The London, Edinburgh and Dublin philosophical magazine and journal of science . n this way a crude range-finder is formed, which suffers froma radical defect, arising from the fact that the beams enter theeye in different directions, so that any alteration in the accom-modation of the eye produces a duplication of the attempt is made to avoid error from this cause bykeeping the eye focussed all the time on cross-wires fixed inthe focal plane of the eyepiece. (2) The short-focustelescope has not usually base enough for accurate telemetry(the maximum available base being the diameter o
The London, Edinburgh and Dublin philosophical magazine and journal of science . n this way a crude range-finder is formed, which suffers froma radical defect, arising from the fact that the beams enter theeye in different directions, so that any alteration in the accom-modation of the eye produces a duplication of the attempt is made to avoid error from this cause bykeeping the eye focussed all the time on cross-wires fixed inthe focal plane of the eyepiece. (2) The short-focustelescope has not usually base enough for accurate telemetry(the maximum available base being the diameter of theobjective), or if it should have base enough, the minimumrange which it can measure is too great. Looked at from the range-finding point of view the problemof optical spherometry and focometry is one of excessivesimplicity. What is required is a range-finder whose^ primereflectors can be fixed at any distance apart (to furnish theadjustable base) and at any angle to that base (to furnish the adjustable range). Fia-. 1. ^N A 0 \2> —5H Ab\/b / N O A / <&/ I y c. One arrangement is shown in plan in fig. 1 and in perspective in fig. 2. A, A are two triangular reflecting Sfjlierometer and Focometer. 93 prisms forming the prime reflectors supported on standsprovided with levelling-screws. Slots S, S are provided inthe frame-piece D through which pass stout pins P, P pro-vided with clamping-screws helow. B, B are fixed reflectorsopposite A and A. respectively. C is an extra reflector(made into one hlock with B and B7) so as to reflect the twobeams upward to the eye. If now the prime reflectors beadjusted for a particular range, the two portions of the objectviewed will appear in coincidence in the field of viewfurnished by C. If the two portions are not in coincidencethey may be brought into coincidence by translating therange-finder to or from the object or image. The instrumentwrorks in fact just like a short-focus telescope, the onlydifference being that the correctnes
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
