208 RKPORT — 1872. 



Lomond, from observations made by him with a Miller-Casalla tharmometer, 

 three important facts were stated : — 



1. On the 12tli of October, 1871, the temperature at the surface was 52', from 

 which it fell, on descending, till at 300 feet below the surface it stood at 42^; 

 and this temperature of 42^ was uniformly maintained at greater depths, or o 

 518 feet, the depth of tlie loch at the place of observation. 



2. On the 18th of November following, the surface-temperature was 46' ; at a 

 depth of 250 feet 42°-25 ; at 270 feet and lower depths 42°. 



3. On the 10th of April, 1872, the temperature at the surface was 43°, at 150 

 feet 42°- 1, and from 200 to 594 feet 42°. 



Hence it appears that there is a stratum of water of considerable thickness at the 

 bottom of this loch of uniform temperature — that the upper surface of this stratum 

 of deep water of uniform temperature was about 100 feet higher on the 10th of 

 April than it was in the beginning of winter, or on the 18th of November — and 

 that this deep-water temperature probably remains constantly at or very near 42°. 



During this period the temperature was the average of the season on fifty-one 

 days, the deficiency amounting to a mean of 3°-4 ; and above the average on ninety- 

 four days, the excess amounting to a mean of 4^, the most markedly mild periods 

 extending over sixty-nine days, viz. from the lltli of January to the 10th of March, 

 during which the temperature was on an average 3°-9 above that of the season ; 

 and the temperature was, for the whole period of 145 days, l°-4 above the average. 



It may be concluded that in ordinary winters the stratum of water of uniform 

 temperature will be thicker than Sir Robert Christison found it to be this year 

 in the beginning of spring ; in other words, that it will be nearer the surface than 

 170 feet. 



The late Mr. James Jardine, C.E., made observations on the temperature of 

 Lochs Tay, Katrine, and Lomond, in August and September 1812, and again in 

 September 1814, and found the deep-water uniform temperature of the lochs to 

 be 41°-9, 41°-7, and 41°-5, 



These observations were made in the summer and early autumn, or when the 

 temperature of the sea and of the lakes is about the annual maximum. Taken 

 in connexion with Sir Robert Christison's observation, they warrant the conclusion 

 that the deep-water temperature of Loch Lomond remains during the whole year 

 either absolutely at, or very nearly at, the low figure of 42°. 



Mr. Jardine's observations also show that this is not a peculiarity of Loch 

 Lomond, but that it is also a characteristic of Lochs Katrine and Tay, and most 

 probably of other deep waters. 



The mean annual temperature of the air at Loch Lomond, from the mean at 

 Balloch Castle, situated at the foot of the loch, calculated on tlie thirteen years' 

 average ending 1869, is 48°, which is 6° higher than the uniform deep-water 

 temperature of the loch. The deep-water temperature is, therefore, not deter- 

 mined by the mean annual temperature of air over this part of the earth's surface. 



From Forbes's ' Climate of Edinburgh,' it is seen that the temperature there is 

 under the annual mean from the 21st of October to the 26th of April. Assuming 

 that this holds good for Balloch Castle, then the mean temperature of the air for 

 these 188 days is 41°-4. 



The close approximation of this temperature of 41°-4 to 42°, the deep-water 

 temperature of the loch, is such as to suggest that it is the mean temperature of the 

 cold half of the year which determines the temjyerature of the lowest stratum of water 

 at the bottom of deep lakes, so long a? the deep-water temperature does not fall 

 below that of the maximum density of the water. As this principle, if established, 

 would be of great importance in many questions of physical research, such as the 

 deep-water temperature of the Mediterranean Sea, which Dr. Carpenter has ■\ery 

 accurately ascertained, in its connexion with the larger question of general oceanic 

 circulation, it well deserves further investigation. 



Explorations in the Gold Region of tlie Limjyopo. By E. Button. 

 The paper ^'ave an account of journeys made by the author in 1809 across the 

 Limpopo and in the neighbourhood of iLydenburg. After crossing the Limpopo in 



