SECTION XIX. 273 Then while London stands under the meridian, the true and real situation of it is exactly represented on the globe with its proper horizon : For London is by this means placed in the zenith, or on the very top of the globe, at 90 degrees distance from the horizon every way ; and thus the zenith is as high above the equator onthe south side as the pole is above the horizon on the north side. To render this representation of the situation of any place yet more perfect, 'tis a useful thing to have a small mariner's compass at hand with a,needle touched witha load stone, to shew which are the northor south points of the real horizon, and then as near as you can, set the brazen meridian of the globe exactly north and south. Thus the recoden horizon will be a perfect parallel to the real horizon, the brazen meridian to the real meridian, the equator, the ecliptic, and all the lesser circles, and the points on the globe will represent those circles and points on the earth or in the heavens, in their proper position. Problem VIII. " The hour being given in any place (as at London) to find what hour it is in any other part of the world." Rectify the globe for London, bring the city London to the side of the meridian where the degrees are marked ; then fix the index of the dial-plate to the hour given (suppose four o'clock in the afternoon) this being done turn the globe and bring any place successively to the meridian, then the index or hour pointer will spew the true hour at the place required. Thus when it is four o'clock in the afternoon at London it is almost five at Rome, near six at Constantinople, 'tis almost half an hour past nine at night at Fort St. George in the East Indies, 'tis near midnight asPe- kin in China, 'tis eleven o'clock in the morning at Jamaica, and a little past noonat Barbadoes. Problem IX.'" To rectify the globe for the zenith." After the former rectification for the latitude of the place, fasten the edge of the out of the quadrant of altitude on its gra- duated side at the proper degree of latitude on the graduated side of the brazenmeridian, and that will represent the zenithof that place in the heavens. The quadrant of altitude being thus fastened serves . to measure the sun or star's altitude above the horizon, and the sun or star's azimuth ; and it has been some- times (though erroneously) used to shew the bearing of one place to another, as in the following problem. ProblemX. " Any two places being given, to find the bear- ing from one to the other," i. e. at what point of the compass the one lies in respect to the other. Thecommon waywhereby several writers have solved this problem is this: Rectify the globe both for the latitude and for the zenith of one of those places, and bring that place todhe Vol., mt.
RkJQdWJsaXNoZXIy OTcyMjk=