Pantologia. a New Cyclopędia, by J. M. Good, O. Gregory, and N. Bosworth Assisted by Other Gentlemen of Eminence

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General Books, 2013 - History - 618 pages
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1813 edition. Excerpt: ... hours arc figured round both to the right and left. The hour-hand or index is placed in such a manner under the brass meridian, as to be moveable at pleasure to any required part of the hour circle, and yet remain there fixed during the revolution of the globe on its axis, and is entirely independent of the poles of the globe. In this manner, the motion of the globe round its axis carrying the hour-circle, the fixed index serves to point out the time, the same as in the reverse way by other globes. There is a small advantage in having the. hourcirrle figured both ways, as one hour serves as a complement to XII for the other, and tin: time of tun rising and setting, and vice versa, may both be seen at the same time on the hour-circle. In the problems generally to be performed, the inner eircle is thecircle of reckoning, and the outer one only the complement. Fipr. 5. is a representation of the globe, with Mr. Wright's improved hourcircle at C. In the Philos. Trans, for 1789, p. I, Mr. Smea. ton has proposed some improvements of the celestial globe, especially with respect to the quadrant of altitude, for the resolution of problems lelating to the azimuth and altitude. The il ffienlty, he observes, that hasoccurrert in fixing a semicircle, so as to have a centre in the zenith and nadir points of the globe, at the same time t' at the meridian is left at liberty to rai."e the pole to its desired elevation, I suppose, has induced the globe-makers to be contented with the atrip of thin flexible brats, called the quadrant of altitude; and it it well known how imperfectly it pei forms its office. The improvement bare attempted, is in the application of a quadrant of" altitude of a more solid construction j which being affixed to a...

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