1870.] 



Deep-sea Researches. 



179 



of smoke, indicative of active changes in the molten depths beneath. Of 

 this activity, however, we had found no special indication in the Tempera- 

 ture-soundings taken nearest to the island. Whether the general prevalence 

 in the neighbourhood of Sicily of a Bottom-temperature averaging about 

 a degree above that of the Western part of the Mediterranean is due 

 to Subterranean heat, is a question which can only be determined by a 

 larger number of observations than we had the opportunity of making. 

 As we neared Stromboli, we were much struck with the height to which the 

 energetic industry of its inhabitants had carried the vine-cultivation all 

 round the cone, save on two slopes looking N.W. and S.E., over one or 

 other of which there is a continual discharge of volcanic dust and ashes. 

 Although no flames were visible during daylight, we could distinctly per- 

 ceive occasional flashes as night came on. — Our course was now laid straight 

 for Cape de Gat, which we passed on the 27th of September, arriving at 

 Gibraltar on the evening of the 28th. The only Scientific observations 

 which we had the opportunity of making during this part of our voyage 

 were confirmatory of those which we had made at the commencement of 

 our Mediterranean Cruise, as to the lower Temperature and inferior Den- 

 sity of the Surface-water, both which we attribute to the inflow from the 

 Atlantic. (See §§ 86, 92). 



61. Having taken in at Gibraltar as much coal as we could carry, we 

 left the harbour at 9 a.m. on the 30th Sept., and proceeded at once towards 

 the scene of our previous observations. We thought it worth while, how- 

 ever, to take a Sounding in our way towards this, near the 100-fathom line 

 (Station 63), for the sake of ascertaining the Temperature and Specific 

 Gravity of the bottom-water. The depth was found to be 181 fathoms, 

 showing that the slope from the shallow to the deep portion of the channel 

 is here very rapid. The bottom-temperature was 54°* 7, that of the surface 

 being 68°; and the Specific Gravity of the bottom-water was 1*0280, that 

 of the surface being 1 -027 1 • This bottom-water thus agreed closely in both 

 particulars with that of the deep mid-channel, as ascertained in our first 

 set of observations (§ 34), which were afterwards confirmed by our second. 

 We then steamed out to a point (Station 64) nearly identical with 

 that from which our previous investigations had been carried on ; and 

 commenced our work with a Temperature-sounding. The surface-tempe- 

 rature (65°* 6) proved to be here less by 2°*4 than it had been found to be 

 at Station 63 ; and this although it was taken an hour later in the forenoon, 

 when an increase might have been expected. It thus corresponded closely 

 with what had been previously found to be the average temperature of the 

 Strait in mid-channel, both during the first approach to Gibraltar from the 

 westwards (§ 30), and during our own experiments at the commencement 

 of the Mediterranean Cruise (§ 32) ; and the continuation of the like ob- 

 servations during the remainder of the day and ensuing night (§ 65) gave the 

 same remarkable result, the rationale of which will be considered hereafter 

 (§ 74). The depth was somewhat less than at the neighbouring Station 39, 



a 2 



