TABLE of Magnetical Observations made on hoard of 

 view to investigate the laws by which the Anomalies, or 

 regulated. 



[To front p. 638. Vol. 11. App. N» IX. 

 tlie Ship EsK, in Voyages to the Greenland or Spitzbergen Wfiale Fishery ; with a 

 Errors, discovered in the Indications of the Mariner's Compass on Shipboard are 



11. 



1815 

 June 30. 



1817. 

 June 6. 



July 16. 



III. 



77M9'N. 



77.56 



77.36 



IV. 



12M5' E. 



0.15 W. 



Time. 



[Ck. Chrono- 

 meter.] 

 [^p. Appa- 

 rent.] 



V. 



Ap. Noon. 



CA.6''54'P.M. 



7.28 



7.28 



6.54 



7.32 



7.33 



Ap. 11.38 



11.20 



12.03 



Ch. 7.34 



7.38 



Ch. 6.33 



6.36 



6.31 



6.44 



6.43 



6.41 



Sun's Azimuth. 



VI. 



S. 7°W. 



38 



21 

 N. 36 W. 



35| 



45 



274 



33 



31 

 S.25W. 



27 



34| 

 N. 46 W. 



164 



60 



33 



46 



53 



41 



70 



VII. 



South. 



South. 



South. 

 N. 73°W. 

 6430 

 64.30 

 73.00 

 63.30 

 63.15 



S. 5.30 E. 



10.00 



S.0.45W. 



N. 68.11 W. 



67.11 

 N. 79.54 W. 

 79.09 

 80.24 

 77.09 

 77.24 

 77.54 



VIII. 



7°W. 

 38.00 

 21.00 

 37.00 

 28-45 

 19-30 

 45.30 

 30-30 

 32-15 

 30-30 

 37-00 

 34-00 

 22.11 

 50-41 

 19-54 

 46.09 

 34-24 

 24.09 

 36-24 



7-54 



as 



IX. 

 21° W. 

 21.00 

 21.00 

 32.30 

 32.30 

 32.30 

 32.30 

 32.30 

 32>30 

 36-00 

 36.00 

 36.00 

 37.00 

 37.00 

 33.00 

 33.00 

 33.00 

 33.00 

 33.00 

 33.00 



Errors produced in the observed 



variation by the attraction of the 



ship on the compass needle. 



Error attri- 

 buted to the 

 position of 

 the ship's 

 head. [Diff. 



of col. Till. 



and IX. 



14°.0' 1 

 17.00 j 



0.00. 

 4.30 

 3.45 



13.00 



13. 



.00 \ ) 



1.00 } 

 2.00 1 

 0.15 j " 

 5.30 ■» 

 1.00 ) ■) 



2.00 

 14. 

 13. 

 13.06 

 13.09 



1..49 \ 

 1.41 j " 



3.09 j y 



1.24... j 

 .51 1 



1.24 i Y 



3, 



25.06 



Differences 

 produced by 

 a change in 

 the position 

 of the ship's 

 head. [From 



col. VIII, 



XI. 



6.30 

 3.0 



Differences " 

 produced by 

 a change in 

 the position 

 of the<;om- 

 pass. [From 



col, VIII.] 



Ship's head 

 by the bin- 

 nacle com- 

 pass. 



XII. 



31°.0' 

 17.00 



26.15 . 

 11.45 . 



12.15 . 

 28.30 , 



xin 



S. by E. 



S. by E. 



S.byE. 

 jW.JS. 

 (East. 

 J^East. 

 (W.JS. 

 JE.4S. 

 (e. JS. 



E.byS, 



i: 



jE.by 



E.4 E 



rNNE, 



(nne. 



r South. 

 ■ (South. 



South. 

 ( South. 

 ( South, 



South. 



Situation of the compass by which 

 the Sun's azimuth [col. vi.] was 

 observed. 



Starboard side of the main deck. 

 Larboard ditto. 

 Centre of main hatches. 



( On the binnacle amidships of the 

 I quarter-deck, 10 ft. from taffrail. 



"k Compass on a stand on the middle 

 V of the quarter-deck, 6 feet abaft 

 ) capstern spindle. 



Starboard side of the main deck. 



Larboard side of the main deck. 



On the binnacle, 10 ft. from taffrail, 



Ditto. 



Ditto. 



Starboard side of the main deck. 



Larboard ditto. 



Starboard side of the main deck. 



Larboard ditto. 



Centre of main hatches. 



Centre of fore hatches. 



Larboard side of the fore-castle near 



the windlass end. 

 Starboard ditto. 



The azimuths contained in the above Table, [col, VI.] were taken, either by the needle of a theodolite, or by a compass fitted up at sea for the purpose, with a card made ex- 

 tremely light, and a bar fastened edgewise to it by two brass screws, as represented in Plate II. fig. 4. The compass being small, the card light, and the needle very powerful, owing 

 to the thickness of its ends, it performed incomparably better than an expensive azimuth compass of larger dimensions, which, indeed, was so sluggish and erroneous in its indications, 

 that I could make no good use of it. I prefer a needle on its edge to one with broad flat ends of the usual form, because it must fix itself more accurately and certainly in the magnetic 

 meridian. A broad flat needle, on the other hand, by having its ends iU temiiered, may have the two poles at the two opposite corners, so that the magnetic axis may run diagonally. 

 In this case, the middle of the bar may point 2 or 3 degrees or more, to the east or west of its proper position. The directive property of a horizontal magnetical needle being extremely 

 small, in very high latitudes, it is of essential importance for the quick traversing of a compass, that the card and needle be as hght as possible ; for, in proportion as the weight of the 

 card with its appendages is diminished, the friction on the point on which it traverses must be less. Hence, as the power of a magnet depends, probably, more on the extent of the sur- 

 face of its ends than on its weight, I mean to prepare a compass for future observations with a hollow needle. 



