CHAPTER IX
MAGNETISM, AURORA, AND TIDES
Almost every important recent Polar expedition that has set out for work extending over twelve months, has laid itself out to make a study of the magnetic conditions either of the Arctic or Antarctic Regions. The two polar ships that have been specially equipped recently for taking magnetic observations on board were the Discovery and the Gauss, upon which large sums of money were spent to secure a special area of the ship free of local magnetic influences. No other polar ships have ever been equipped so particularly in this direction, though many others, notably the Erebus and Terror in the Antarctic Regions, did a considerable amount of magnetic work. Recently the Carnegie Institution at Washington have fitted out a magnificently equipped non-magnetic sailing ship, the Carnegie, which is carrying out work of the highest importance in the form of a magnetic survey of the seas of the world. Unfortunately this fine ship does not appear to be fitted out for navigation in ice, consequently this important survey must remain incomplete until some munificent millionaire resolves similarly to equip and endow a ship to complete the work by carrying out a systematic magnetic survey of the seas of the Arctic and Antarctic Regions.
But although so little has been done with regard to magnetism in polar seas, yet a very considerable amount has been done in polar lands. All the recent Antarctic expeditions carried out magnetic observations on land. The station set up by the Scottish Expedition in the South Orkneys has now conducted observations there continuously during the last eight years, thanks to the energy of Mr. W. G. Davis and the Government of the Argentine Republic. It is of interest to note that Sir James Ross, serving under his uncle Sir John Ross, was the first to take magnetic observations at the North Magnetic Pole, in 1831, and that Mr. D. Mawson, serving under Sir Ernest Shackleton, was the first to take magnetic observations at the South Magnetic Pole, in 1909. Though it is a matter of satisfaction to have the British flag hoisted in both magnetic poles of the globe, the intrinsic value of the observations taken there is not very great from a scientific standpoint, as Mawson himself points out, since they are only single isolated observations, but the good series of observations that Mawson has taken in the neighbourhood of the South Magnetic Pole, as well as those of Bernacchi, are of the highest possible value. Further observations in circles round about the approximate point of each magnetic pole would add very much to our knowledge of terrestrial magnetism.
Terrestrial magnetism is altogether a most intricate and difficult science, but it is perfectly obvious that one very great use of an intimate study of this subject is for purposes of navigation. In the days of sailing ships, the finest course that was laid till recent years was to a quarter of a point or nearly three degrees of the circle, nowadays no steamer of any importance steers a wider course than one degree. The Mauretania, for instance, Captain W. T. Turner tells me, "is steered and the course set to degrees." In one instance, at least, I know of the captain of one liner insisting on an accuracy of a quarter of a degree, the helmsman keeping the course to that amount of accuracy by means of a magnifying glass placed over the compass card. With fine courses, such as those that are necessary for the high speeds attained, with the great value of these modern leviathans, with valuable cargoes, and with a thousand or more human beings on board, it will be seen how important an accurate knowledge of terrestrial magnetism is.
There is no more striking or wonderful phenomenon in the Polar Regions than the aurora—Aurora Borealis in the north and Aurora Australis in the south. Any one who has wintered in the Arctic Regions has had good opportunity of witnessing the aurora in all its splendour. It is not unknown in Europe during the dark winter nights, having been recorded as far south even as Italy, Spain and Portugal. It cannot, however, be regarded as a common phenomenon in southern Europe, and indeed does not become frequent until one reaches the latitude of the north of Scotland.
"Loomis and Fritz," says the late Dr. Alexander Buchan, "have severally investigated the geographical distribution of the Aurora Borealis. The region of greatest auroral action is an oval-shaped zone surrounding the North Pole, whose central line, i.e. the more or less elliptical line halfway between the northern and southern extension of the zone, crosses the meridian of Washington in latitude 56° and the meridian of St. Petersburg in latitude 71°. It follows from this that auroræ are more frequent in North America than in the same latitudes in Europe. Loomis points out that this auroral zone bears considerable resemblance to a magnetic parallel or line everywhere perpendicular to a magnetic meridian."
