CLYDE SEA AREA. 



105 



Beacon bearing S. ^ mile. The depth was 23 fathoms, the fall from the bar at the 

 mouth of the loch off Eow Point being very abrupt to this point, but the loch then remains 

 almost of the same depth, forming a single trough all the way to the head. The average 

 density of surface water from four observations was 1*02254, maximum 1*02387, and 

 minimum 1*01985 ; and on the bottom the mean from five observations was 1*02341, 

 with a maximum of 1*02380, and a minimum of 1*02239. 



The surface water is practically identical in salinity with that of Row I., but the 

 bottom water is considerably fresher, as might be expected. 



Table XXXIX. — Temperature Observations at Roiv II. 



No. . . . 



1 



2 



3 



4* 



5 



6 



7 



8 



9 



10 



11 



12 



13 



14 



15 



16 



Date . . 



13.4.86 



16.6.86 



4.8.86 



11.11.86 



28.12.86 



2.2.87 



25.3.87 



6.5.87 



13.6.87 



6.8.87 



30.9.87 



29.11.87 



9.2.88 



28.3.88 



7.6.88 



6.9.88 



No. ofPts. 



5 



4 



7 



4 



6 



6 



3 



4 



3 



6 



4 



3 



6 



3 



6 



3 



Temp. . . 



41-8 



48-3 



52-6 



49-4 



44-4 



42-9 



42-9 



45-9 



50-6 



57-6 



53-9 



46-6 



44-0 



41-9 



46-3 



54-1 



Slope . . 



+ 1-6 



+ 1-0 



+ 0-6 





-1-3 



-1-0 1 o-o 



+ 0-9 



+ 1-0 



+0-4 



-0-1 



-1-8 



-0-3 



-o-i 



+ 1-3 



+ 1-3 



* To 10 fathoms only. 



Three observations, those of December 1886, February 1887, and February li 

 show mixed slopes indicating the existence of intermediate layers at different tempera- 

 tures. Nos. 1, 2, and 3 showed positive slope with diminishing range, the greatest 

 range of the whole series being No. 1 of 2°*7 ; at surface, 44°*1 ; at bottom, 41°*4 ; and 

 of this there was a range of 2° in the first 4 fathoms. The small maximum range of 

 2°*7 in 20 fathoms is a distinct feature of this set of curves. 



In order to determine the relation to season of the positive and negative slopes, a curve 

 (fig. 44, Plate XXX.) was constructed, showing positive slope by the difference (drawn 

 above mean line) between the warmer upper 5 fathoms and cooler lowest 5 fathoms ; 

 and negative slope by the difference between the colder upper 5 fathoms and warmer 

 lower 5 fathoms. 



Fig. 44 shows the seasonal change of slope for both Row II. and Shandon. At both 

 stations the curve of slope cuts the zero line about the equinoxes, showing that as long 

 as the period of daylight is greater than that of darkness, the surface water as a whole 

 is warmer than that beneath ; but when the period of darkness exceeds that of daylight, 

 the surface water becomes colder than that below. The period of greatest negative slope 

 appears to occur in December about the time of the winter solstice. In 1886 the maximum 

 positive slope occurred nearly at the summer solstice, but in both the other years it was 

 delayed until the month of August, showing that the surface water continued to gain heat 

 rapidly for two months after the summer solstice. The curve cut the zero line in 

 ascending at or before the annual minimum of temperature, and cut it in descending at 

 or after the annual maximum. 



The curve of seasonal change of mean temperature ran on the whole parallel to that 



VOL. XXXVIII. PART I. (NO. 1). O 



