The Annual of scientific discovery: or, Year-book of facts in science and art . e larger portion of the spy-glass maybe placed in a vertical case; as, forexample, hi the head of a cane. Con-venience in holding, travelling, andeconomy of space is thus secured, whilethe power of the spy-glass is, hi somerespects, improved. A short instrument, like that shownin fig. 2, when held in the hand, is lessliable to oscillation, and enables theobserver to point it correctly and steady,and to measure by means of an ocularmicrometer the distance to a given point, whenever the absolute size of thebody obser
The Annual of scientific discovery: or, Year-book of facts in science and art . e larger portion of the spy-glass maybe placed in a vertical case; as, forexample, hi the head of a cane. Con-venience in holding, travelling, andeconomy of space is thus secured, whilethe power of the spy-glass is, hi somerespects, improved. A short instrument, like that shownin fig. 2, when held in the hand, is lessliable to oscillation, and enables theobserver to point it correctly and steady,and to measure by means of an ocularmicrometer the distance to a given point, whenever the absolute size of thebody observed is known, and vice versd; it is also very convenient for trans-portation, making a pocket instrument without the usual sliding tubes,•which prevent a correct centring of the lenses. This spy-glass consists of an objective rectangular prism, fig. 1, ground inthe shape of a lens on one of its catheti, and throwing back below, byreflection on its hypothenuse, the horizontal rays from the exterior bodyobserved. These rays meet a second rectangular prism, where, by the laet. 198 ANNUAL OF SCIENTIFIC DISCOVERY.
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectindustr, bookyear1857
