6 DE. G. H. rOWLEE— BISCAYAN PLAjS^KTON : 



of H.M.S. ' Porcupine,' Station 38, 1869, position 47° 39' N., 11° 33' W., or about 

 150 miles W.N.W. of our usual position * ; and the curve of mean ocean temperatures t 

 has been placed alongside as III. 



This last curve, plotted, as Dr. Buchan said, "from the whole of the observations in 

 all latitudes for the different depths " recorded up to the date of his Report, may be 

 taken as the standard curve for ocean temperatures where unaffected by specific causes. 

 But curves I. and II., as compared with the regularity of III., show by a downward bow 

 that between 200 and 1000 fathoms the water is much warmer than it should be 

 according to the usually regular diminution of temperature. This is no doubt due 

 largely to the influence of the Gibraltar bottom current. At the Straits of Gibraltar 

 there is an upper inflow of colder water from Atlantic to Mediterranean, and a bottom 

 outflow of -warmer water from Mediterranean to Atlantic J : the influence of this warmer 

 water is vej-y conspicuous in the maps appended to Dr. Buchan's ' Challenger ' Report, 

 already cited, between 500 and 900 fathoms, as shown by a concentricity of the isobathy- 

 therms at these and intermediate depths with Gibraltar as a centre §. That the critical 

 points of the ' Porcupine ' curve are at higher horizons than those of the ' Research ' 

 curve, and that the curve as a whole is colder, is probably due to the more northerly 

 jiosition of the ' Porcupine ' station and its greater distance from Gibraltar. 



The letters in the sixth column under the head of "Weather" are taken from 

 Beaufort's scale, and are as follows : — 



B — blue sky. O = overcast. 



C = cloudy. R = raiu. 



M = mist. 



Under the heading of ** Light" in the log is recorded the number of seconds required 

 to turn the sensitive paper of Wynne's Exposure Meter to a standard tint. This method 

 of light-estimation was suggested to me by Mr. E. W. L. Holt: of course it records only 

 actinic values, not absolute light ; unfortuBately it is practically useless at dawn and 

 dusk, and is quite useless at night even -when there is a considerable amount of non- 

 actinic light. 



With regard to tlie occasional presence in a deep haul of isolated specimens of animals captured other- 

 wise only at higher horizons, it must be noted that wlule the nets were always washed out in fresh water 

 after a haul, there is always a possibility of a small animal adhering to the net and appearing in the 

 collecting-tin of a subsequent haul. Again, an animal from a previous haul may conceivably be left over 

 on a dipping-tube or in a killing-bottle, and so stray into a later haul, in the haste which is often 



* Wyville Thomson : Depths of the Sea, pp. 143 & 321. 

 t A. Buchan : ' Challenger ' Eeport on Oceanic Circulation, p. 9. 

 X ' Shearwater,' Proc. Eoj'. See. xx. p. 97. 



§ This explanation has also been accepted within certain limits by Dr. Gerhard Schott (' Valdivia ' Expedition, 

 Oceanograpbie, p. 18G). 