"It is a fact of the greatest significance that, as regards geographical distribution, auroræ and thunderstorms are complementary, auroræ being not more characteristically of polar than thunderstorms are of tropical origin; whereas thunderstorms may be regarded as completely dissociated from magnetic associations, and their periodicities are restricted to diurnal and annual variations" ("Aurora Borealis or Northern Lights," Chambers' Encyclopedia, 1901).
At Ben Nevis Observatory auroras have been frequently recorded, and indeed on many occasions there are very remarkable displays to be seen from the summit of that mountain. The most frequent form is a low arch of more or less elliptical form, rising not many degrees above the horizon to the north-west. On more than one occasion I have seen perfect coronas with their waving bands of streamers darting out from the zenith at times almost to the horizon. All the displays that I have seen on Ben Nevis had the streamers lighted with that lurid pale yellowish-green colour that every Arctic explorer is familiar with, but on one occasion at least there were mingled with it flashes of rosy red, which passed along the living bands. In Franz Josef Land during the winter of 1896–97 there were specially fine displays of auroras, and frequent observations were made upon them, by various members of the expedition. Armitage, who conducted the magnetic work, found that the declination of the magnetic needle was disturbed by the presence of the aurora.
This interesting observation was by no means a new one, for in 1741 Celsius and Hiorter noted for the first time the simultaneity of the Aurora Borealis and the disturbances in magnetic declination. From 1741 to 1747 Hiorter recorded forty-six examples of this coincidence. At the suggestion of Celsius, Graham made corresponding observations in Britain, and it was found that the magnetic disturbances were synchronous on the same days in Sweden and Britain. These observations were followed up by Wargentin, Canton and Wilcke. Wilcke found that every time, or almost every time, there was a magnetic disturbance, that disturbance was accompanied by a display of Aurora Borealis; but the inverse was not found to be the case, that is to say, the Aurora Borealis might be observed without any disturbance of magnetic declination accompanying it. Between 1771 and 1774 Wilcke proved that the inclination of the needle was also affected and that the centre of the corona corresponded with the magnetic zenith.
Humboldt, in 1806, discovered that there was a relationship between the magnetic force and the Aurora Borealis. In 1834 the Magnetic Association founded by Gauss and Weber, and the stations organised by Sabine in many British colonies, multiplied examples of the relationship of auroræ and disturbances in the three elements of terrestrial magnetism, viz., declination, inclination, and intensity. These observations showed at the same time the extreme complexity of the subject. Some of the most interesting observations that have been made actually within the Polar Regions are those of Weyprecht, in the Tegetthof expedition to Franz Josef Land. Weyprecht noted that during these disturbances the declination needle was displaced towards the east, and that the horizontal intensity was diminished and the vertical intensity increased. Curiously, Parry near Melville Island and Port Bowen, not far from the Magnetic Pole, never recorded any relationship between displays of the Aurora Borealis and the movements of the magnetic needle. Ross, on the other hand, obtained opposite results in the same region, while M'Clintock and Kane's observations tend to confirm those of Parry. No relationship between these phenomena appears to have been recorded by the British expedition of 1875–76.
But Armitage says, in Franz Josef Land, "I could not avoid noticing the vagaries of the magnet, and attributing them to the frequent brilliant displays of auroral light which held us entranced during our stay in the ice-bound North. More especially did the magnet appear to be affected when the aurora, rising in massive, thick arches from the eastward, and sending up streamers of beautifully coloured light, passed rapidly across our zenith and disappeared to the westward. . . . The magnet would oscillate wildly from side to side, or sometimes sheer rapidly to one side only, then as suddenly behave in a steady and normal manner." Armitage also noted that the most brilliant air effects took place during a "furious gale" or a "dead calm."
