AfritS, 1880] 



NATURE 



543 



below the mean which will each be about double of the 

 numbers recorded above. 



10. Regarding the rainfall values as representing the 

 meteorological result of the sun's action, let us now com- 

 pare these with declination range values, which may be 

 taken to represent the sun's magnetic effect. Prof. Loomis 

 has compiled {American Journal of Science and Arts, 

 second series, vol. 1. p. 153) what seems to be a very good 

 table, exhibiting a set of yearly values of magnetic declina- 

 tion range, extending with slight breaks from 1777 to 

 1868. 



Let us take this table, and treat it precisely as we have 

 treated the rainfall, except that it does not seem neces- 

 sary to make any attempt at equalisation, such as that 

 made in Art. 8. 



We thus obtain the following result : — 



Proportional declination range inequality as exhibited by series of 

 8yrs. 9 yrs. 10 yrs. ir yrs. 12 yrs. 13 yrs. 14 yrs. 



5-39 IOO7 4-66 9-33 4-09 4-98 



Name of 

 station. 

 Prague, 



or re- I 

 duced to 1 ■* ■»' 

 Prague ) 

 Here we have unmistakable maxima corresponding to 

 ten and twelve years. The result is thus not unlike that 

 which we have derived from rainfall observations ; indeed 

 we could hardly expect a more perfect correspondence 

 between the two, bearing in mind the limited amount of 

 observations which we have for determining inequalities of 

 long periods. 



DEEP-SEA DREDGING AND LIFE IN THE 

 DEEP SEA • 



AS Dr. Carpenter explained in his lecture here some 

 short time ago, four-elevenths, or nearly three- 

 fourths of the surface of the earth is covered by sea. 

 The average depth of the ocean is, according to the 

 latest calculations of Mr. Otto Krummell, about 1,877 

 fathoms, or somewhat over two miles, very nearly the 

 distance from the Royal Institution to the top of Primrose 

 HilL If we try and project Primrose Hill directly under 

 our feet, keeping the distance the same, we shall form a 

 conception of the mean depth of the sea. The greatest 

 depth known to exist was discovered by the United States 

 ship Tuscarora near the Kurile Islands, in the North-east 

 Pacific. It is 4,655 fathoms, or about five miles and a 

 quarter. 



The highest mountain existing is of about the same 

 height as the deepest sea is deep. Mount Everest is 

 4,833 fathoms in height. So insignificant, however, is 

 the total volume of the land raised above sea-level in 

 proportion to the vast cavity occupied by the sea, that 

 were this cavity emptied of its water, the whole of the 

 land now above sea-level could be shovelled into it 

 twenty-two and a half times over before it would be filled 

 up to the present sea-level. 



Nevertheless the depth of the oceans, great as it is, is 

 as nothing in comparison with the vastness of their 

 extent of surface. As Mr. Croll has said, the oceans in 

 relation to their superficial area are as shallow as a sheet of 

 water 100 yards in diameter and only an inch in depth. 



The sides of the ocean-basins are not at all steep. They 

 are mostly so little inclined that an ordinary locomotive 

 engine could run up them in a straight line with ease. 

 Their inclination is usually not more than three or four 

 degrees or less. Around some oceanic islands the slope 

 is greater. The steepest slope known is, as Capt. Tizard 

 informs me, at Bermuda, where there is an inclination of 

 nearly twenty degrees from the edge of the reef to 2,000 

 fathoms. There are no such things as mountains and 

 valleys on the deep-sea bottom. Animals cannot slip 

 down against their will into the depths, but must move 



1 Friday Evening Lecture delivered at the Royal Institution on March 5, 

 by H. N. Moseley, F.R.S., Assistant Registrar of the University of London. 



deliberately into them, and travel a long journey to reach 

 them. 



The pressure exerted by the superincumbent water at 

 great depths is so great as to be almost beyond concep- 

 tion. It amounts roughly to a ton on the square inch for 

 every 1,000 fathoms of depth, about 166 times as much 

 as the pressure to which we are subjected at the present 

 moment. At the greatest depths the pressure is about 

 four tons and a half. Vast though this pressure is, it is, 

 however, only about one-eighth of that which Prof. Abel 

 and Capt. Noble have measured, as produced in their 

 experiments on gunpowder. The deep-sea animals, being 

 completely permeated by fluids, are probably no more 

 conscious of pressure acting upon them than we, and, so 

 long as they move slowly from one depth to another, are 

 most likely unaffected by the consequent changes of 

 pressure. 



With regard to the temperature of the deep-sea water, 

 the conditions which would affect animals are compara- 

 tively simple. Nearly all over the ocean the temperature 

 at 500 fathoms is as low as 40 F., and this is the case 

 even immediately under the equator in the Atlantic and 

 Pacific Oceans. Below 2,000 fathoms the temperature is 

 never more than a few degrees above freezing-point, ex- 

 cepting in the peculiar cases of land-locked seas, such as 

 the Sulu Sea. 



Fig. i.— Japanese dredge in action. 



At comparatively small depths in the sea it is almost 

 certainly entirely dark so far as sunlight is concerned. 

 Prof. Forel found that in the Lake of Geneva, even at a 

 depth of only 30 fathoms, photographic paper was entirely 

 unacted on after protracted exposure. We can hardly 

 believe that the red, green, or yellow rays can penetrate 

 sea-water much further than those to which ordinary pho- 

 tographic paper is sensitive. It may safely be assumed 

 that sunlight is entirely absent at a depth of 200 fathoms, 

 probably at a much less depth. We dredged blind Crus- 

 tacea at a depth of 120 fathoms, and a blind isopod is 

 found in the Lake of Geneva at a depth of about 55 

 fathoms. 



In depths of 500 fathoms almost everywhere, every- 

 where in over 1,000 fathoms, there must be an entire 

 absence of any currents in the water. Any movement 

 taking place in the water at that depth must be of a 

 molecular nature only, excessively^slow and quite imper- 

 ceptible to animals. 



Altogether the deep sea, cold, dark, and still, must b 

 about the slowest place to live in that can be imagined. 



I now turn to the consideration of deep-sea dredging. 



The dredge is an ancient contrivance of fishermen of a 

 very wide distribution. It is used in Japan, and the 

 accompanying amusing figure (Fig. 1) is taken from a 

 woodcut in a Japanese book on the principal land and 

 marine food products of Japan. In it a fisherman is 



