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Nature volume 49, pages 209210 | Download Citation

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SMALL DISTANCES MEASURED WITH THE HELIOMETER.—As the filar micrometer measures very precisely distances of a few seconds, so with equal accuracy does that important of modern instruments, the heliometer, measure distances ranging from a few minutes up to one or two degrees. With the former instrument one brings the thread (moved by the micrometer head) first to one side of the star and then to the other; or, if one has two threads, one places the star half-way between them, and thus reads off the distance. With the heliometer the distances are read off the scale at the object-glass end (from the eye end), the images of the two stars cast by the movable half of the object-glass being placed symmetrically first on one, and then on the other side of the images from the fixed half.

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https://doi.org/10.1038/049209a0

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