FIXING THE POLE.

Dominion, Volume 5, Issue 1385, 11 March 1912, Page 5

FIXING THE POLE.

HOW AN EXPLORER CAN TELL WHEN HE IS THERE. VARIOUS METHODS DESCRIBED. A claim to have reached the Polo must of course be substantiated by adequate proof. In' the "Popular Science Monthly"' for January, 1910, thero appeared an exceptionally clear explanation of what proof is possible and necessary. The articlo was written by Professor 11. !•'. Heid, of John Hoplcin s University, in view of the North Pole controversy, but those portions of it which are applicable to South Polar conditions we reprint below:— Let us say, in the first place (begins Professor Rcid), that neither photographs, which only show the condition of the ice, but do not indicate whether they were taken near (he pole or several hundred miles from it, nor the testimony of human beings, gives any evidence whatever that an explorer lias been to the Pole. Persons who were not actually with the explorer can only express their confidence in his good faith, in his knowledge of the proper astionomical observations to be made, and in his ability to make them with sufficient accuracy-. Persons who accompanied Mm could only vouch for the fact that he did not remain in camp at n comfortable distance from the, Pole and manufacture observations, but that he actually travelled in the general direction of (ho Pole, that on a certain date he claimed he was there, and that lie made frot|iieiit astronomical observations on the route. The Only Real Evidence. Tho only evidence which can at all jatisfoctoriiy show that, nn explorer hn* been near the Polo i.« I hat afforded liy nlvsarvatinns on the euu or stars, capable.

of determining his successive positions nt tho times they were taken. _Other evidence might prove the negative; such as inconsistencies in the narrative, inade(jUiit'P time or insullicienl food for (ho distance travelled, the description of phenomena which could not have been seen at the place where the explorer thought he was; ami so on. It is impossible to foresee the many discrepancies which might show that an explorer has not been to the Pole; they will not be considered here, as this article is not controversial, but merely aims to set forth, as simplv as possible, what kind oi observation's must decide (he claim of having reached the pole. If an explorer has measured the altitude of (he sun, and lm« nt the same timo observed the Lireenwicli time by his chronometer, he has merely determined that he is somewhere on a certain circle, whose position he could pint on his map; but other considerations, such as his last determined location, and (he approximate, distance he had travelled from it. would make known more or less roughly m what part of the circle he was; bill ho could not determine his position accurately. If, some time after his first measure of (he sun's altitude, he should make a second similar measure, he *would determine his position on a second circle; and tho intersection of those two eire es would determine his position completely. The determination, of course, would lie more accurate if the circles cut each other at a high, angle, and this coind bo instiled by making the second set of observations" on the sun after it hail changed its direction (measured, on tiic horizontal plane) bv about !10 degrees. Instead of making two sets of observations on the sun, we might, in the evening, observe two stars properly located wnh

