CLYDE SEA AREA. 59 



represent 14 J hours of sun-work. The actual gain of temperature throughout the whole 

 mass was 0°*2, so that the rate of gain of temperature of 0'*014 per hour for the whole 

 depth of 105 fathoms, or 0°'070 per hour for 20 fathoms. 



Fig. 19, Plate XXV., gives a similar pair of curves for 7th and 8th July 1887. The 

 weather on this occasion was warm throughout, with a southerly or south-westerly 

 breeze, interrupted by light squalls of hot air from the land. On the 7th, the 

 middle of the observation was at 15 h 0, when the air-temperature varied from 63° to 66° 

 in the calms and squalls. On the 8th the observation was at 17 ll 15, and the air- 

 temperature between 68° and 70°, the breeze also being fresher. The tidal phase was 

 thus practically the same on both days (l^ hours' ebb on the 7th, 1^ hours' ebb on 

 the 8th), and the observations were 26^ hours apart. Of this time there were 19 hours 

 daylight and 7 hours darkness, but the sky was frequently clouded. The two curves 

 are identical below 60 fathoms, and from 30 to 60 fathoms run parallel and very 

 close, the later being about 0°'2 warmer. The upper 30 fathoms are very peculiar. 

 If on the second occasion only three observations had been made, viz., at 2, 12, 

 and 31 fathoms, the two curves would have been put down as exact]y the same. 

 The upper 30 fathoms of curve A form a perfect paraboloid — the characteristic curve 

 of heating from above — except for a superficial cooling in the first 3 fathoms, which 

 gives a sharp inflexion. The upper 2 fathoms of curve B complete the symmetry of curve 

 A, but the rest of B is irregular, showing a curious local heating between 2 and 12 

 fathoms, and a much more marked increase of temperature between 12 and 30. The 

 latter portion of the curve is indeed of the inverted type. It is difficult to estimate the 

 average temperature of curve B, as there is scarcely a sufficient number of points in the 

 upper part, but the increase of temperature seems to be about 0°"4. On the assumption 

 mentioned above, this would correspond to a rate of heating for the whole depth of 0°'033 

 per hour of sunlight, more than twice that found for June. The soundings were, how- 

 ever, made in squally weather, and the irregular distribution of temperature layers on the 

 8th must be partly, perhaps mainly, due to the disturbing influence of a cross -channel 

 breeze of hot air setting up irregular movements in the water. 



Fig. 20, Plate XXV., gives the vertical curves for Nos. 22 and 23 of Table XIX., observed 

 on August 14th and 16th, 1887. Curve A on the 14th represents the state of temperature 

 at 19 ll 40 when a light north-westerly breeze was blowing, curve B on the 14th at 15 h 15 

 when there was a very light breeze from the south-west. On both occasions the sun was 

 shining brightly. The observations were 44 hours apart, of which 26 were in daylight 

 and 18 in darkness. Except for a slight excess of heating at the surface, and an 

 apparent cessation of heating at 30 fathoms, the two curves were similar in form and 

 only slightly divergent. They were coincident at the bottom, and the later curve 

 showed 2° of warming at the surface. Were it not for the inflexion of curve A 

 at 30 fathoms, which almost suggests a misreading of the thermometer by one degree, 

 the amount of heating would diminish steadily from surface to bottom. Curve B 

 shows almost the greatest positive slope observed at Skate Island. The average 



