REMARKS UPON LONGTITUDE.

Otago Witness, Issue 1239, 28 August 1875, Page 7

REMARKS UPON LONGTITUDE.

MADE BY MR j. t. THOMSON, P.R.G..S

BEFORE THE OTAGO INSTITUTE.

The person known to the Western World aa being the first to determine longtitude was Hipparnhus, of Nicea, B.C. 162. He established degr fi es as commencing from the Insulae Fortunate, or Canary Islands. But as the principle of the rotundity of the earth was taught by more ancient astronomers, so also must they have been acquainted with lon*, titude. Thus the Egyptian, Chaldean, and Hindoo astronomers of Thebes, Babylon, and Palmibothra respectively must have noted the differences of time in the occurrence of eclipses, and hence their differences of longtitude. Tiazzi Smith, who has given great attention to. the mathematical characteristics of the Great Pyramid of Gyzeh, has amongst many other things pointed out that the measurements of the central cist indicate a knowledge of the solid capacity of our globe. To do this would require a knowledge of its sphericity, and hence a knowledge of longtitude.

Amongst the ancient Greeks, Thales Who flourished 640 8.C., and Pythagorus 080 8.C., maintained that the worfd was round. Amongst the Romans, it may be mentioned that Cicero, with many inconsistent views, held the same doctrine The great geographer Ptolemy, who lived ; ' } • ', • ad the de B r ees of longtitude placed rahis maps, apparently in imitation of Hipparchus. But science makes very slow inroads on the convictions of primi, tive feeling, and reason, however well teamed, can never entirely displace these, lhus, though the roundness of the world might m course of time be very generally admitted by those who took the trouble to think anything about the subject, yet to grasp the idea that the world was not a fixture, and that it revolved round the sun as a centre, appears to have been a great struggle for the human understand, ing Thus we find, in mediseval times, that the scholastics accepted contrary views which, even up to our age of revived aits and learning, they held aa a religious dogma, In this wise Galileo came in contact with them, at that time a power who had influence enough to cause his torture and banishment. " But we must not think that we have even got rid of the idea of the flatness of the earth. Counting heads of the whole population of the world, it will be found that the vast majority believe in this. It is still maintained universally, by Mohamedans and Buddhists. A Mahomedan will say " Does the Koran notfteach us that God has spread out the earth as a carpet, and wit not surrounded by the mountains of Kaf, and again are these not surrounded by the sea of Kulgoon ?" A Bhuddist will tell you, when you show him how ships and mountains sink under the horizon as we recede from them—" Ah ! true, here ! but it may be otherwise beyond !" But we not go far to find opposera to the earth's sphericity. A late notable instance is of an Englishman having staked £500 on the subject against the famous naturalist Wallace, and lost his bet ; and even on this coast I have seen a shipmaster, with apparent sincerity, stoutly combat the idea.

Mr Thomson then shortly [described the instruments used in determining lon»titude, commencing with the Arab asstronomers of the 10th century. He noticed those in use by Captain Cook, who fixed a position in this Province (Pickersgill Harbour), by independent observations, to within seventeen minutes in arc of the late determination by Stokes He then described the mode of finding'lon«titude at sea— lst, by chronometer : 2nd by lunar observation ; 3rd, by altitude of moon ; 4th, by eccultation ; and sth by eclipses of Jupiter's satellites-showing tiie principles and giving the mathematical formulas. He then touched on the modes on land, where all the preceding were available, but pointing out the system most had recourse to in the use of the transit instrument, where— «Si of?^ tonometer might be used ; 2nd, differences of time by nonculminating stars ; 3rd, differences of star transits by electric telegraph ; 4th, differences of space by triangulation. ' He concluded by exhibiting Morse's register, and showed its application as a chronograph, when attached to &edth I* J T termg t0 the areatu part of a second.