Buchan has pointed out that "Lemström has shown, by observations and experiments he made at Sodankylä, that auroræ are due to currents of positive electricity illuminating the atmosphere in their passage to the earth. Luminous appearances accompanied the setting in of a current towards the earth from the network of insulated wires with which he overspread the top of Mount Oratunturi, and this light was clearly auroral, giving the hitherto enigmatical citron line of Augström, which is the invariable constituent of aurora radiations. Other faint and indistinct lines are enumerated as present, and Lemström is of opinion that there is a tolerable agreement between some of these and the lines in the laboratory spectrum of rarefied air, but the whole subject demands further investigation."
Various theories have been advanced to account for the occurrence of auroræ, and among others has been suggested that the phenomena is due to the presence of cosmic dust. This, however, does not appear to be at all likely: in all probability it is a purely electric magnetic phenomena. It seems likely that the phenomena occurs in other planets than our own: it is known that the obscure hemisphere of Venus appears to be often illuminated, and Winnecke says that this illumination is of a greyish violet colour—in this connection it is interesting to note that these illuminations in Venus were especially observed during the years 1721, 1726, 1759, 1796, 1806, 1825, 1865 and 1871, and that 1726, 1759, 1865, and above all 1871, were notable years for the display of the Aurora Borealis.
One of the earliest theories put forward was in the middle of the thirteenth century in an old Norwegian book called the King's Mirror, where one quaintly reads, "Some people think that this light is a reflection of the fires which surround the seas to the north and to the south; others say that it is a reflection of the sun when it is below the horizon; I think, however, that it is produced by the ice which radiates during the night the light that it has absorbed during the day" (Les Aurores Polaires, by A. Angot, 1895).
The displays of aurora in Franz Josef Land during the winter 1896–97 were particularly brilliant and frequent. The usual display consisted of a series of waving ribbon bands like muslin frills, composed of vertical streamers in continuous motion, the streamers appearing to pass with varying intensity from end to end of these flowing ribbons covering almost every point of the sky; every now and then the streamers would shoot out to an immense length downwards towards the earth and far upwards towards the zenith, forming a corona from which all the rays that filled the whole sky appeared to originate. This coronal appearance is probably perspective effect, due to the enormous length of the shimmering rays. The general display of colour was exactly the same as has been described at Ben Nevis Observatory, but much more intense, and culminating during the most brilliant periods with flashes of emerald green, brilliant crimson, and delicate violet hues, which pass from end to end of the never-ending, ever-intertwining ribbons. It can scarcely be compared with any familiar object unless it be to an imaginary ballet in the sky, where the figures are in extraordinarily rapid motion, passing in continuous procession, one line of dancers mingling with another, and a series of flashlights of different colours passing rapidly across the tinselly muslin drapery. The whole effect is weirdly beautiful, and has long been known in the Highlands of Scotland by the very fitting name of the "Merry Dancers."
It may be of interest to give one or two quotations from my diary when I was wintering in Franz Josef Land. On January 1, 1897, my log runs, "Auroras have been fairly frequent; I have not seen one like those I have seen at Ben Nevis in Scotland, where you get the distinctive arch or series of arches with streamers flowing along upward and darkness under the arch. One arch I have seen here, but not a perfect one, about six weeks ago. Within the dark area was the crescent moon to the southward. The arch at each end was flattened, or rather it was a semi-ellipse or such-like. No streamers flowed from the arch, it was rather a band than an arch. Here (except where there are simple bands, not the most general form) the streamers shoot downwards from the zenith and dance about in spiral waving arrangement. Sometimes there is a break between the lower ends of the streamers and the zenith, but still the streamers seem to continue as if in a line from the zenith or towards it." Writing on January 6, 1897, I say of the 3rd of January, "although there was fog and slight snow, there was a brilliant aurora quite lighting up the scene. A very distinct shadow was thrown under my hand when placed 5 or 6 inches above the ground (snow). I have often seen auroras casting shadows here and lighting up the cliffs brilliantly. On the evening of the 3rd, at times streamers came playing brilliantly through the fog from the zenith, gambolling round and looking like brilliantly illuminated falling snow. The general impression I have received is that bands and collections of streamers have a more usual distribution across the zenith from east to west, but their directions are very varied."
