Prof. W. Thomson on the Depths of the Sea. 121 



Faroe Islands, who showed the greatest interest in the success 

 of our expedition, and on the verge of whose dominions it was 

 found. I dedicate the species to my distinguished colleague, 

 Dr. Carpenter. The mud was entirely filled with the delicate 

 siliceous root-fibres of the viti'cous sponges, binding it toge- 

 ther, and traversing it in all directions, like hairs in mortar. 

 This mud was actually alive ; it stuck together in lumps, as if 

 there were white of egg mixed with it ; and the glairy mass 

 proved, under the microscope, to be living sarcode. Prof. 

 Huxley regards this as a distinct creature, and calls it " Ba- 

 thybius." I think this requires confirmation. Every fibre 

 and spicule of each sponge has its own special sheath of sar- 

 code ; and the glairy matter in the mud may, I think, be 

 simply a sort of diffused mycelium of the different distinct 

 sponges. This view accords well, I believe, with the mode of 

 nutrition of the sponges. 



77ie Conditions of the Depths. — Pressure. — The conditions 

 which might be expected to affect animal life at great 

 depths in the ocean are pressure, temperature, and the ab- 

 sence of light, involving apparently the absence of vegetable 

 food. The conditions of pressure are certainly very pecu- 

 liar. A man at the depth of a mile would bear upon his body 

 a weight equal to about ten ordinary goods trains, engines 

 and all, loaded with pig iron. We are apt to forget, however, 

 that water is nearly incompressible, and that therefore the sea- 

 water at the depth of a mile has scarcely an appreciably greater 

 density than it has at the surface. At the depth of a mile, 

 under a pressure of 159 atmospheres, sea-water, according to 

 the formula given by Jamin, is compressed by the -j-^ of its 

 volume, and at twenty miles, supposing the law of the com- 

 pressibility of water to continue the same, by only -i- of its 

 volume ; that is to say, the volume at that depth will be still 

 f of the volume of the same weight of water at the surface. 

 Substances, also, permeated and uniformly supported within 

 and without by the water, are, so far as their physical condi- 

 tions, freedom of motion, &c., are concerned, in no way affected 

 by the pressure. We sometimes rise in the morning and find, 

 from a fall of an inch in the barometer, that we have been 

 gradually and quietly relieved during the night of half a ton 

 weight ; yet we feel it only by a slight lassitude, from its re- 

 quiring rather more muscular exertion to move our bodies in 

 the rarer medium. There is no reason to believe that water 

 contains less air at great depths than at the surface ; it is even 

 possible, owing to the great compressibility of air, that it may 

 contain more. As the increase in the density of the water at 

 the depths at which we dredged was scarcely perceptible, we 



