536 



Dr. W. B. Carpenter on the 



[June 13, 



subject could not be fully elucidated without a far more prolonged and 

 systematic study of its phenomena than it was in our power to carry out. 



But, further, I had endeavoured to correlate the phenomena of the 

 Gibraltar Current with those of the Bosphorus and Dardanelles Currents, 

 and of the Baltic-Sound Current, under one general Physical Theory ; and 

 also to show that this Theory also applies to the doctrine of a General 

 Oceanic vertical Circulation sustained by difference of Temperature. For 

 whilst, in the case of Inland Seas, a disturbance alike of level and of equili- 

 brium between their water and that of the outside Ocean will be produced 

 either by excess of evaporation over the inflow of fresh water, or by an 

 excess of the inflow of fresh water over evaporation, the like disturbance 

 will be produced at the two extremes of each quadrant of the Earth along 

 which there is a free communication between the Polar and Equatorial 

 seas, by the opposite effects of Polar Cold and Equatorial Heat. 



This view has been strongly opposed, however, on the one hand by Cap- 

 tain Spratt, and on the other by Mr. James Croll. The former has not 

 merely affirmed* that this Physical Theory is altogether disproved, as 

 regards the Bosphorus and Dardanelles Currents, by his own observations, 

 but has called in question the validity of the evidence obtained by the in- 

 quiries of Capt. Calver and myself in regard to the Gibraltar Under- 

 current, and has expressed his disbelief in the Under- current Theory alto- 

 gether.— Mr. Croll, on the other hand, taking his stand upon what he re- 

 gards as a well-established datum in regard to the gradient necessary to 

 produce movement in water, considers that he has demonstrated the com- 

 plete inadequacy of Thermal agency to maintain the General Circulation I 

 advocate f. 



The objections of a Surveying Officer of Capt. Spratt's ability and expe- 

 rience could not but be entitled to great respect ; and I had therefore much 

 satisfaction in availing myself of the opportunity afforded me by the 

 Hydrographer, for cooperating with Capt. Nares in the re-investigation of 

 *he Gibraltar Currents, and for prosecuting such other scientific inquiries 

 during the voyage to Alexandria as circumstances might admit. 



The \ Shearwater 3 being specially fitted for the Surveying Service, only 

 such arrangements could be made for Scientific research as were consistent 

 with its requirements. And since it was not considered expedient to in- 

 clude deep Dredging in our programme, the following were the objects 

 which I proposed to myself, in addition to the investigation of the Gibraltar 

 Current :— 



I. To ascertain whether Serial Temperature-soundings off the Coast of 

 Portugal would justify the inference I had drawn, from the correlation of 

 the .B<?£r07/2-soundings taken in the previous year (Report for 1870, 

 §§ 79, 80 : Proc. Roy. Soc. vol. xix. p. 188), as to the existence of a 



* Proceedings of the Eoyal Society, June 15, 1871 (vol. xix.). 



t See his papers " On the Physical Cause of Ocean-currents" in the Philosophical 

 Magazine for Oct. 1870 and Oct, 1871. 