On the 24th of January, 1897, at 9 p.m., I record "a band of aurora to-night from west-south-west to east, throwing up streamers toward the zenith. Curious appearance at east end being broken up like a very perfect type of fine cirro-cumulus cloud, looking as if illuminated by brilliant sun to the south-south-west; the band was broad and appeared to be crossing some cirrus clouds, and showed a mottled appearance. Here the dark portions were obviously due to cloud and aurora behind them, but to the eastward the cirro-cumulus sunlit appearance was, I believe, purely auroral. Wilton saw this, to whom I pointed it out."
"I have, on moonlight nights, seen aurora and cirro-stratus—one running into the other imperceptibly, not being able to tell with absolute certainty whether it were cirro-stratus with aurora or aurora alone."
Many other quotations regarding aurora I have observed could be made, but these three sum up many characteristics not only for Franz Josef Land but for other parts of the Polar Regions—north and south.
It has been said that the aurora is accompanied by a crackling sound, but although carefully attentive for such a sound none of us ever heard it in Franz Josef Land, the opinion at the time being that such crackling sounds might be due to the crackling of ice and snow during an aurora, when there was also intense frost—the sound being caused by the frost, and not by the aurora.
So much for the Aurora Borealis with which every one who has wintered in the far north is so thoroughly familiar. There is a different story to be told in the south, where, during the two cruises and the wintering of the Scotia not a single Aurora Australis was seen. Neither do the Swedish and French expeditions appear to have seen any definite displays of the aurora. Dr. Nordenskjold writes to me, saying, "We never did see any display of aurora at all during the time of our stay in the South, though looking always for such." Dr. Charcot says, "During both my expeditions, 1904 and 1909, we had once in 1904 and once in 1909 something resembling an aurora, extremely faint, and uncertain if they had not been accompanied by magnetic perturbations. We had glares of pale green, which might have been attributed to auroras, but I really do not think they were. The two auroras showed themselves in the S.E." On the other hand, the English expedition in MacMurdo Sound had frequent displays during the whole time the Discovery wintered. "On the whole the displays, although very frequent, were extremely poor, and were generally in the following forms:" (1) Faint lights with no defined forms. (2) Luminous patches, which frequently presented the appearance of clouds. (3) Incomplete arcs, or segments of arcs, of which the brilliance was not uniform nor the border regular. From these arcs rays would frequently shoot up intermittently. (4) Rays, or vertical shafts, separated from each other at a greater or less distance, frequently described as streamers. (5) In one or two exceptional cases irregular bands, formed of rays or vertical shafts, pressed close together and forming "draped auroræ."
"The faint lines and luminous patches were of the most varied dimensions, sometimes very small and at other times occupying almost the whole of the eastern (geographical) sky; their brilliancy was rarely much more intense than that of stars of the 4th magnitude, or even the Milky Way. They formed, as it were, a white veil over the sky through which stars of small magnitude were plainly visible. A clearly defined arc formed of a homogeneous luminous mass touching the horizon at both extremities, was rarely seen."
"Spectroscopic observations of the auroræ were not successful, due, apparently, to the weak intensity of the light."
"The observations of atmospheric electricity taken during the displays reveal no special effect referable to the aurora."
"An examination of the journal shows that the largest number of auroræ occur during mid-winter months, June and July."
Although, on the whole, the displays of the aurora seen by the Discovery were extremely poor, and mostly straw colour, faint pink and green only having been observed on a very few occasions, Ross, in the same longitudes, but farther to north, had brilliant displays on more than one occasion in February and March 1841.
It is very interesting to get a comparison of the Aurora Australis and Aurora Borealis by one who has seen brilliant displays of both, and in this connection Captain A. B. Armitage writes to me, saying, "The Aurora Australis could not hold a candle to the Aurora Borealis. I never saw colour so brilliant in the South as in the North; never did light emanate from the auroral arches hovering over Victoria Land cast a shadow such as did the flickering streamers and coruscating coronæ of Franz Josef Land. In the North, too, I have seen the auroral light between me and a cliff 500 feet high and only 100 yards distant. I have seen stars of the third magnitude eclipsed by it and the moon's light pale before it; not so in the desolate South."
