ASTRONOMICAL OBSERVATIONS AND REDUCTIONS. 



Of the astronomical observations made by the second Grinnell Expedition, under 

 command of Dr. Kane, those for the longitude of Van Rensselaer Harbor, the 

 winter quarters during 1853-54: and 185-i-'55, were most numerous and most 

 carefully attended to. The geographical location of the shore line, traced by the 

 expedition, depends for its longitude on that of Van Rensselaer Harbor, as the 

 central meridian. The latitude of Van Rensselaer Harbor, or Fern Rock Ob- 

 servatory, was likewise carefully determined, as far as the instrumental means of 

 the expedition permitted. The astronomical and geodetic material collected by 

 the various travelling parties, and required for the geographical position of their 

 tracks, is given in Appendix No. 6, to the second volume of the Narrative of 

 the Expedition. Part of this material was collated with the manuscript, and the 

 revised results will be given, in the present paper, after the discussion of the latitude 

 and longitude of Van Rensselaer Harbor. The record of the observations discussed 

 is taken from the original log-book, or other manuscript documents, belonging to 

 the expedition. The astronomical observations were under the special care of Mr. 

 Augustus Sonntag. The principal instruments for the determination of the geo- 

 graphical positions, were sextants, a Gambey theodolite, a transit instrument, and 

 five mean time chronometers. 



Fern Rock Observatory was established on the northernmost of the rocky group 

 of islets in Van Rensselaer Harbor: the highest point of Observatory Island is 

 twenty-nine feet above mean tidal level. For directions to sites of Van Rensselaer 

 Harbor, it will be sufficient to refer to note 56, page 430, of the first volume of the 

 Narrative.^ 



On the 25th of August, 1853, a general survey of the harbor was made, and on 

 the 12th of September following, the site of the Observatory was selected. This 

 observatory consisted of four walls of granite blocks, cemented together with moss 

 and water, and the aid of frost. These walls were covered in with a substantial 

 wooden roof, with openings in the direction of the meridian and prime vertical. 

 The transit and theodolite were mounted on piers, formed by a conglomerate of 

 gravel and ice, well rammed down, in iron-hooped pennnican casks, and cemented 

 by freezing water. These piers were found as firm as the rock on which they rested.^ 



' For a copy see appendix (No. 1) to this paper. ' See page 116, vol. I, of tlie Narrative. 



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