Farrow's military encyclopedia : a dictionary of military knowledge . e A« Jioulenge(!hriitijr<ij //. MICROMETER An instrument used with a tele-scope or microscope to measure small distances, O!the apparent diameters of objeels which subtendvery small singles. The micrometer with a gradu-ated scale is used for measuring distances by directcomparison. The apiilication of the micrometer tothe telescope is credited by Whewell to Huyghens,Malvasia and Azout. It was a great advan<e in theattempt to do by accuracy of measurement what hadpreviously been attempled, and in part accom]ilished,by e
Farrow's military encyclopedia : a dictionary of military knowledge . e A« Jioulenge(!hriitijr<ij //. MICROMETER An instrument used with a tele-scope or microscope to measure small distances, O!the apparent diameters of objeels which subtendvery small singles. The micrometer with a gradu-ated scale is used for measuring distances by directcomparison. The apiilication of the micrometer tothe telescope is credited by Whewell to Huyghens,Malvasia and Azout. It was a great advan<e in theattempt to do by accuracy of measurement what hadpreviously been attempled, and in part accom]ilished,by enlarging the instrument so as to enable the meas-urcmenls of smaller arcs. The first micrometer onrecord is that of Gascoigne, of England, constructedabout l(i4l), and used by him in measuring the diam-eters of the moon and some of the planets. Theinstrument had nicely-ground parallel edges of brass-plate, and parallel hairs were substituted by the re-nowned Dr. Ilooke. The drawing shows the micrometer used with theEngineers Transit and other standard It consists of a compound cross-wire ring or having three horizontal wires, of which themiddle one is cemented to the ring, as tisual, whilethe others, lb and cc. are to small slides,held apart bv a slender brass spring lioo)i, and ac-tuated by independent screws, dtt. by which the dis-tance between the two movable wires can be adjustedto include a given space, as one foot on a rod onehundred feet distant. These wires will in the samemanner include two feet on a rod two himdn^d feetdistant, or half a foot at a distance of fifty feet, andso on in the same proportion, thus furnishing ameans of measuring distances, esjjecially over brokenirround. much more easily and even more accunttelythan with a tajie or chain.—See Engineers anil Stadia. MICEOPHONE. 330 HICBOSCOFE. MICROPHONE.—This instrument, invented in 18by I^rnf. Hiijrlios. does for faint sounds what tlicmicroscope
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Keywords: ., bookcentury1800, bookdecade188, booksubjectmilitaryartandscience
