If 



NATURE 



\_Nov. 21, 1889 



Is Greenland our Arctic Ice Cap ? 



The result of Dr. Nansen's journey across Greenland, estab- 

 lishing, as it practically does, that this Arctic continent is covered 

 by a huge ice cap, promises to be a matter of some interest in 

 several ways. 



Among other things it may possibly yield a clue as to the 

 cause of the south polar cap of Mars being so very excentrically 

 placed. 



Since the time of the elder Herschel this has been a subject of 

 speculation, and various ingenious suggestions have been put 

 forward by astronomers to account for the presumed anomaly. 



Webb, in his "Celestial Objects," p. 147, tells us that 

 Herschel found that the caps were not opposite each other ; 

 and says himself that "one would expect that they might have 

 been diametrically opposite." 



" Madler and Secchi found the north zone concentric with the 

 axis, but the south considerably excentric " ; and "it has been 

 suggested by Beer and Madler that the poles of cold may not 

 coincide with the poles of rotation." 



Later on, at p. 148, he tells us that " Secchi found the appear- 

 ances at the poles irreconcilable with the idea of circular caps, 

 and was forced to adopt the supposition of complicated and 

 lobate forms. Schiaparelli alludes to the possibility of a mass of 

 floating ice." 



Apparently it was taken for granted that the ice or snow caps 

 of Mars, should not only be truly circular in form, but centrally 

 placed over the axis of rotation, like the cloud caps of Jupiter and 

 Saturn. 



But it seems to me that Dr. Nansen's journey will go a long 

 way towards solving this problem, by demonstrating that Green- 

 land is practically one of our two polar ice caps. On our South 

 Pole we have one, more or less centrally placed over the axis of 

 rotation, and which certainly does not float about, having two 

 large active volcanoes on it. It corresponds fairly well to the 

 northern pole of Mars. But on our North Pole — as far as we can 

 see — there is no large permanent ice cap, and in its place we 

 have an irregular, extensive polar basin. 



Roughly speaking, we may say that the character of the Arctic 

 and Antarctic ice bears this out, for in the south we see the im- 

 mense flat-topped bergs of 2000 feet thickness, and several miles 

 long, which are obviously portions of the southern ice cap broken 

 adrift. In the north we see a preponderance of floe, or thin 

 field-ice, a few flat-topped bergs near Franz Joseph Land 

 (Young), and the angular bergs of the Atlantic, mainly from 

 West Greenland (Greely). 



If our Arctic basin is deep and has few islands in it, it stands 

 to reason that a permanant ice cap could not form, or become 

 anchored, there ; the floe would be perpetually broken up by 

 storms and tides, carried away, and melted. A floating ice cap 

 would be impossible. The presence of a polar continent — even 

 excentrically placed — would seem to be necessary, as in the 

 case of Greenland. This would indicate the solution for the 

 supposed anomaly, re the position, of the south polar cap of 

 Mars, and for the lobate appearances remarked by Secchi 

 in 1858. 



If the foregoing remarks are at all likely to be correct. Dr. 

 Nansen's journey may have quite unexpectedly solved for us an 

 interesting astronomical problem, and thereby afforded another 

 clue to the condition of Mars, a proof almost of partial 

 glaciation. 



I believe that M. Fizeau regards the so-called "canals" as 

 evidence of the " movement and rupture " of a glacial crust. 



But if this crust is formed on, and attached to, any extensive 

 land surface (such as Greenland, say), it is not easy to account 

 for such enormous ruptures, and the lateral movement. 



If the canals are looked on as huge lanes of open water in a 

 floating ice-pack, they would vaiy in size and form almost daily. 

 Sibsagar, Assam, India, September 25. S. E. Peal. 



Globular and other Forms of Lightning. 



Mr. a. T. Hare's account in Nature, vol. xl. p. 415, of 

 a flash of globular lightning seems to illustrate so well the 

 explanation which I gave, many years ago, of the formation of 

 fire-ball lightning, that the following extract from my pamphlet 

 "On Atmospheric Electricity" (London, Hardwicke, Piccadilly, 

 1863) and the remarks which I have appended to it, may per- 

 haps not be without interest at the present time. The pamphlet 



is not now on sale. The quotation is from pp. 45-46 ; I omit 

 a few references : — 



"A slip of tin-foil was formed into a hollow cylinder, and 

 thrust tightly into one end of a glass tube which was about i\ 

 inch in external diameter, and the glass was not very thick. 

