Memoirs of the National Academy of Sciences (Volume 14) (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1886 edition. Excerpt: ...afforded by the employment of a smaller star as a standard of comparison have been found to be practically quite as great as had been anticipated, which is made most evident by the diminished value of the mean errors, both for the distances and for the position-angles. And, although a larger object-glass has since been brought into use, and the errors in the determination of the position-angles have been very essentially diminished since the photographs, of which the measures are here computed, were taken; these seem richly worth the labor of a careful discussion, if only for the additional evidence which they aiford of the trustworthiness of pho. tographic methods. The impressions were as follows, all of them from an exposure of five minutes, with an objectglass of 111 English inches aperture: s. Mis. 30, pt 2-13 For determining the refractions and zeroes of position we have likewise, using the same notation as before: Adopting the same value as before for the micrometer screw, viz, 27'.49 at the temperature of 68 F., the distances and position-angles from the central star were first determined, then referred to the mean equinox of 1867.0, and finally the position-angles at the central star converted into one-half their sum for the two stars. To refer the zeroes of the several impressions to the mean value for all, the following corrections were found desirable: The reduction of the observations gives, then, the appended results, in which the position-angles have been modified by the application of these corrections. The resultant mean errors are also given, both for a single measurement and for the final means. 1 25 I 27 l 25 t 20 30 31 II II II II 1384. 01 2301. 70 2293. 50 1530. 13 2424. 03 5. 01 1. 72 3. as 30. 30 3. 22 4. 44...