36 



BA RD WICKE'S SCIENCE-GOSSIP, 



more times greater. We feel it operating perpetually 

 on our own bodies, and yet can form no approxima- 

 tion to a rational idea of its mode of operation. 

 Theories of an electric fluid or fluids, and of electric 

 vibrations and undulations, have been attempted, and 

 some are satisfied therewith ; but the mystery of 

 gravitation defies even the imaginative inventors of 

 the universal all-pervading luminiferous "jelly." 



The Low Antarctic Barometer. — In a recent 

 number of "Nature," Mr. Murphy asks, "Why in 

 all the disquisitions on fluid equilibrium are the 

 constant low barometric pressures in the Antarctic 

 regions south of 60° neglected ?" and he proceeds to 

 explain them by the action of atmospheric currents. 



It certainly is a very curious fact that, as a ship 

 approaches the great icy Antarctic continent, the 

 barometer behaves precisely as though it were sailing 

 up hill by a very gradual incline, its mean height 

 diminishing as the ship comes nearer and nearer to 

 the precipice wall of ice which, so far as we know, 

 presents all around an impenetrable barrier to the 

 mountain mass which surrounds and possibly caps the 

 southern pole of the earth. 



I believe that the ship actually does sail up hill, 

 and that for a very simple physical reason. As 

 everybody knows, gravitation acts with a force vary- 

 ing inversely with the square of the distance between 

 the mutually acting bodies. Such a mass of lofty 

 mountain land and ice as that around the south pole 

 must pull at the ocean outside and be pulled thereby, 

 but the mountains cannot move towards the waters 

 of the ocean, while they, like Mahomet, are free to 

 go to the mountain. If they do so, the order of 

 their going will demonstrably be such that their 

 surface will form an inclined plane sloping upwards 

 towards the great protuberance. 



I am aware that certain mathematicians have esti- 

 mated the amount of displacement of the centre of 

 gravity of the earth due to such protuberant masses 

 of land, and have assumed that the only result as 

 regards ocean-level must be, that the ocean will 

 arrange itself around this altered centre. This, 

 although correct as regards the mean distribution of 

 the ocean, is fallacious as applied locally, as in 

 reference to the present question ; it is fallacious 

 because it only measures the force of gravitation of 

 the given mass of land, at its mean distance from the 

 mass of the ocean generally, i.e. from the centre of 

 gravity of the whole ocean ; but the oceanic matter 

 immediately surrounding the Antarctic continent is at 

 a shorter distance from this gravitating mass than is 

 the general mass of the ocean, and as we are dealing 

 with a mobile fluid, the scholastic formulae concerning 

 the movement of the whole mass <t)f a rigid body 

 with that of its centre of mass do not apply. If a 

 body were resting on a delicate spring balance, and a 

 great mass of lead were held just above it, the down- 

 ward gravitation of the body would be sensibly 



diminished if the mass of lead weighed many tons, 

 but the effect of the mass of lead upon the position 

 of the centre of gravity of the earth would be im- 

 measurably, I may say inconceivably, small. 



If I am right in the above, the mean height of the 

 barometer at the head of the Adriatic and near the 

 northernmost shore of the Gulf of Genoa and the 

 Riviera should be less than on the Egyptian boundary 

 of the Mediterranean ; it should also be lower on 

 the shores of Peru than on those of Brazil, as the 

 northern termination of the Mediterranean approaches 

 the foot of the Alps, and at Peru the ocean is 

 similarly near to the foot of the Andes, while at the 

 Brazilian coast, as on that of Egypt, there is a great 

 stretch of low land between the sea and the inland 

 mountain masses. The barometer should fall as we 

 sail towards the northern Mediterranean shores, and 

 as we approach from the west to the eastern coast of 

 South America. An experiinentum crucis may thus 

 be applied to this question. 



GOSSIP ABOUT FORAMINIFERA. 

 Part II. 

 By Edward II. Robertson. 



STILL another group, the Helicostegidae, presents 

 us with some of the most exquisitely beauti- 

 ful forms ever presented in shells. Commencing by 

 a small central chamber the subsequent chambers 

 are arranged in a spiral form, each cell added being 

 larger than that preceding it, so as to give the entire 

 shell the aspect of an Ammonite, or other spiral 

 shell. 



This group consists of the two families, Nauti- 



Fig. 20. — Peneroplis. 



Fig. 21. — Folystovzella crispa (after 

 Carpenter). 



loidre and Turbonoidre — the first including those in 

 which the successive whorls all lie in the same plane, 

 so that the shell is equilateral, like the Nautili and 

 Ammonites — whilst the second contains those in 

 which the spiral passes obliquely round an axis, so 

 that the shell becomes "inequilateral," like that of 

 a snail. Examples of these two methods of growth 

 are well shown in Figs. 21 and 23. 