respect to each other and wo could then find two circles of position in a few minutes, and completely determine our position. Sumner's Method. If tho sun is duo north or south, tho part of tho circle on which the observer is will coincide with his parallel of latitude, which is thus immediately determined; if the sun is dub east or west, a part of the circle will correspond with the meridian, and longitude will bo found. The old method of determining position at sea, and one still in use, wua to observe the sun at noon for latitude, and to accept as local noon tho poorlydetermined time when the sun reached its highest altitude; or to observe also in the morning or evening for timo or longitude, guessing at the latitude to work out the observations. But the now method makes it possible to observo altitudes at'any time, and to get satisfactory results even if the sun were hidden for several hours during the middle of the day. And, besides, it makes clear just what information regarding our position is'yielded by a single observation of tho sun's altitude. This beautiful method was first used by Captain Thomas H. Sumner, of Boston, Mass., in 1837; tho short parts of tho circle which are drawn on tho map in rinding one's position are called Sumner's lines. If an explorer were approaching the North Pole, and had arrived, let us say, within a degree of it, it would be necessary for him to determine his latitude in order to know his distance from the Pole, and to determine the direction of the Pole in order to know his course. It might bo supposed that when approaching tho Pole he would, by means of his compass, be ablo to follow his meridian; but the difficulty of keeping a fixed directum, when travelling over rough ice, and rs-' pccially the shifting of his position by tho unknown drift of the ice, would soon made a decided change in his longitude in a region where tho meridians converge so rapidly. By means of his chronometer, keeping Greenwich mean time, the explorer could determine the direction of any meridian, for tho sun would be on tho meridian of Greenwich at Greenwich noon, and would move 15 degrees in longitude for every hour thereafter; this knowledge would be very valuable to enable him to lay out his return course from the Polo to* his base of supplies; but it would not, in ignorance of his meridian, help him to find the Pole; lor tln> direction of the Pole in relation to tho direction of the sun, or of tho compass needle, does not depend upon the general direction of the meridians, but upon the particular meridian on which he happens to be. An Apparent Anomaly. We havo thus the apparent anomaly that the same observations would enable a person to set a satisfactory course away from tho Pole, but not toward it. But the anomaly is only apparent; for, suppose tho bate of supplies were on the 70th meridian and in latitude 83 degrees; and suppose the explorer were near tho Polo and twenty miles from tho 70th meridian, on one sido or the other;_ ho could lay a course parallel with tho 70th meridian, and this direction would only ■differ by about u third of a degree from the most direct line to his baso of supplies; but if he kept this course accurately, ho would miss his baso by tiventy miles. This, however, would be less important than missing tho Polo by tho same distance. The very simple method of determining latitude by the altitude of the sun when on tho meridian would not be available to the explorer, for his meridian would not bo known; and it would rcquiro a set of observations extending over several hours to learn when the sun was on his meridian. To determine his position, and the direction of the Pole, the explorer must fall back on the method of Sumner s lines, and fortnnatelv they can be applied with, special facility in the neighbourhood of the Pole. ~.,., u j Aft»r describing in detail the method of Sumner's lines, the writer proceeds:An explorer mav find his position by pure calculation, and may not use the graphic method described, but the principle in the two methods is exactly tho same, and the graphic method shows, more clearlv what the observations mean. An 'important source of error eiucrs all the-e ob-ervatimi=, namely, atmospheric refraction, or the bending down nl the light rnvs as (hey pax through he atmosphere. The amount ol this bonding i:irrca<-cs rapidlv a> the sun is nearer the horizon: it al-o varies with die barnmetric procure, and with the temperature ... 11. however, the observer «hnuld wait for Iwonlv-fnnr hour.- after his fir-l observation, aiid should measure a fifth altitude of'the snu. he .-mild find a fair correction for the refract ion, timl greatly improve the determination of his position.

Time Needed at the Polo. II: would be unrea'-onable to expect nn explorer, making » dash for Hip iuilc, to remain twenty-lour or even eighteen hours nt 0110 tamp for the purpose of exact 1 y determining his position. Ity making daily observations un the sun, at different hours, so as no!, merely to lis Ill's successive positions on a scries of parallel lines, but un lines having different directions; by keeping his liireclion with the compass anil estimating the drift of the ice and his rale- of travel, ho could always know where he was without too large an error. lint when he was iu the iminedi;i(e neighbourhood of (lie pole he should make as many observations with the sun in different directions, as circumstances would permit. Patiguc, severe cold, the condition of his commis-nriat, anil the anxiety to return after having succeeded in his bold undertaking, might prevent him from making as ninny observations as would bo desirable; but', nevertheless, they might be sufficient to be convincing that he had been within u few miles of the Pole; it would surely bo a quibble to dispute with an explorer the honour of having reached the Pole if his observations showed, without reasonable, doubt, (.hat ho had been within ten or fifteen miles of it. There aro two kinds of instruments nsod for measuring altitudes; the transit-thco-dolito anil the sextant. Tho former consists of a telescope so mounted that it can turn in a vertienl and in a horizontal plane; it is provided with vertical OT(l horizontal graduated circles, to measure the angle turned through, and with levelling screws ami spirit levels to adjust it ill position. It is supported by a tripod, and after being properly levol-

