The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . o avoid currents from ~~~ possible difference of tempera- ,turo between the mass of ^ metal and the surrounding air; (3) an equatorial mounting capable of direction to any part of the visible hea-vens and of con-tinued observation past the meridian without reversal ; (4) ar efficient means of supporting the mirror without flexure; (5) driving clock; circles to find oridcntifyan
The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . o avoid currents from ~~~ possible difference of tempera- ,turo between the mass of ^ metal and the surrounding air; (3) an equatorial mounting capable of direction to any part of the visible hea-vens and of con-tinued observation past the meridian without reversal ; (4) ar efficient means of supporting the mirror without flexure; (5) driving clock; circles to find oridcntifyan object, and motions taken to eye end ; (6) a , tcicscoro moiiuling which i •« « , , , . » will give Ibo greatest amount of steadiness with tho least amountofjrictiou. ,Fig. 30 is a section of the instrument m the pianopf the meridian. DD, is a hollow cylinder, accn-ralely borrd out, attached to a strong losi> block. Dg is a coverbolted 00 the bottom of this cylinder, ill the centre of which is alappniig steel pin D^, which enters a corresponding hole in tliotottoiu of the polar axis serves .is the lower pivot otTjIoiiIWk Nolvft K >:>?. Vpt »«xix p. 3S<. the polar axis. The cyUndrical of the polar axis is accu-rately turned to a diameter one-eighth of an inch less than the outericvlinder, and the otherwise severe friction on the pin Dj is reUevedbv filling in the space between D and E with mercury, so lar assufficient nearly to float the whole moving part of the upper elbow-shaped part of the polar axis Ei is flanged andbolted to the lower part. In the section at right angles to thatexhibited in fig. 30 this elbow-shaped part is T-shaped, and thecross of tho T is bored to receive the declination axis ; and, a3the elbow puts the polar axis considerably out of balance, theT-shaped head is carried forward of the axial line about U inches,so that the whole weight of the telescope above just restores thebal
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Keywords: ., bookcentury1800, bookdecade1890, bookidencyclopedia, bookyear1892
