10 ASTRONOMICAL OBSERVATIONS 



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 Formulie. All observed altitudes were greater than 14]°. 



Observations for Lonrjitude 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 E., 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 con- 

 sequence 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 11 3° between the pole and the 

 zenith; Dr. Kane remarks,^ "Some of our instruments, in consequence of the cold, 

 became difficult to manage in consequence of tlic 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 ]\Ir. Sonntag. The following pages contain the 

 same extracted from the manuscript. 



In the reduction, I have adopted the latitude 78° 37^', and the longitude 4'' 43™ 

 28" 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' Avith the greatest accuracy is not of so much importance 

 for the moon culminations, since the result for longitude depends more on the dif- 

 ferences 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. 



■ Page 154, veil. I, of the Narrative. 