led, the reading of the vertical circle gives the altitude of (he object sighted through the telescope. It is by far tho best instrument for an explorer on land, it is very easy to use, and its adaptation to measure horizontal angles onables the explorer to carry on an ordinary survey. Use of the Sextant, Tho sextant was originally invented for uso at sea, where a steady 'support Cannot be found. It consists of a' telescopo mounted on a frame, which is held in iiie hand. To measure the nnglo between two objects, one of them is sighted directly through the telescope, and tho image of the second h reflected into tho telescope by means of two mirrors, ono fixed rigidly to tho frame in front of the telescope, uiul covering half its field, and tho other movable around an axis fastened to the frame. The movablo mirror is turned by an arm, which moves along a graduated arc on the frame, and its reading, when the two objects appear in tho teiescopb superposed upon each other, gives the anglo between the objects. In determining the altitude of tho sun at sea the edge of the sun is made to touch tho horizon; a movement of the ship moves the sun and tho horizon together, and tho contact is not destroyed. On land, when the sea horizon is not available, a so-called "artificial horizon" must bo used. The ordinary mercurial artificial horizon consists of a flat dish about threo inches wide and five or six long, filled to a small depth with mercury, the surface of which becomes perfectly horizontal. Tho image of the sun seen in the mercury will be as much below the horizontal piano as tho actual sun is above it; and the angle between the sun and its imago is twice tho altitudo of the sun. Except in very quiet air, the surface of the. mercury must bo protected from tho wind by an accurately-made glass cover. The glass artificial horizon is a piece of perfectly flat dark glass, which will absorb the light which enters it, and only reflect from its upper surface. It is provided with levelling screws and spirit levels so that it can be made perfectly horizontal. It is used in exactly the same way as a mercurial horizon. Each form has its advantages; the glass horizon is easily transported, and can be used at temperatures below tho freezing point of mercury (about 39 degrees below zero Faronheit)." On the other hand, it requires very careful levelling, and is liable to bo broken. The mercury of a mercurial horizon is usually carried in an iron bottle; in pouring it back and forth it might bo spilled and lost; and at very low temperatures it would be necessary to heat it to keen it liquid; but then it immediately takes'a level surface and Tequires no levelling. What Shackleton Used, Lieutenant Shackleton travelling over tho Antarctic continent determined his position by means of a small transit. Commander Peary and Dr. Cook travelling over the floating ice of tho Arctics, used sextants. Tho former used a mercurial and the latter a glass horizon. It is interesting to nolo that if a man were taking an observation standing, with the sun about 6 degrees above tho horizon and tho artificial horizon on the level of his feet, it would havo to bo about 45 feet from him, and as ho would look at it from an angle of about 6 degrees, it would only appear about half an inch long. If tho altitude 'of tho sun were 12 degrees, the artificial horizon would bo 25 feet away, and appear about an inch long. This enn be easily imitated by putting a sheet of paper on the ground and looking at it from distances of 25 and 45 feet Under such conditions tho difficulties of making a good observation would be much increased. If however, tho artificial horizon were raised on a support, tho observer would stand much closer to it, and the observation could bo more easily made. Another important instrument is tho chronometer keeping mean Greenwich time; for, as has already been shown, the determination of position in general requires a knowledge of Greenwich time, though at the Pole itself this is not necessary. Whenever an explorer remained as long as a week in ono place he should determine, as well as he could, how much his chronometers were gaining or losing per day; and he should be most particular to determine the changes in their errors, between the times of leaving and returning to his base.station. A compass is of groat value to keep one's course between observations on the sun; <md an aneroid barometer and a thermometer make possible a more accurate correction for refraction. A potlunioti'i', al.-o, or some other Form of dis- ! I.ance meter, would be u-cl'ul to estimate ! the distance travelled. British Furthest South. i Although tho methods o[ determining o'uo's Eoozraphical position would bo the

sa near cither Polo, thcro are slight differences in their applications; for instance, the solid luml of (ho Antarctic conliiii'iit precludes drift, nnd therefore litis disturbance is absent. Aloieover, when Lieutenant Shackleton reached his farthest, south in Hit! beginning of Jamimv, l!lll!l, tho sun was aliinit iii degrees above the horizon; nt this altitude tho refraction is not large, and its value is well enough lwiown not to introduce any great error. Near Lieutenant, Shackleton's base enni]). Nt the foot of Mount Erebus, tho North l'olis of the compass needle pointed uliout 31) degrees cast of south. Along (ho most southerly p;rt of his roule, on his dash toward lltG p.ilc, the imrlh end of Hie needle pointed ••cry nearly to the South i'olo. (lit tho return trip ],ieuleuant Shacklcton could have been guided W his cumpass, by tho niountaiii range which ran very nearly parallel with his loule, or by other 'landmarks, and, perlui«, to some extent, by his tracks: so that ho found it mi necessary to make many astronomical observations. Commander Peary was guided, to a great extent, in his return by his tracks and liiose of hi? supporting parties; and Dr. Cui'c seems to have relied entirely on his astronomical observations. Note—For the sake of simplicity the sun has boon generally taken, in this article, as the heavenly body on which observations aro made. but the stars could serve equally well, and, for soino observations, better. If tho Pole should be approached when tho stars were visible, the altitudes of two stars lying <m" meridians about 00 degrees apart woukl determine one's position witluni del'iyj moreover, stars could lie srbi'tml whose altitudes wero sufficiently great to Willi's errors due to refraction; or this correction could be determined by obsr.'vii.tionß on a pair of stars having about the same, altitude and lying on opposito sides of the zenith. The sun's apparent motion around tho earth is not uniform, and therefore a correction, known as tho "equation of time," must be applied to all observations on the sun; but this correction is accurately known and leads to no error.