establish a circulation of matter, associated with that of the circulation of water, 

 thereby bringing back in part to the land what has been abstracted from it by 

 water, in its descent to the sea ; and thus tending to prevent the exhaustion 

 of soils which are not artificially manured, and which, in wild pastoral dis- 

 tricts, such as our downs and fells, are constantly being depastured. It may help 

 to account too, not only for the continued growth of herbage in the situations 

 just mentioned, during an indefinite term of years, but also for the growth of 

 trees and shrubs unaided by manure, and which is so rapid in the Lake District, 

 where the rain-fall is so great. 



As regards the w^orks of man, the influences of rain, referrible to its contents, 

 seem to be all rather of an unfavourable and destructive, than of a beneficial and 

 preservative and restorative kind ; as tending to promote the disintegration of 

 stone employed in building, of which there are so many striking examples ; and 

 also the decay of wood, and of all tissues, whether animal or vegetable, used in 

 the arts, to which rain has access § On metals too, on all such as are liable to 



* On the 15tli May 1830, there was a remarkahle shower of dust, supposed to have come from 

 the African Coast, which fell over a vast extent of the Meditei-ranean ; it was witnessed ahout the 

 same time of the day at Malta, Sicily, and Sardinia. An account of it is given in my " Notes on the 

 Ionian Islands and Malta," vol. i. p. 300. 



■j" An instance of this kind occurred during the last eruption of the Souffi'iere Volcano, in 

 St Vincent, on the 30th April 1812. Although Barbadoes is sixty miles to windward, volcanic dust 

 on that day, carried by an upper current, fell over the whole extent of the island, and was so dense 

 in falling, as to produce the darkness of night at mid-day, and was in so large a quantity, that I saw 

 remains of it in the soil, where it had not been disturbed, when I was there, thirty-six years after 

 the event. 



I In No. 73 of the " New Edinburgh Philosophical Journal," there is a notice which I com- 

 municated, relative to this sooty deposit ; and in the same paper, I mention, that after Baron 

 LiEBiG, I found ammonia in rain-water, but never, as he did in Germany, obtained any traces of 

 foecal matter. 



§ If a wall for example, one such as I have watched, is not strongly impervious to drifting rain, 

 that portion of rain which penetrates and reaches the inner surface will there evaporate and leave 

 its saline contents, — these always accumulating, and, from their tendency to deliquesce, from attract- 

 ing moisture, must render the surface almost perpetually damp, — a state equally favourable to the 

 decay of paper-lining, and to mildew-growth. 



In the West Indies, at Barbadoes, I have witnessed a like accumulation of saline matter derived 



