OF WATER FOR ORGANIC MATTER. 67 



ably rapid whenever the Clyde widens, as at Greenock to 

 Gourock; so that, even near Helensburgh, the number 

 has fallen to 0*0000125 per cent, oxygen by weight, or 

 0-875 grain per 100 gallons. This change, from 0*000045 

 or 3*15 grains per gallon, has been effected in the space of 

 about 2 or 3 miles. Is it possible, then, that the slight 

 further change required demands all the wide distance 

 between Gourock and Arran? I think not. The reason 

 we do not find the number for oxygen falling below O'ooooi 

 per cent, by weight, or 0*7 grain per 100 gallons at Holy 

 Loch, Strone, Dunoon, and Cove, may be seen by exa- 

 mining the Lochs. We there find that they themselves 

 send in water with the oxygen number O'OOOOi per cent, 

 by weight, or 0*7 grain per 100 gallons. 



'^ At this point we must remember that the oxygen may 

 not all be required for putrid matter, and that the streams 

 contain some peaty matter which may also instantly require 

 oxygen. At any rate we know this, that, for whatever they 

 do require it, it can be for the destruction of no very 

 unwholesome matter in the water, as the highland streams 

 must be considered free from such taints. There is a 

 little of the soil of cattle when the weather is wet, but 

 perhaps none when the weather is so dry that the water 

 must pass through the earth before reaching the bed of 

 the stream. 



" We cannot, then, expect the sea-water to demand less 

 oxygen than the streams and lochs that affect it here. In 

 other words we discover the influence of the land on the 

 drainage from the hills, even when all trace of the in- 

 fluence of Glasgow has gone. This is, I believe, the rea- 

 son that, according to circumstances, such as currents and 

 weather, we observe the water of the Firth sometimes as 

 pure as the deep sea, and at other times less so. At Wemyss 

 Bay, for example, the Table does not show this very well. 

 This will happen at other parts of the coast when the 

 streams enter purer than the usual sea-water there, as, for 

 example, at Dunoon and Innellan, where the water flows from 

 streams equal, when not in flood, to the deep Firth water. 



p2 



