52 THE DEPTHS OF THE SEA. [CHAP. n. 



of the Northern Hemisphere, much beyond 1,000 feet since the 

 commencement of the Tertiary epoch. The temperature of deep 

 water seems to be constant for all latitudes at 39 ; so that an 

 immense area of the North Atlantic must have had its conditions 

 unaffected by ^Tertiary or Post-tertiary oscillations. 



One or two other questions of the highest scientific interest 

 are to be solved by the proposed investigations : 



1st. The effect of pressure upon animal life at great depths. 

 There is great misapprehension on this point. Probably a per- 

 fectly equal pressure to any amount would have little or no 

 effect. Air being highly compressible, and water compressible 

 only to a very slight degree, it is probable that under a pressure 

 of 200 atmospheres, water may be even more aerated, and in 

 that respect more capable of supporting life, than at the surface. 



2nd. The effect of the great diminution of the stimulus of 

 Light. From the condition of the Cave Fauna, this latter agent 

 probably affects only the development of colour and of the 

 organs of sight. 



I have little doubt that it is quite practicable, with a small 

 heavy dredge, and a couple of miles of stout Manilla rope, to 

 dredge at a depth of 1,000 fathoms. Such an undertaking 

 would, however, owing to the distance and the labour involved, 

 be quite beyond the reach of private enterprise. What I am 

 therefore anxious for is, that the Admiralty may be induced, 

 perhaps at the instance of the Council of the Royal Society, to 

 send a vessel (such as one of those which accompanied the Cable 

 Expedition to take soundings) to carry out the research. I 

 should be ready to go any time after July ; and if you would take 

 part in the investigation, I cannot but believe that it would give 

 good results. 



I would propose to start from Aberdeen, and to go first to the 

 Rockall fishing-banks, where the depth is moderate, and thence 

 north-westward, towards the coast of Greenland, rather to the 

 north of Cape Farewell. We should thus keep pretty nearly 

 along the isotherm of 39, shortly reaching 1,000 fathoms depth, 

 where, allowing 1,000 feet for oscillations in level, and 1,000 feet 

 for influence of surface-currents, summer heat, &c., we should 



