CL^DE SEA AREA. 23 



bottom was found to be 45° '7, corresponding closely with the condition of the North 

 Channel, the rise of 0°'3 in the interval between the two sets of observations being 

 insignificant. Loch Linnhe, fairly open to the sea, showed a temperature of 45° *5 on 

 the surface, a minimum of 44 0, 3 at 15 fathoms, and thence a rise to 44°"9 on the bottom 

 in 50 fathoms. Loch Etive, the most completely inclosed sea- water basin on the coast 

 of Scotland, showed in the deepest part surface water at 48°'4, a minimum of 44°*3 at 

 10 fathoms, and a rise to 47° "6 on the bottom, a condition very similar to that of Loch 

 Fyne at the same period of 1886. In Loch Morar, the deepest fresh- water lake in 

 Scotland (175 fathoms), the surface temperature averaged 43°'5, and all below 40 fathoms 

 was constant at 42°, while in Loch Ness nearly the whole mass of the water was at 

 41° "5. All the observations show clearly that the more completely a deep basin is cut 

 off from the sea, the more slowly is its water influenced by the advance of summer heat. 



Trip X., June 1887. — This trip, lasting from the 13th to the 18th, was thirty-eight 

 days later than the preceding one. The temperature of the air during June, as a whole, 

 was 3° above the average of the season for the Clyde Sea Area, while May had been 

 a month of average warmth. June 1887 was indeed the warmest on record, and the 

 great anticyclone which prevailed for the first half of the month is remembered by the 

 accident of including the days when the Queen's Jubilee was celebrated. Almost the 

 whole cruise was carried out in intensely hot, quite windless, cloudless, but slightly hazy 

 weather. On the 13th, however, there was a great deal of heavy rain, and on the 14th, 

 when Loch Goil, Dunoon Basin, and Loch Strivan were examined, there were frequent 

 drizzling showers. 



Solar radiation had here a perfect opportunity for showing its utmost power, and the 

 temperature of the surface water was naturally greatly raised. On the 16th, 17th, and 

 18th, the hottest days, the surface may be said to have stored, on the average, heat 

 enough to warm it by 2° per day. At no time in the summer of 1886 were such high 

 surface temperatures observed. 



Even in the Channel the surface water was warmer than that beneath, although the 

 range was, as it always is, less than in any other part of the Area where the depth is 

 equal. The range was from 52°*5 to 48°, the average being almost 2°*5 warmer than in 

 May. The Arran Basin, as a whole, had heated up about 4° throughout, and was 5° 

 warmer than in June 1886. This was particularly noticeable in the Western Branch, 

 where the temperature was considerably higher than in the equally deep parts of the 

 Eastern Branch. During the cruise the increase of temperature seemed to be due rather 

 to solar than to oceanic heating, and a prolonged series of hourly observations on the 

 Great Plateau furnished some important suggestions as to the mechanism of the interchange 

 of water by tidal currents. The great range between the temperature of surface and 

 bottom water on this occasion made it peculiarly opportune for an experiment to 

 determine the movement of the water. The deepest part of the Central Arran Basin 

 was filled with water everywhere over 46°, except at the upper end (next Loch Fyne), 

 where a mass of water at slightly lower temperature was found. This cold mass was 



