676 DR HUGH ROBERT MILL ON THE 



Kvlcs of Bute, and Loch Fyne. The various trips made by the "Medusa" will be 

 described in detail when discussing the temperature of the water ; meantime a brief 

 reference to the twelve trips on which density observations were made is sufficient. 



In the Appendix, all the determinations of density are recorded in chronological order 

 for each of the natural divisions of the Area. The date, hour, and position are first 

 stated; then the depth in fathoms of the water, the depth from which the sample was 

 obtained with its temperature in situ, the state of the tide and of the weather. The 

 temperature (in centigrade degrees) of the water when its density was determined, the 

 density as found at that temperature and as calculated to 60° F. (15'56 C), and the 

 amount of chlorine in grammes per litre of water, calculated by Dittmar's table 

 ("calculated salinity"), conclude the summary. 



The Twelve Salinity Trips.- — The maximum, minimum, and average densities of 

 surface and bottom water for each station, together with the number of observations 

 from which they are deduced, are given in Table XVIII. , and serve as a rough approxi- 

 mation to the normal conditions prevailing during the period over which the observations 

 extended. They are also shown on the two maps, Plates V. and VI. 



The surface salinity appears to be subject to great fluctuations, the density ranging 

 from a minimum of r00114 to a maximum of 1 '02560, a range of 0'02446. In narrow 

 channels, and particularly at the head of lochs, the density was apt to be lowered by 

 spells of wet weather, or even by exceptionally heavy showers, in a manner that makes 

 the average for these stations quite uncertain. In the wider reaches of water the fluctua- 

 tions diminished as the sea was approached, and the density increased. Consideration of 

 surface density alone suggests the division of the Sea Area into two parts — the land- 

 locked lochs and narrow Dunoon Basin in the north, and the wide open Arran Basin and 

 Great Plateau in the south ; the two divisions may be termed the Landward and Seaward. 



The density of bottom water presents very remarkable constancy in all parts of the 

 area and at all depths. The extreme range is from 1 '02239 to 1 '02550, a range of 0'0031 1, 

 or little more than -^jih of the range of surface density. It is remarkable, also, that the 

 minimum occurs, both for extremes and means, in the Gareloch and not in any of the 

 regions of high rainfall and steep hill slopes. Excepting those in the Gareloch, which are 

 in many respects dominated in their character by the neighbourhood of the Estuary, none 

 of the stations show a close dependence of bottom salinity on distance from the sea or 

 amount of rainfall. To speak more accurately, the superficial freshening in no case 

 extends to a very great depth. The densities observed in each trip were written out 

 on separate maps of the area for surface and bottom, which are reproduced, to show the 

 maximum, mean, and minimum illustrating Table XVIII. The density results of each trip, 

 corrected to the standard temperature, were entered on two maps of the area, one showing 

 surface density, the other density at the bottom and intermediate depths. The wind, as 

 observed at each sounding, was marked by an arrow denoting its direction and strength, 

 and particulars of the weather for each day were entered in the margin. The changes in 

 the atmosphere over the area were taken from the Daily Weather Report of the Meteoro- 



