INTRODUCTION. 
8 
south and west coast of Ireland, where a depth of 
2400 fathoms was reached with successful results; 
and the third part extended over some portion of the 
survey of the previous year (between the coast of 
Scotland and the Faroe Islands). On the termination 
of this voyage (taking into account the time occupied 
and the extent of the investigations), the cruise of 
the Porcupine was considered to have done more to 
advance our knowledge of the physical condition of 
the ocean than had been achieved by any former 
expedition that ever left our shores. 
In 1870 the Porcupine was again engaged in the 
service of the Council of the Royal Society, and pro- 
ceeded at first in a south-westerly direction towards 
the farthest point to which the survey extended the 
year before, and afterwards to the coast of Portugal, 
and to Gibraltar, where a vast quantity of interesting 
and important data was obtained. In addition to 
the sounding and dredging, thermometric observa- 
tions were constantly taken, proving even more 
successful than those obtained during the previous 
voyages. The results showed unsuspected variations 
in the deep-sea temperature, the existence of a 
general oceanic circulation, and the presence of life 
at the greatest depths. The scientific and practical 
importance of the facts revealed by these short and 
imperfect inquiries was such as to render their con- 
tinuance a matter of national concern : so much so 
that the Council of the Royal Society brought before 