On March 23rd, Ross says, "Late in the evening we crossed the line of no variation in latitude 62° 0′ S. and longitude 135° 50′ E. At 7.20 p.m. observed a bright arch of the Aurora Australis west-north-west and east-south-east extending across the zenith, of a yellow colour, its edges tinged with a purple line. . . . The lustre of the larger stars was much dimmed as it passed over them, but they could be distinctly seen through it; some of the smaller stars were totally obscured by the brighter and denser portions of the aurora; this splendid display was, as usual, followed by a fall of snow."
On March 26th, Ross says, "The aurora again afforded us a considerable light at night, in the absence of the moon"; and again, "On the evening of the 27th we witnessed a most brilliant exhibition of Aurora Australis. . . . Before 10 o'clock bright streamers darted upwards from the cloud to the zenith, forming coronæ, and exhibiting bright flashes of all the prismatic colours, green and red being the more frequent and conspicuous; this aurora had much motion, darting and quivering about the sky in rapid flights, and in every direction."
Rather in contradiction to Buchan's statement, Ross records, on the 28th of March, that "at 10 p.m. a single flash of forked lightning was seen in the north-north-east and at the same time an arch of aurora extended across the zenith from the horizon west-north-west and east-south-east; it was then blowing a strong north-westerly gale." Again, "The Aurora appeared in great brilliancy during the night of the 30th." Buchan's statement is, however, generally speaking correct, this being another of those cases illustrating how impossible it is to draw hard-and-fast lines in nature.
The study of tides is an important part of Polar exploration, and their study in Antarctic Regions more generally useful than in the Arctic Regions, for in the Great Southern Ocean lie the original tides of the world.
"The Scotia results," says Sir George Darwin, "are very valuable as relating to the only ocean uninterrupted by land throughout the whole circumference of the globe," and they acquire much importance when considered in connection with the very abnormal results obtained by the Discovery.
At Scotia Bay "the tides seem to be normal for a place in the Southern Ocean."
One of the most remarkable results of tidal observations taken in the Antarctic Regions, is the belief expressed by Sir George Darwin (Proc. Royal Soc., A vol. 84, 1910) that those observations taken during Shackleton's expedition reveal a sea-seiche. These sea-seiches are known to exist in different parts of the world, and have been specially observed in many Japanese bays; but Sir George Darwin points out that in none of the examples given "has the seiche a period at all comparable with that of which we have reason to suspect the existence in the Antarctic Sea," namely, a three-day period. From these observations Darwin makes a "guess," and says, "I guess then that the bay behind the (Ross) barrier stretches past the South Pole and a little to the east of it as far as latitude 80°. Such an inlet would have a length of 25° to 30° of latitude. "A sea of from 100 to 150 fathoms in such an immense bay as has been conjectured would oscillate with a period of three days, and the observed results are seen to be consistent with the existence of a deep inlet, almost or quite cutting the Antarctic continent in two."
"Such a conclusion is interesting, but it would not be right," Darwin wisely adds, "to attribute to it a high degree of probability, because there are elements of uncertainty on every side." Still it is one more of those intensely interesting Antarctic problems which emphasise how much need there is for further Polar exploration.
Tidal observations were taken on board the Scotia every half-hour from March 25th to November 23rd, 1903, when the ship was frozen in in Scotia Bay. The device adopted for recording the tides was a simple one. A heavy weight with an attached piece of sounding wire was lowered over the ship's side, through a hole in the ice-floe in which the Scotia was frozen, to the bottom, which was here 10 fathoms. This wire was led over a block suspended to a davit, and at the end of the wire, on board ship, a second lighter well-shaped weight with a horizontal base was attached, and was suspended in such a way that it rose and fell up and down the face of a wooden scale. The floe in which the Scotia was frozen moved with the tide, the height of which was thus shown by the position of the movable weight on the scale.