And Lest I Should Be Accused Of Raising Expectations Which I Do Not Justify, I Will Do My Best In A Digression, Probably Not Unwelcome, To Bring Them Before The Eyes Of My Readers.

"The larger of these instruments were four in number.

First we inspected a great globe [A], graduated with meridians and parallels; we estimated that three men would hardly be able to embrace its girth.... A second instrument was a great sphere [B], not less in diameter than that measure of the outstretched arms which is commonly called a geometric pace. It had a horizon and poles; instead of circles it was provided with certain double hoops (armillae), the void space between the pair serving the purpose of the circles of our spheres. All these were divided into 365 degrees and some odd minutes. There was no globe to represent the earth in the centre, but there was a certain tube, bored like a gun-barrel, which could readily be turned about and fixed to any azimuth or any altitude so as to observe any particular star through the tube, just as we do with our vane-sights;[8] - not at all a despicable device! The third machine was a gnomon [C], the height of which was twice the diameter of the former instrument, erected on a very large and long slab of marble, on the northern side of the terrace. The stone slab had a channel cut round the margin, to be filled with water in order to determine whether the slab was level or not, and the style was set vertical as in hour-dials.[9] We may suppose this gnomon to have been erected that by its aid the shadow at the solstices and equinoxes might be precisely noted, for in that view both the slab and the style were graduated.

Enter page number Go  Previous Next
Page 1231 of 1256
Words from 335218 to 335524 of 342071