of Edinburgh, Session 1871 - 72 . 
569 
mediate weather having been generally fine, I found, with the 
same thermometer, in 96 feet of water, near the head of the 
lake, 56° at the surface and 54° at the bottom; and in 144 
feet of water, in the middle of the loch, exactly opposite the 
17th milestone from Selkirk, I obtained 55° at the surface and 
47° at the bottom. During three of the warmest months of last 
warm season, the heat of the earth, or the sun’s rays, had heated 
the water at the bottom by one degree of Fahrenheit only. I do 
not well see how that water can ever rise from such a depth, unless 
its temperature during the winter should fall below 39°*5, which 
is not probable. 
I regret I did not take successive observations at several depths 
in order to fix the upper limit of the cold substratum of water. My 
time was short, for my main object on that occasion was the changes 
undergone by the river Yarrow, and I contemplated a chain of 
observations in more favourable circumstances at Loch Lomond. 
I went to Loch Lomond on four occasions for the purpose, viz., on 
September 14th, September 21st, October 11th and 12th, and 
November 18th. As accurate observations were made only on the 
two last occasions, I shall refer to the others only incidentally. 
On 11th October, at 3 p.m., the atmospheric temperature on land 
being 48°, and that of the surface water everywhere over deep sound¬ 
ings 52°, I found in 103 fathoms of water opposite Culness, with a 
Six’s thermometer by Casella, which, though not specially protected 
against high pressure, was believed to be proof against such pres¬ 
sures as it was to be subjected to, that a temperature of 43° was 
indicated at 200 feet, and 41°‘8 steadily at 400, 500, and 618 feet. 
Next forenoon at 11,1 repeated my observations about a mile lower 
down opposite Tarbet in 87 fathoms. The air was singularly still, 
the atmospheric temperature on land 44°, and that of the loch on 
the surface 52°, exactly as on the previous day. The following 
successive temperatures were obtained at various depths:— 
Surface, . 
. 52°-0 
150 feet, 
. 44°-5 
25 feet, . 
. 51°*5 
200 „ 
• 
. 43°'0 
50 „ . 
. 50°*2 
CO 
o 
o 
• 
. 42°-0 
75 „ . 
. 50°'0 
400 „ 
• 
. 42°*0 
100 „ . 
. 49° 5 
518 „ 
bottom 
i, . 42°-0 
VOL. VII. 4 G 
