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. 1882 edition. Excerpt: ...B Cygni, and also some further measurements of 61 Cygni, and as some of the distances measured are large, it seems necessary before making the reductions to give an account of the-various results found for the value in arc of a single revolution of the screw of our filar micrometer. 2. The first determination of the value of one revolution of the screw was made by Prof. Simon Newcomb. His results are as follows: weight zz 2 zz 1 zz 1 ZZ I "= 1 The mean value is R zz 9."g022 zfc: o."oo486 This value was found by observing transits of stars with a non-achromatic eye-piece, which was moved between transits over the two wires. In 1875 Professor Newcomb made another determination in which the eye-piece was not moved during the transits lie found the result R zz 9."902 o."oo8 Soon after the mounting of the 26-inch refractor Prof. Edward S. Holden began an elaborate series of observations for the determination of a definitive value of a revolution of this screw. His investigation includes a variety of methods, and the results, including some obtained by Professor Newcomb and myself, are given in Appendix I to the volume of the Naval Observatory for 1877. They are as follows: From 964 transits of quick-moving stars 14 nights R zz 9.9465 0.0018 wt. zz 45 "16 transits of 36 (H) Cassiopese 2 nights R zz 9.9460 0.0002 " zz 1 "3 meas. of/5, 42, and44 0rionis 3 nights R zz 9.9499 zb 0.0002 " zz 50 "26 meas. of 48, Atlas, and Pleione 3 nights R zz 9.9360 0.0020 " zz 1 "40 meas. of 48. Electra.and Merope 5 nights R zz 9.9409-4-0.0007 "--2 "measures of focal length R zz 9.9390 0.0010 " zz 1 From these determinations we have the final value, ...