Dr Smith on the Waters of the Dee and Don, 809 



foul air evolved by heat expands, and expanding it rises, and rising 

 it would be followed by cold air settling down by the gulley gratings 

 in the streets, thus constituting their inlets downcast shafts, and 

 the sewers and drains themselves channels for the currents setting 

 to the up-cast shafts, by which they would be relieved. The down 

 draught into the sewers would carry with it much soot and fine dust, 

 which would settle upon the liquid current and pass off with it, and 

 so remove some of the tangible as well as the intangible impurities, 

 before referred to, from the air in our streets and about our houses. 

 Much in this way might be effected by the aid of causes in con- 

 stant operation ; but if the up-cast shaft to every house wore also a 

 fire-flue, or wore only aided by the draught of a neighbouring fire, 

 the up-current would be sufficient not only to prevent the house 

 drains from retaining foul air, but the foul air would be thrown off 

 into the upper air with better effect and be dissipated innocuously 

 and without offence instead of steaming as it now does from the 

 sewers into the air where it cannot be avoided. 



On the Composition of the Waters of the Dee and Don , at Aber- 

 deen. By John Smith, M.D., Fordyce Lecturer on Agri- 

 culture in Marischal College, Aberdeen. 



I. — General character of the districts drained by the Rivers Dee 



and Don. 



The sources of the Dee are found amidst the lofty granite 

 mountains of Braemar, on the confines of the counties of 

 Banff, Inverness, and Perth. The river flows from thence, in 

 an easterly direction, along a narrow valley, till it falls into 

 the sea at Aberdeen, its length being about 80 miles, or, when 

 measured in a straight line, 65 miles. The river banks are 

 gravelly, and the alluvial deposits few, and of limited extent. 

 The bounding ridges of the valley are mostly of granite and 

 gneiss. The flow of the water is pretty rapid, the alteration 

 of level between the Lirin (16 or 17 miles below the source) 

 and Aberdeen, being nearly 1200 feet. From the small pro- 

 portion of clay and peat in the valley of the Dee, its waters 

 are usually quite clear ; in rainy weather, however, they are 

 often charged with mud from the swollen mountain-torrents^ 

 The Dee and its tributaries drain about 900 square miles of 

 country. 



The rocks near the sources of the Dee are granite und 



VOL. LI. NO. en. — OCTOBER 1851. X 



