. Spons' dictionary of engineering, civil, mechanical, military, and naval; with technical terms in French, German, Italian, and Spanish . oss-blades a d, df, slide in the grooves i K, g h, dn, so as to admit of the ends c a andc d being made as short as is required. This condition is indispensable, as it is often necessary tomeasure very small crystals, which can only be introduced easily between the two cross-bladeswhen their free ends can be very much shortened. This form, however, of the common goniometer has many inconveniences. The observationsare rendered difficult from the fact that th
. Spons' dictionary of engineering, civil, mechanical, military, and naval; with technical terms in French, German, Italian, and Spanish . oss-blades a d, df, slide in the grooves i K, g h, dn, so as to admit of the ends c a andc d being made as short as is required. This condition is indispensable, as it is often necessary tomeasure very small crystals, which can only be introduced easily between the two cross-bladeswhen their free ends can be very much shortened. This form, however, of the common goniometer has many inconveniences. The observationsare rendered difficult from the fact that the crystal under examination has to be held with onehand, and the instrument with the other. Moreover, in holding it before the eye, to ascertain ifthe cross-blade is in perfect contact with the crystal, continual vacillations and distuibances areproduced, which render anything like a correct observation very difficult. These inconveniencesare overcome by the use of a fixed instrument. The crystal under examination is also fixed on asupport, so that both hands are at liberty. This instrument, Fig. 3306, consists of a semicircle fixed on a rod a b, supported by colum»s pp. The rod a b can be moved horizontally, from rightto left, in the grooves c c, in which are placed small friction rollers, so as to render the movementas easy as possible. The fixed semicircle carries another,/i?, movable on the centre o, and dividedinto degrees ; h ik is a vernier which also moves on the centre, but behind the movable semicirclebetween it and the fixed, to which it can be at any time fastened, and in any required position, bythe thumb-screw k ; this vernier gives the minutes. ^ m is a blade whose movement carries roundthe circle/// ; g is a small stem, the function of which is to support the crystal r, which is firmlyfastened with wax. It is so arranged that it can be lengthened or shortened, be inclined eitherfrom or towards the operator, and capable of turning on itself. It is support
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Keywords: ., bookcentury1800, bookdecade1870, bookidsp, booksubjectengineering
