TEANSACTIONS OF SECTION A. 529 



the term day of each month from Decemher 1885 to June 1886, in continuation 

 of Mr. J. Y. Buchanan's researches. These included the whole length of Loch 

 Katrine and the head and middle part of Loch Lomond, the deepest sounding, 99 

 fathoms, being got near Inversnaid in the latter lake. 



At Inversnaid, from Decemher till March, the water was each month of uniform 

 temperature from surface to hottom, the temperatures being — 



Dec, 22, 1885 . . 428° 



Jan. 21, 1886 , . 41-2° 



Feb. 23, 1886 . . 40-05" 



March 23, 1886 . . 39-05° 



In the deepest sounding obtained on Loch Katrine, 79 fathoms, a similar distri- 

 bution was met with up till February, the readings beings 



Dec. 23, 1885 . . (42-3°)i 

 Jan. 22, 1886 , . 404° 

 Feb. 24, 1886 . . 390° 



And, though the maximum density point was thus attained in February, uniformity 

 stUl prevailed in March down to a depth of 70 fathoms, the readings on March 24 

 being: surface, 38-1°; 70 fathoms, 38-1° ; 79 fathoms, 38-7°. 



In April the temperature distribution usually found in spring had set in in both 

 lakes, the surface being warmest, the bottom coldest, and the temperature falling 

 more and more slowly with increase of depth. The circumstance of most interest, 

 however, is that the warmth of the bottom layer increased monthly over the deepest 

 parts of both lakes, as follows : — 



Mar. April May June 



Loch Lomond (99 fathoms) . . 3905° 39-4° 40-3° 40-6° 

 Loch Katrine (79 fathoms) . . 38-7° 39-1° 40-1° 4065° 



This rise is evidently due not to the conduction of heat nor to the penetration of 

 solar radiation, but to some drainage or oozing causing mixture. This supposition 

 seems necessary also to explain the behaviour of Loch Katrine in March. Drainage 

 en masse appears to occur chiefly in winter and spring, not in summer when the 

 river water and the lake surface water are much warmer than the deep water of 

 the lake. 



The mean temperature of Loch Katrine probably has a greater range than that 

 of Loch Lomond. 



The shallower parts of the lakes resemble the deep parts as to uniformity of 

 temperature up tOl March. But their yearly range is greater. In both lakes the 

 mean temperature becomes unifonn along the whole length about April 4. 



9. On the Distribution of Temperature in the Firth of Clyde in April and 

 June 1886. By J. T. Mokrison, M.A. 



In the latter parts of April and June of this year Mr. Jojin Murray, Dr. Mill, 

 and the author made serial temperature soundings throughout the Clyde district' 

 chiefly with Negretti and Zambra's reversing thermometer. 



It was found that in matter of temperature the waters of the district were 

 divisible into four groups : I. North Channel and the plateau south of Arran ; 

 II. The Arran and Dunoon open basins; III. The deep sea lochs; IV. The 

 shallow sea lochs. _ The average temperature in each group at every depth was 

 calculated for April and June, and these averages form the basis of this paper. 



In April in all grou]DS there is a deep layer of uniform temperature overlaid by 

 a layer of temperature rising steadily to the surface. In groups II., III., and IV. 

 the uniform deep temperatures are almost the same, about 41-4° F. • in o-roun T 

 it is 41-8° F. , o pi. 



In June the superficial layer of varying temperature had thickened to about 20 

 fathoms. The deep temperatures in the groups were now very difierent: 



' No sounding made here in December. Above temperature is calculated from 

 that of another part of the lake. 



1886. jj jj 



