October i6, 1890] 



NA TURE 



601 



jortant results. In a recent communication {Astronomische 

 Nachrichten, No. 2983), the orbits of Mimas and Enceladus, and 

 their relation to those of the other satellites, are considered. The 

 orbit of Mimas has an eccentricity of 0016, and an inclination 

 of 1° 26'. The retrograde movement of the nodes, is about 

 I "per day, and is accompanied by a direct movement of the 

 perisaturnium point, which is almost equal to it(- 365° and 

 + 371° per year). The comparison of the Pulkova observations 

 with those made at Washington {1882-86) indicates an accelera- 

 tion of the mean motion of Mimas, which corresponds to a re- 

 tardation in the mean movement of Tethys. Dr. Struve shows 

 that the changes in the elements and mean motions of the two 

 satellites may increase indefinitely, or vary between certain 

 limits. The latter explanation is proved to be the correct one, 

 and a discussion of the observations of Sir W. Herschel, Lassell, 

 Marth, Newcomb, Asaph Hall, &c., leads to the conclusion 

 that the conjunctions of Enceladus and Dione occur at the peri- 

 s.itumium of the former satellite or nearly so, whilst those of 

 Mimas and Tethys oscillate 45° about the point midway between 

 the ascending nodes of their orbits on iSaturn's equator, and 

 perform this iibration in about sixty-eight years. 



The masses of Dione and Tethys inferred by Dr. Struve from 

 the Iibration are respectively seven and eleven times smaller 

 than those deduced from photometric comparisons with Titan. 

 The result for Mimas is twenty-two times smaller than that fur- 

 nished by photometry. It appears necessary to admit, therefore, 

 that in the system of Saturn, as in that of Jupiter, either the 

 intrinsic brilliancy of the satellites increases, or their density 

 decreases, as the planet is approached. A knowledge of the 

 masses of the four above-named satellites, determined photo- 

 metrically and found by Dr. Struve, allows those of Enceladus 

 and Rhea to be estimated with some probability. The following 

 are the calculated and the hypothetical values in terms of the 

 mass of Saturn : Mimas, 1/11,500,000; Enceladus, 1/4,000,000; 

 Tethys, 1/767,000 ; Dione, 1/528,000; Rhea, 1/200,000; Titan, 

 1/4700. By adopting the above hypothetical values of the 

 masses of Enceladus and Rhea, the observed and calculated 

 values of the secular motions of the nodes and apses are found to 

 agree in a very satisfactory manner. The spheroidal constant of 

 Saturn has been determined as 0'0258, which differs consider- 

 ably from the value 0*0223 assumed in a previous paper {Astro- 

 nomische Nachrichten, No. 2946). This alteration obviates the 

 necessity of giving the ring-system a sensible mass in the 

 calculations. 



A New Comet (</i89o). — A faint comet was discovered by 

 Mr. E. E. Barnard, of the Lick Observatory, on the 6th inst. 

 It was then situated in Capricornus.^ 



ANTARCTIC EXPLORATION. 



T^HE following address, on "The Objects of Antarctic Ex- 

 -*■ ploration," was delivered at the annual meeting of the 

 Bankers' Institute of Australasia, at Melbourne, on Wednesday, 

 August 27, by Mr. G. S. Griffiths, P\G.S., F.R.G.S., His 

 Excellency the Earl of Hopetoun being in the chair. 



Mr. Griffiths said, — My experience, during the four years 

 which have elapsed since this project was first mooted in Mel- 

 bourne, is that any reference to the subject is sure to be met 

 with the query, Cui bono ? What good can it do ? What benefit 

 can come from it? What is the object to be served by such an 

 expedition? 



In setting myself to the task of answering these questions, let 

 me observe that it would indeed be strange if an unexplored 

 region, 8,000,000 square miles in area — twice the size of Europe 

 — and grouped around the axis of rotation and the magnetic 

 pole, could fail to yield to investigators some novel and valu- 

 able information. But when we notice that the circle is en- 

 girdled without by peculiar physical conditions which must be 

 correlated to special physical conditions within, speculation is 

 exchanged for a confident belief that an adequate reward must 

 await the skilled explorer. The expected additions to the 

 geography of the region are, of all the knowledge that is to 

 be sought for there, the least valuable. Where so many of the 

 physical features of the country — the hills, the valleys, and the 

 drainage lines — have been buried beneath the snow of ages, a 

 naked outline, a bare skeleton of a map, is the utmost that can 

 be delineated. Still, even such knowledge as this has a distinct 

 value, and as it can be acquired by the explorers as they proceed 

 about their more important researches, its relatively small value 



NO. 1094, VOL. 42] 



