18 DR HUGH ROBERT MILL ON THE 



where the Channel was 52° '5. And, as before, the deep isolated loch-basins retained 

 still colder water, the minimum temperature being 43° in Loch Fyne. The minimum 

 there occurred, as in June, about half way between surface and bottom, the vertical 

 curves being sickle-shaped. The maximum effect of sun-heating was shown near the 

 head of the lochs and in the southern branches of the Arran Basin. 



During this period the temperature in the North Sea, off the mouth of the Firth of 

 Forth, was about 52° from surface to bottom, more than a degree colder than off the 

 mouth of the Clyde Sea Area. 



From August 24th to 30th a short trip was taken in the Dunoon Basin and Loch 

 Fyne, and a few observations were also made in the Arran Basin and Loch Fyne from 

 September 13th to 17th. The data obtained fall into their natural places in discussing 

 the separate stations and regions. They served to fix the period of surface maximum 

 temperature for the year, but are not otherwise of general interest. 



Trip IV., September 1886. — The general climatic conditions of this trip, lasting from 

 the 22d to the 27th, are given in Part II. p. 680. It occurred forty-eight days later than 

 Trip III. Air-temperature was a little below the normal during August and September, 

 and the w T eather was fine on the whole, although rather rainier than the average. From 

 September 10th to 2 2d an anticyclone prevailed, with very light airs, and during the 

 greater part of the trip there was a calm. A cyclone passing from the 25th to the 27th 

 brought a fresh westerly breeze, blowing transversely to the Central Arran Basin and 

 Loch Goil while these regions were being examined. This trip may be said to have 

 been taken at the period of the annual maximum : the maximum for the surface water 

 was past, and cooling had just commenced, but the maximum of the deeper layers was 

 not yet reached. The oceanic water was still the warmest, a fact that was very clearly 

 ascertained, as a larger vessel than the " Medusa " was available, and soundings were 

 made well out in the North Channel, south of the Mull of Cantyre and across toward 

 the Galloway coast. The Channel was filled with water at the uniform temperature of 

 54°' 5, and from the Channel inward the temperature diminished. The coldest water in 

 the Arran Basin was a little under 48°, and occurred at the bottom off Skate Island. 

 The same temperature was reached at 15 fathoms in Loch Goil, where the bottom 

 temperature sank to 44°'3, and at 25 fathoms in Loch Fyne, where the bottom was 

 slightly under 44°. These deep lochs had thus kept their water more than 4° colder 

 than the open basins, and more than 10° colder than the open sea. On this occasion the 

 surface water was everywhere warmest, and the bottom water coldest, all indications of 

 an intermediate minimum having vanished from Loch Fyne. 



It should, of course, be remembered that practically all the observing stations were 

 midway between the coasts of the various natural regions examined, so that the effects of 

 local heating on a shallow shore were not observed. This effect is, however, considerable, 

 and in some places may materially raise the temperature of the shallow water, but the 

 broad inrush with every tide of the uniformly heated water from the Channel is unques- 

 tionably the most important factor in raising the temperature for the year. That its 



