56 



NATURE 



\_May 19, 1887 



(3) Optical determinations of images by means of photo- 

 graphs suppHed by the Brothers Henry.— M. Struve. 



(4) The study of three or four stars nearly in a straight 

 line embracing the total angular distance of about 1°, and 

 photographed necessarily at the centre and at the corner 

 of a plate. —Paris, Algiers, Pulkowa, and Leyden. 



(5) Study of the deformations of films.— Algiers, Meu- 

 don, and Potsdam. 



(6) Study of curved plates from the triple point of view 

 of construction, means of covering with a film, and 

 measures. — Mr. Christie. 



(7) Study of absolute orientation — that is to say, the 

 mounting of the plates in the photographic telescope.— 

 The Cape and Paris. 



(8) Study of the measuring-instruments to be applied 

 for the future utilization of negatives. — This was postponed. 



(9) The study of formuhe for the preparation of plates 

 in accordance with the general rules laid down by the 

 Conference — Messrs. Abney and Eder. 



(10) Opinions of colours of stars on their photographic 

 magnitudes. — M. Duner. 



THE TEMPERATURE OF THE CLYDE 

 SEA-AREA.^ 



II. 



FROM the curves for each station, temperature sections 

 were constructed for every cruise, showing the position 

 of the isotherms with relation to a profile of the bottom 

 along certain lines. It is not easy to give an intelligible 

 description of the distribution of temperature without 

 reference to those diagrams ; but an attempt may be 

 made. The most important section runs from the 

 Channel, across the Plateau, up the Kilbrennan Sound 

 branch of the Arran Basin, through Inchmarnoch Water, 

 to the head of Loch Fyne. It is sufficient to recollect that 

 the Plateau is covered by about 25 fathoms of water, that 

 the depth increases on the inside up to 107 fathoms off 

 Skate Island, then diminishes rapidly to 15 fathoms at 

 Otter and Minard, and increases again to nearly 80 in Upper 

 Loch Fyne. The section is a little more than 90 miles 

 long. 



In April the whole section was filled with water between 

 4i°"3 and 44°. The water of the Channel, the Plateau, and 

 the surface layers (to 10 or 20 fathoms) was above 42°. 

 The average bottom temperature was 41 ^'3, except in the 

 Channel (42°), and in Upper Loch Fyne (4i'''9). The 

 June section shows marked surface heating to a depth of 

 about 5 fathoms. Water at 47° "5 filled the Channel, covered 

 the Plateau, and extended in a layer of about 5 fathoms 

 thick over the inner reaches. The great mass of water was 

 between 44°' 5 and 44°. In Upper Loch Fyne the re- 

 markable distribution of temperature, referred to when 

 discussing the curves for Strachur, was found to extend 

 from Minard to the head of the Loch, in the form of a 

 lenticular mass of water of temperature under 44°, with 

 warmer water above and below. The minimum tempera- 

 ture, 42', was found off Inveraray at a depth of 30 

 fathoms, and the gradient of temperature was much 

 steeper in the upper layers of the cold mass than in the 

 lower. No satisfactory explanation of the mode of 

 formation of this intermediate minimum of temperature 

 has yet been arrived at, and any suggestions as to its 

 origin would be received with interest. In August 

 the section shows that the cold mass remained in the 

 same position but with a rather higher temperature, and 

 of much smaller dimensions. As in previous months, 

 the warmest water was that nearest the Atlantic, which 

 had a temperature of over 53°. The great Arran Basin 

 presented a considerable range ; from 54° on the surface 

 to 50° at 20 fathoms, 48° at 30, 46° at 60, and 45^-3 on the 

 bottom. The September cruise showed a very similar 



' Continued from p. 39. 



State of matters, accompanied by a general rise of tempera- 

 ture and an increase in thickness of the warmer layers. 

 As in each previous month, the Channel was warmest 

 (54°*5 throughout), and the warm surface layer became 

 thinner and thinner until at Otter the surface temperature 

 was under 53°. The section clearly shows, what careful 

 experiments have proved, that the abrupt rise of the sea- 

 bottom, from off Skate Island at 107 fathoms to Otter at 

 15, is characterised by a rise of colder water from beneath 

 to the surface. The gradient at this place is 550 feet in ten 

 sea-miles, or i in 100 ; and perhaps vertical circulation is 

 set up as much by the sudden narrowing of the Channel, 

 as by its shoaling. A similar effect was observed at Row 

 Point in the Gareloch, and at the narrowest part of the 

 Kyles of Bute. In September the bottom temperature of 

 the Arran Basin was 47°'5, that of Upper Loch Fyne 

 44°"2 ; the intermediate minimum had disappeared from 

 the latter. November showed the influence of surface cool- 

 ing in a marked degree. The Channel and Plateau had 

 cooled down to 50°, and for the Arran Basin the average 

 surface temperature was 49^'5, that at the bottom 5i°'5. 

 This shows a great equalisation of temperature, and a 

 reversal of the summer conditions, the warmer water being 

 now below, the cooler on the surface. In Upper Loch 

 Fyne the temperature was 44° at surface and bottom, but 

 a maximum of a little over 50° was found at 1 5 fathoms. 

 Further cooling and greater equalisation of temperature 

 characterised December ; the Channel was warmest, at 

 48°"5 ; the whole Arran Basin varied from 46°*8 on the 

 surface to 47°"5 on the bottom ; and Loch Fyne maintained 

 its independent position by a quite new arrangement of 

 temperature-layers. On the days of our work there 

 (December 29 to 31) the whole upper part of the Loch 

 was covered with a sheet of frozen fresh water, the ice 

 being nearly half an inch thick in places. Three inches 

 beneath the ice the temperature was 36°, and a few feet 

 under, it was 44°. The maximum temperature of 47°"5 was 

 met at 20 fathoms ; and the warm layer of water was giving 

 out its heat to the superficial strata, being cooled by this 

 winter's cold, and to the lower mass which still retained 

 the cold of last winter, although the bottom temperature 

 had risen about half a degree since November. In 

 February it was impossible to observe in the Channel on 

 account of bad weather, but the water on the Plateau was 

 slightly colder (43'''4) than that in the Arran Basin (43°7 

 to 44"). There was little range of temperature, the surface 

 being in all cases, however, slightly colder. Throughout 

 the Arran Basin the temperature of the mass of water 

 was the same as in June : this may be held as pointing to 

 the end of April as the period of minimum. Loch Fyne 

 showed a steady rise of temperature as the depth in- 

 creased down to 45 fathoms, where the thermometer 

 registered 46°'5 ; from that point to the bottom there 

 was a fall to 4S°"8. 



Dividing the Clyde sea-area into three parts, each com- 

 prising regions of like physical configuration, the direction 

 of the annual march of temperature may be summed 

 up thus. 



Starting from the simple case of a minimum uniform 

 distribution, the Channel heats uniformly up to September, 

 and then cools uniformly ; the strong tidal currents, or 

 some other cause, keeping the water thoroughly mixed, 

 and equalising all heat transactions. 



The deep open basins, to which the tide has free 

 access, heat up most rapidly on the surface, and more 

 uniformly lower down ; the mass which heats uniformly 

 decreases until at the period of maximum there is an un- 

 broken fall of temperature from surface to bottom, and 

 a considerable range. Then, at the autumnal equinox, 

 the surface water begins to cool, while summer heat 

 is still travelling downwards : this leads to the typical 

 winter state — exactly complementary to the summer con- 

 dition — of a uniform gradient of temperature rising from 

 surface to bottom, but with a slight range. As winter goes 



