Treatise on the principal mathematical instruments employed in surveying, levelling, and astronomy : explaining their construction, adjustments, and use. With an appendix, and tables / By Frederick Walter Simms.

  • Frederick Walter Simms
Date:
1844
Catalogue details

Licence: Public Domain Mark

Credit: Treatise on the principal mathematical instruments employed in surveying, levelling, and astronomy : explaining their construction, adjustments, and use. With an appendix, and tables / By Frederick Walter Simms. Source: Wellcome Collection.

    95/176 (page 79)
    at another; thus destroying each other’s effect, the mean result will come out very nearly the same as the observation at the middle wire, if they are made with any tolerable degree of ac- curacy, and if the intervals of the wires are uniform. The annexed Table is an ex- ample of the Greenwich mode of registering observations made with a transit-instrument. The heading at the top of the columns sufficiently explains the nature of their contents. The entre. ‘ 1 Limb © fF Limb. C Capella. Cephei 51 Hev. é Urs. Min. S.P. Sirius. Clock. Mean of Wires. Example of the Greenwich mode of registering Transit Observations. M. Ss. ° 76 90 Ss. H. M 23 50 12 33 |+0 41,32| +0,01 23 52 21 4 3 + 0,05 60 |+0 41,31 23 51 17 5 6 6 20 59,00 6 26 32 6 38 30 5 88 |}+0 41,13 0,00 error of the clock from sidereal time is obtained, by taking the difference between the mean of the wires, and the apparent right ascension of the object as given in the Nautical Almanac; and the daily rate is the differ- ence of such errors, divided by the number of days elapsed be- tween the observations. In ob- serving the sun, the times of passing of both the first and second limb over the wires are observed and set down as dis- tinct observations, the mean of which gives the time of the pas- sage of the centre across the Yen) ee N a ° . Seb od he =< meridian, as is shown in the an- | “énobve nexed example. The wires of the instrument are generally os], .%..2 | placed by the maker at such a @ | cat oO 0 distance from each other, that ea the first limb of the sun shall | | 8 mo conn | have passed all of them before § |&|*8a ‘©S8S | the second limb arrives at the 3 = FSU 13 Som first, and the observer can thus (1 Oboe “| take the observations without g hurry or confusion. ? =e ee One limb only of the moon Ne) + - can be observed, except when her transit happens to be within an hour or two of her opposi- tion; and in observing the larger planets, the first and second limb 3 eee may be observed alternately over 3 By the five wires; that is to say, the ¢ a first limb over three wires, viz.,