CLYDE SEA AKEA. 89 



The curves, like those for shallow water in all parts of the Area, may be classed 

 roughly into two groups, — the equinoctial occurring in spring and autumn, when homo- 

 thermic conditions prevail, both being a straight line (the vernal occurring at the annual 

 minimum, the autumnal somewhat after the annual maximum) ; and the solstitial, 

 characterised by great slope, the summer (during the months of heating) being positive, 

 the winter (during the months of cooling) being negative (see fig. 38, Plate XXIX.). 



The homothermic curves for this station are Nos. 1 (April), 4 (September), 14 

 (November), 16 (February), 17 (June). No. 7 (March) very nearly conforms to the 

 type. Of these No. 17 (June) is abnormal, occurring during rapid heating, and 

 its homothermicity is due not to seasonal change, but to local and temporary mix- 

 ture. 



Of the summer solstitial curves, the form was paraboloid on two occasions, — No. 10. 

 which showed a steady diminution of the rate of fall of temperature from surface to 

 bottom, and No. 12, which was not sufficiently defined to speak certainly of. No. 9 was 

 nearly of the same form, but differed by a rapid fall at the bottom. Nos. 18 and 19 

 also, except for flattening at the bottom, agree fairly with the type. No. 2 is a double 

 parabolic curve, showing the division of the water into four zones, of rapid fall, nearly 

 constant temperature, rapid fall, and nearty constant temperature. Nos. 8, 11, and 20 

 are paraboloid, except for a layer of constant temperature on the surface, in two cases 

 showing surface cooling and an intermediate maximum. In these cases the most rapid 

 change of temperature with depth took place well below the surface, but in all other 

 cases the surface layer showed most rapid change. The steepest superficial gradients 

 were 5°"6 in the first fathom, 7° in 2 fathoms (3°'5 per fathom) in No. 18 (24.8.88); 

 8°'6 in 3 fathoms (2 0> 9 per fathom) in No. 19 (25.8.88); 4°-2 in 1 fathom, or 8°'3 in 

 3 fathoms in No. 9 (16.6.87) ; 3° "2 in 1 fathom, or 11° in 3 fathoms (3° 7 per fathom) in 

 No. 10 (8.7.87) : 3° in 1 fathom (Nos. 3 and 20) is the maximum for those with a slight 

 surface gradient. 



The negative solstitial curves show the paraboloid form of a rapidly cooling surface 

 layer resting on a uniformly warm mass in Nos. 7 and 13 (March and November 

 respectively). No. 15 (December) shows a nearly uniform rise from surface to bottom 

 with intermediate pauses, maximum gradient 4° '4 in 1 fathom (from 1 fathom to 

 2 fathoms). No. 5 is an interrupted paraboloid, showing fall of 6° "4 in 1 fathom (0 to 

 1 fathom), and 3°'4 in 1 fathom (from 2 to 3 fathoms). No. 6 (February) is remarkable 

 as being the minimum for the season, and shows a range of 4°*4. This range is com- 

 pounded of 3° -4 fall in the first 3 fathoms, and 1° fall in lowest 5 fathoms. The inter- 

 mediate zone of 9 fathoms had constant temperature ; as the whole mass might be 

 expected to have at that season. Curves- 13 and 14, observed on November 5th and 7th, 

 1887, are strikingly different. On the 5th it was calm, with average temperature 49° - 5, 

 surface at 46°, bottom at 50°'l ; temperature of 49°-5 occurring at 4 fathoms. The 

 7th was a day of strong north-east wind, blowing directly down the loch ; the mean 

 temperature was 49°-6, the surface 49°7, the bottom 49°'5, and the temperature 



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



