NATURAL HISTORY OF THE BANKS OF THE TAY. 
85 
These figures represent parts of the substance in every 100,000 
parts of the water. The chief points to note here are 
1. When the river is in full flood, as here, due to the melting of 
snow among the hills, the composition of the water is practically the 
same throughout, as is shown by the solids, the hardness, and the 
chlorine. 
2. The sample No. 7 in the table was drawn at the same time as 
the others, but from the town supply. The flood came down between 
the Monday and Tuesday, the water being low before, and we have 
here an increase in total solids in solution, also in the chlorine, and 
in the hardness, showing that the spate water had not had time to 
pass through the service pipes before the sample was drawn. 
3. The temperature of the air is in all cases higher than that of 
the water, which is what one would expect, as a large volume of the 
water is got from melted snow. In addition, it is interesting to note 
that the general difference in temperature is greater in the early part 
of the day and gradually decreases during the afternoon. 
4. The amount of solids in suspension shows, we think, that in 
flood the Tummel must contribute a large quota of the muddy matter, 
and that this is carried in large quantity through the Pass of Birnam 
and down the length of Delvine. At Campsie the river has been 
joined by the Isla, and is flowing at a much slower rate, so that the 
heavier matters in suspension have settled down, and amount to little 
more than half of what we found in suspension at Delvine. This 
diminution goes on all the way to Inchyra, and is interesting geo¬ 
logically as showing the action of water as a denuding agent, and its 
further action as the agent by which river islands, deltas, and allu¬ 
vial soils have been deposited. 
Let us next examine the second set of analyses, which are more 
valuable in the way of giving us a general impression of the water in 
the Tay under normal conditions. These samples were drawn from 
the different points mentioned, on May 2nd when the river was low, 
and the water clear, and free of suspended impurities except in the 
samples drawn at Inchyra and Newburgh, where the mud found was 
evidently stirred up from the bottom of the river. 
