. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biography, geography, commerce, etc. of the world . 1837; d. near Salisbury, England, 27July, 1890. Starting in life as an itinerant thodist preacher, he held prominent Unita-rian pulpits in Chicago and Boston, and becamenoted as a preacher and lecturer. In later lifehe <■■■■- London correspondent of the New YorkHerald. Besides religious writings he publishedHenry Irving, a Sketch and a Criticism ;English Home Lift (1885). Collimation, Line of. In a measuring tej ere i- placed at the focu
. The Americana : a universal reference library, comprising the arts and sciences, literature, history, biography, geography, commerce, etc. of the world . 1837; d. near Salisbury, England, 27July, 1890. Starting in life as an itinerant thodist preacher, he held prominent Unita-rian pulpits in Chicago and Boston, and becamenoted as a preacher and lecturer. In later lifehe <■■■■- London correspondent of the New YorkHerald. Besides religious writings he publishedHenry Irving, a Sketch and a Criticism ;English Home Lift (1885). Collimation, Line of. In a measuring tej ere i- placed at the focus of the eye- tem of spider-threads. In a transit nt there are several vertical and two horizontal wires, as shown in the diagram. In taking an observation the time at which the h wire is noted. Taking tnc nv mes, we obtain what is •he time for the m<an wire, an imagi- na- .vhirh would, if the adjustments were ith the middle vertical wire. .tio:is gives abetter re- than if only one central wire were used. The illbnation is denned to be the straight of the object-glass •laginary vertical wire midway between the two horizontal wires. A. Spider-lines. definition similar to that here given applies inother cases, in the case of the mural circle, forexample, and in the case of instruments for terrestrial proper adjustmentof the line of collima-tion of these instru-ments is one of themost important of theadjustments. In thecase of the transit in-strument, for instance,in observing the pass-age of a star, what isnoted is practically theinstant, according tothe observatory clock, when the line joining thestar and its image coincides with the line ofcollimation. The following is one of the condi-tions to be satisfied when the instrument is inperfect adjustment. The line of collimationmust be perpendicular to the geometrical axison which the telescope revolves, and will thendescribe a great circle. The framework thatcarries the spider-lines admits of several s
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