MAGNETIC DECLINATION. 5 



Mr. Bonsai, as well as to George Stephenson, for their zealous and intelligent co- 

 operation with Mr. Sonntag and myself." Each set of observations extends over 

 twenty-four hours; they were taken nearly one minute earlier (between 56* and 40 s ) 

 than indicated in the abstract. The general remark on page 435 of the second 

 volume of the Narrative, " the scale reading 280 corresponds to a magnetic declina- 

 tion of 108 3' west, etc.," appears to leave no doubt that the instrument was left 

 undisturbed, and there being no statement to the contrary, we can assume the 

 hourly and daily means at the several days of observation to refer to the same zero 

 or to be comparable amongst themselves. At a later period in June, 1854, the 

 azimuth circle appears to have turned about 19 minutes. 



Term-day Observations. There were six in number. The observations com- 

 mence at 10 P. M., mean Gottingen time, or about 4 h 37 m 34 s mean Fern Rock 

 time, the difference of longitude being assumed to equal 5 h 22 m 26 s . The obser- 

 vations were not taken at the precise instant as indicated in the abstracts ; the 

 small deviation is noted at the head of each table. 



Absolute Declination. The expedition not being provided with a proper instru- 

 ment, the magnetometer was temporarily converted into a declinometer by Mr. 

 Sonntag, who determined the declination on June 9th, the 14th, and the 26th, 

 1854. The top of a mountain was used as a mark; it bore south 22 west 

 (magnetic). 



The mirror attached to the magnets can be inverted so that the mean reading of 

 mirror direct and mirror reversed corresponds to the reading of the magnetic axis 

 of the magnet. 



Geographical Position of Observatory. The latitude and longitude of the astro- 

 nomical observatory has been determined as follows: Lat. 78 37'.0 north, Long. 

 70 40' west of Greenwich. (See p. 305, vol. II. of the Narrative, also pp. 385 and 

 387 of the same volume.) The island (Observatory Island) on which the obser- 

 vatory (Fern Eock Observatory) was placed, was some fifty paces long by perhaps 

 forty broad. (See p. 116, vol. I. of Narrative.) The magnetic observatory was ad- 

 joining; it was of stone, ten feet square, with a wooden floor as well as roof, and 

 supplied with a copper fire grate. No iron was used in its construction. 



The following is an extract of note 56, p. 464, of vol. I. of the Narrative: "The 

 subjoined are given as aids to physical inquiry on the part of future travellers: 

 Directions to sites of Rensselaer harbor. The observatory was placed upon the 

 northernmost of the rocky group of islets that formed our harbor. It is seventy- 

 six English feet from the highest and northernmost salient point of this island, in 

 a direction S. 14 E., or in one with said point and the S. E. projection of the 

 southernmost islet of the group. A natural face of gneiss rock formed the western 

 wall of the observatory. A crevice in this rock has been filled with melted lead, 

 in the centre of which is a copper bolt. Eight feet from this bolt, and in the 

 direction indicated by the creviQe, stood the magnetometer. This direction is 

 given in case of local disturbance from the nature of the surrounding rocks." 



The highest point of the island was about thirty feet above the mean tide level 

 of the harbor. The observatory was known by the name of " Fern Rock Ob- 

 servatory." 