ought not to be admitted as a complete objection to any enter- 

 prise which has other objects of importance. Our present 

 acquaintance with the geography of the region is excessively 

 limited. Ross just viewed the coasts of Victoria Land, between 

 163° E, and 160° W. long. ; he trod its barren strand twice, 

 but on each occasion for a few minutes only. From the adjacent 

 gulf he measured the heights of its volcanoes, and from its 

 offing he sketched the walls of its icy barrier. Wilkes traced on 

 our map a shore-line from 97° E. to 167° E. long., and he 

 backed it up with a range of mountains, but he landed no- 

 where. Subsequently Ross sailed over the site assigned to part 

 of this land, and hove his lead 600 fathoms deep where Wilkes 

 had drawn a mountain. He tells us that the weather was so 

 very clear, that had high land been within 70 miles of that posi- 

 tion he must have seen it (" Ross's Voyage," 1278). More 

 recently Nares, in the Challenger, tested another part of Wilkes's 

 coast-line, and with a like result ; and these circumstances throw 

 doubts upon the value of his reported discoveries. D'Urville 

 subsequently followed a bold shore for a distance of about 300 

 miles from 136° E. to 142° E. long. ; whilst in 67° S. lat,, and 

 between 45" E. and 60° E. long., are Enderby's and Kemp's 

 lands. Again, there is land to the south of the Horn, which 

 trends from 45° to 75° S. lat.. These few discontinuous 

 coast-lines comprise all our scanty knowledge of the Antarctic 

 land. It will be seen from these facts that the principal geo- 

 graphical problem awaiting solution in these regions is the inter- 

 connection of these scattered shores. The question is, Do they 

 constitute parts of a continent, or are they, like the coasts of 

 Greenland, portions of an archipelago, smothered under an 

 overload of frozen snow, which conceals their insularity ? Ross 

 inclined to the latter view, and he believed that a wide channel 

 leading towards the Pole existed between North Cape and the 

 Balleny Islands (" Ross's Voyage," 1221). This view was also 

 held by the late Sir Wyville Thomson. A series of careful 

 observations upon the local currents might throw some light 

 upon these questions. Ross notes several such in his log. Off 

 Possession Island a current, running southward, took the ships 

 to windward [ibid., 1195). Off Coulman Island another drifted 

 them in the same direction, at the rate of eighteen miles a day 

 {ibid., 1204). A three-quarter knot northerly current was felt 

 off the barrier, and may have issued from beneath some part of 

 it. Such isolated observations are of little value, but they were 

 multiplied, and were the currents correlated with the winds 

 experienced, the information thus obtained might enable us 

 to detect the existence of straits, even where the channels 

 themselves are masked by ice-barriers. 



Finally, it is calculated that the centre of the polar ice-cap 

 must be three miles, and may be twelve miles, deep, and that, 

 the material of this ice mountain being viscous, its base must 

 spread out under the crushing pressure of the weight of its 

 centre. The extrusive movement thus set up is supposed to 

 thrust the ice cliffs off the land at the rate of a quarter of a mile 

 per annum. These are some of the geographical questions 

 which await settlement. 



In the geology of this region we have another subject replete 

 with interest. The lofty volcanoes of Victoria Land must pre- 

 sent peculiar features. Nowhere else do fire and frost divide 

 the sway so completely. Ross saw Erebus belching out lava 

 and ashes over the snow and ice which coated its flanks. This 

 circumstance leads us to speculate on the strata that would result 

 from the alternate fall of snow and ashes during long periods 

 and under a low temperature. Volcanoes are built up, as contra- 

 distinguished from other mountains, which result from eleva- 

 tion or erosion. They consist of debris piled round a vent. 

 Lava and ashes surround the crater in alternate layers. But in 

 this polar region the snowfall must be taken into account as 

 well as the ash deposit and the lava-flow. It may be thought 

 that any volcanic ejecta would speedily melt the snow upon 

 which they fell, but this does not by any means necessarily follow. 

 Volcanic ash, the most widespread and most abundant material 

 ejected, falls comparatively cold, cakes, and then forms one of 

 the most effective non-conductors known. When such a layer, 

 a few inches thick, is spread over snow, even molten lava may 

 flow over it without melting the snow beneath. This may seem 

 to be incredible, but it has been observed to occur. In 1828, 

 Lyell saw on the flanks of Etna a glacier sealed up under a 

 crust of lava. Now, the Antarctic is the region of thick-ribbed 

 ice. All exposed surfaces are quickly covered with snow. Snow- 

 falls, fish-falls, and lava-flows must have been heaping them- 

 selves up around the craters during unknown ages. What has- 



