1870.] 



Deep-sea Researches. 



177 



proceed homewards without unnecessary delay, and as Capt. Calver was 

 desirous of avoiding, if possible, the necessity of going into port for coal 

 between Malta and Gibraltar, we found ourselves obliged to relinquish the 

 hope we had entertained of being able to resume our Dredging-explora- 

 tions in deep water along a different line on our return voyage. But, de- 

 siring to gain what addition we could to the information already acquired 

 respecting the Physical condition of the Mediterranean, we arranged so to 

 shape our course on leaving Malta as to enable us (1) to obtain a deep 

 Sounding in the Eastern basin, and (2) to ascertain the Bottom-tempera- 

 ture on an area of Volcanic activity. 



58. Quitting Valetta" Harbour at mid-day on September 20th, we 

 steered in a N.E. direction towards a point about 70 miles distant, at 

 which a depth of 1700 fathoms was marked on the Chart. This we 

 reached early the next morning (Station 60) ; and a Sounding being taken, 

 1 743 fathoms of line ran out. As this was the greatest depth we had 

 anywhere met with in the Mediterranean, and as the Basin in which the 

 Sounding was taken is cut off by the shallows between Sicily and Tunis 

 from all but superficial communication with the Western basin, we watched 

 the heaving in of the Sounding-apparatus and its accompaniments with no 

 little interest. The Thermometers recorded a Temperature of 56°, which 

 was one degree higher than that which we had met with in our two deepest 

 Soundings (1456 and 1508 fathoms) in the Western basin. The sample 

 of the bottom brought up in the tube of the Sounding-apparatus indicated 

 the prevalence of a yellowish clayey deposit so similar to that which had 

 elsewhere proved so disappointing, that we could not feel justified in pres- 

 sing Capt. Calver for the sacrifice of nearly a whole day, which would have 

 been required for a single cast of the Dredge at this depth. The speci- 

 men of Bottom-water brought up by our Water-bottle surprised us by its 

 very small excess of Density above the Surface-water ; the Specific Gravity 

 of the former being only 1*0283, whilst that of the latter was 1*0281 ; and 

 the proportion of Chlorine per 1000 being 21*08 in the former, whilst that 

 of the latter was 20*77. The Surface-water being here more dense than 

 the average, the Bottom-water was less dense — a result which a good deal 

 surprised us at the time, but which subsequent comparison with the densi- 

 ties of specimens taken from the greatest depths we had sounded in the 

 Western basin (§ 93) showed to be by no means exceptional ; and when 

 we came to reason out the mode in which surface-evaporation may be pre- 

 sumed to operate in augmenting the density of the water beneath, we found 

 it to be quite in accordance with a priori probability, that the deepest 

 water should show the least excess of density above the water at its sur- 

 face (§94). 



59. Having thus satisfied ourselves, so far as we could do by a single 

 set of observations, that the Physical conditions which we had found to 

 prevail in the Western basin of the Mediterranean present themselves also 

 in the Eastern, we steered for the Coast of Sicily ; and in a few hours 



VOL. XIX. Q 



