52 THE DEPTHS OF THE SEA. [cHAP. II. 
of the Northern Hemisphere, much beyond 1,000 feet since the 
commencement of the Tertiary epoch. The tempcrature 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 aérated, 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. 
T 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 
tockall 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 
