72 
BATHYMETRICAL SURVEY OF 
(53° at 4 p.m.), the thermometer in 3 feet of water then reading 52°'9, 
while that in 1 foot of water read 53°*3. The temperature recorded in 
1 foot of water was lower than that recorded in 3 feet of water in the 
forenoon and late evening, but at noon and 1 p.m. it was higher, at 
2 p.m. and 3 p.m. it was identical, and from 4 p.m. till 8 p.m. it was 
higher, the greatest difference recorded being l°-3 at 9 p.m. (52°*8 at 
3 feet, and 51°-5 at 1 foot). 
The temperatures taken beneath the surface have been collected 
together and arranged chronologically in the foregoing table, which may 
be useful for future reference and comparison. The great majority of 
them were taken in the small 80-feet basin towards the west end of the 
loch, while one series was taken near the east end on April 3, and three 
series were taken towards the middle of the loch, opposite Craiganour, 
on May 1, 2, and 23. The table shows well the heating up of the 
water with the advance of summei-. The readings taken near the west 
end in March are all below 39° Fahr. — that is, below the maximum 
density point, thouglnsurface temperatures exceeding 39°, and in one or 
two cases exceeding 40°, were recorded near the shore during the last 
days of March. On April 2 and subsequently, the temperature was 
above that of maximum density (39°T), but the observations taken near 
the east end on April 3 showed that the temperature of the water from 
surface to bottom was just below maximum density point. The water 
in the small western basin had a temperature under 40° up to April 10, 
and was practically uniform from top to bottom, but on April 21 and 
subsequently the temperature rose, and there was a considerable range 
between the temperature of the upper and lower layers. The water in 
the main basin had a temperature of 40° at 200 and 300 feet on May 1 ; 
on May 2 the temperature was 40°*2 at 200 feet; and on May 23 it 
was 41°' 9 at 100 feet. By the beginning of June the water near the 
surface had attained a temperature of 50°, and by June 21 that 
temperature extended down to 50 feet, the upper 10 feet having on 
that date a temperature of 52°. 
Loch Lyon (see Plate XXI.). — Loch Lyon lies at a high elevation 
at the head of Glen Lyon, amid grand and mountainous scenery, its 
waters being carried by the river Lyon into the river Tay a short 
’ distance above the mouth of Loch Tay ; it contains both salmon and 
trout. It trends in a north-east and south-west direction, and is 
extremely simple both in outline and in the conformation of the bottom. 
It is of nearly uniform width, except for a cone of alluvium, brought 
down by the river, on the south-eastern shore. It is about 1| miles in 
length, with a maximum breadth of over a quarter of a mile, the mean 
breadth being over one-fifth of a mile, or 12 per cent, of the length. 
Its waters cover an area of about 236 acres, or over one-third of a square 
mile, and it drains an area of over 10 J square miles, an area nearly 