 A brass ball was fixed to the end of the glass tube, and the tin- 

 foil extended from the ball to the distance of about \2\ inches 

 from it, and all the tin-foil was inside the glass tube. The 

 remainder of the glass tube served for an insulating support to 

 the part which held the tin-foil. On electrifying the ball, the 

 electricity is conveyed by the tin-foil to the inside surface of the 

 lined part of the glass tube ; and at the same moment the out- 

 side of this part of the tube is electrified inductively, and with 

 the same sort of electricity as that with which the interior of the 

 tube is charged. The part of the tube which held the tin-foil 

 was supported horizontally. There was also a copper hook 

 which could be set on any part of the outside of the lined portion 

 of the glass tube. 



"The copper hook was set at a distance of l\ inches from the 

 brass ball on the end of the tube, and was connected with the 

 outside of a Leyden-jar which was charged so as to be nearly 

 able to give a spark \ inch long between two other brass balls 

 each of which was i^ inch in diameter. The knob of the jar 

 was next brought to the ball on the end of the glass tube ; the 

 discharge readily passed over the 7^ inches of the electrified 

 outer surface of the glass tube. Sometimes the spark could 

 pass when the hook was at 8| inches from the ball. When 

 the hook was placed at a distance of \z% inches from the ball, 

 the spark passed between the ball and the hook with a much 

 lower charge in the jar than was necessary to produce a spark 

 f inch long between the pair of balls before mentioned. 



" These experiments show that the length of an ordinary 

 electric spark, can be much increased > by causing the spark to 

 pass over an electrified surface. Instances of this are seen in the 

 spontaneous discharge of Leyden-jars, and in the long sparks 

 which flash over the revolving glass of the electrical machine. 



" Let a ball be attached to the prime conductor of the elec- 

 trical machine so that the ball may give electrical brushes to the 

 air. Much longer sparks may be drawn from the ball along the 

 path of the brushes than from the other parts of the prime con- 

 ductor. The brush discharge electrifies the air in the neigh- 

 bourhood of the ball, and the spark is longer because it passes 

 near to, or through, a mass of previously charged particles. 



" It is well known that atmospheric electricity not unfre- 

 quently forms an electric fire-ball which moves but slowly, and 

 which, on striking an object, explodes and produces all the usual 

 effects of a flash of lightning. Sir William Harris writes : — 

 ' Now, it is not improbable that, in many cases in which distinct 

 balls of fire of sensible duration have been perceived, the appear- 

 ance has resulted from the species of brush or glow discharge 

 already described, and which may often precede the main 

 shock.' And Dr. Noad says of the electrical fire-ball that ' it 

 is no doubt always attended by a diff"usely-luminous track ; this 

 may, however, be completely eclipsed in the mind of the ob- 

 server by the great concentration and density of the discharge in 

 the points immediately through which it continues to force its 

 way.' A more perfect explanation can, as I suppose, be given 

 by the aid of the experiments of this chapter. 



" A thunder-cloud may produce both the electric glow and the 

 electric brush, at the end of one of its cloudy branches. And since 

 electricity passes freely along a charged surface, therefore the 

 glowing discharge by electrifying the air in front of the aerial 

 conductor, adds continually to the length of the conducting 

 column, and so the electrical fire-ball advances. Little drops of 

 water, or any other conductive matter which the column finds 

 in its course, must facilitate the transmission of the electricity 

 to the fire-ball ; and without doubt, too, the electricity of the 

 column continues to spread laterally, and so it increases the con- 

 ductive capacity of the column. The electricicity travels through 

 the electrified column as a series of luminous disruptive dis- 

 charges ; but the light is brightest at the head, because there the 

 diameter of the column is least, and the discharge is most closely 

 packed ; and because there the air is unelectrified, and conse- 

 quently opposes so great resistance to the passage of the elec- 

 tricity. As soon as the fiie-ball has arrived at a conducting 

 mass on the earth, the aerial conductor has been completed, and 

 a flash of lightning may instantly follow along the path of the 

 fire-ball." 



Since the Leyden-jar, with a charge somewhat less than that 

 required to give a spark \ inch long between the li-inch brass 



