May 16, 1854. Observations of circum-meridian altitudes of the sun, for latitude. Gambey sextant; on the floe near the brig. Pocket chronometer. Double altitude. Pocket chronometer. Double altitude. !! Hour angle Reduction to meridian O's declination Resulting latitude + 0.5 and +19° 08′ 08′′ + 5 58 +15.1 +19° 08′ 12′′ P. M. Pocket chronometer. Double altitude. Pocket chronometer. Pocket chronometer. Double altitude. Pocket chronometer. A. M. P. M. The reductions of observations of equal altitudes are made according to the method given in the American Ephemeris and Nautical Almanac, for 1856. On reducing the observations, it was found that the chronometer error came out too small by 24.5; and, after working each set separately, the discrepancy was traced to the morning observations. The following reductions, therefore, are based on the two sets taken in the afternoon. It is probable that there was either an 1 For chronometer error see following observation. unusual amount of refraction in the morning, or else the rate of the chronometer has changed in the interval. . Pocket chronometer. Double altitude. Pocket chronometer. Pocket chronometer. Double altitude. Pocket chronometer. P. M. P. M. A. M. May 17, 1854. Observations of circum-meridian altitudes of the sun, for latitude. O's corrected altitude (for index, refraction, and parallax) 30° 44′ 31′′ 30° 44′ 31′′ 4h 38m 578.8 - 4 39 24.4 23 59 33 + 3 26 5".0 +19° 21' 49" +19° 21' 45" 78 37 10 78 37 13 78 37 12 May 19, 1854. Observations of equal altitudes of the sun, for time. Pocket chronometer. Double altitude. Pocket chronometer. Pocket chronometer. Double altitude. Pocket chronometer. A. M. P. M. A. M. P. M. RECAPITULATION OF CHRONOMETER ERRORS DETERMINED IN MAY, 1854. May 16. Pocket chronometer fast of Fern Rock mean time. 4h 39m 24.9 4 39 24.4 4 39 21.8 The pocket chronometer was made to indicate Greenwich mean time within a few minutes; between October 5 and October 10, 1853, it ran down; October 29, it was carried about for nine hours; again, November 4, it was carried on a journey for three days; on the 22d of November it ran down, and on December 21 it was exposed for four hours to a temperature of -38° F. Its rate, as indicated by the other chronometers, 2143, 370, 2721, and 264 (all mean time chronometers), was tolerably uniform, and varying between 3.6 and 0o.0. May 20, 1854. Observations of circum-meridian altitudes of the sun, for latitude. RECAPITULATION OF RESULTS FOR LATITUDES OF VAN RENSSELAER HARBOR. September 12, 1853. From two sets of Z. D.'s of the sun at the Fern Rock Observatory 78° 37′ 44′′. This result will be used for the reduction of the transit observations at the observatory. This observatory was some distance (as we learn from pages 108, 116, 167, and 168, of vol. I, of the Narrative) to the northward of the position of the brig. The following results for latitude refer to the position of the Brig Advance in the winter quarters: 1 The recapitulation of the approximate values for latitude of the brig, on p. 387, appendix No. VI, vol. II of the Narrative, has two additional values between May 14 and 15, for which I could not find any record. which result is to be used for the reduction of astronomical observations taken on or near the brig; it gives also the position of the meteorological observatory on the floe. In the above reductions, Ivory's refraction tables have been used, as given in the convenient form for logarithmic computation (and extended if required) in Lee's Collection of Tables and Formulæ. All observed altitudes were greater than 141°. Observations for Longitude of Van Rensselaer Harbor Observatory, and the Winter Quarters of the Brig Advance. OBSERVATIONS OF TRANSIT FOR TIME AND OF THE MOON AND MOON CULMINATING STARS FOR LONGITUDE OF FERN ROCK OBSERVATORY. The transit observations commence November 18, 1853, and end January 10, 1854. The time was noted by the pocket chronometer, showing within a few minutes Greenwich mean time. The transit instrument was supplied with five wires, and the observations are recorded, from I to V, in the order in which the star (or moon) passes them at the upper culmination, the circle being east of the telescope. The letter R, attached to the name of the object observed, indicates that its transit was observed reflected from a mercurial horizon; this method of observing became necessary for the measure of the inclination of the axis, in consequence of the intense cold affecting the length of the bubble of the level to such a degree that it became useless. At temperatures below -40°, no use could be made of the instrument. The instrument was properly adjusted, an operation somewhat troublesome in so high a latitude, and at so low temperatures. For the azimuthal adjustment there remained but an arc of 113° between the pole and the zenith; Dr. Kane remarks,1 "Some of our instruments, in consequence of the cold, became difficult to manage in consequence of the unequal contraction of brass and iron." Appendix No. VIII, of vol. II of the Narrative, contains the record of the transit observations, as made by Mr. Sonntag. The following pages contain the same extracted from the manuscript. In the reduction, I have adopted the latitude 78° 37', and the longitude 4h 43m 28s W. of Greenwich (an approximate result from the moon culminations). The reduction was made by application of the method of least squares; to know the instrumental deviations with the greatest accuracy is not of so much importance for the moon culminations, since the result for longitude depends more on the differences of time between the transit of the moon and stars, but it is otherwise with the occultations, where the chronometer error must be known with the greatest precision. A peculiarity in the construction of the instrument requires to be noticed, viz: it does not permit direct observation of a star elevated more than about 50° above the horizon, hence all observations upon the pole star, and others near the zenith, had to be taken reflected. 1 Page 154, vol. I, of the Narrative. |