MAGNETIC OBSERVATIONS. 



79 



As the series is a short one, I give the separate means of 6 and. of 7 days to 

 compare with the mean of 13; these partial results confirm the general regularity 

 of the diurnal variation, and show that we may place confidence in the resvilt 



Diurnal Variation of the Magnetic Declination at Port Fo 



ulke, Smith Strait, December to 









March, 1860-61. 







Mean looal 



Mean 



Mean 



Mean 



Mean 



Mean 



Mean 



Mean 



time. 



of 6 days. 



of 7 days. 



of 13 days. 



looal time. 



of 6 days. 



of 1 days. 



of 13 days. 



8 A. M. 



30°.63- 



270.46 



28°. 92 



8 P.M. 



30°.96 



27°.79 



290.26 



9 



X 30.49 



27.48 



28.87 



9 



31.02 



27.87 



29.32 



10 



30.57 



27.31 



28.81 



10 



31.07 



27.89 



29.36 



11 



80.66 



27.32 



28.86 



11 



31.06 



27.87 



29.34 



Noon 



30.76 



27.10 



28.79 



Midnight 



131.07 



28.00 



J 29.42 



1 



30.64 



X27.07 



X28.72 



1 



31.05 



27.96 



29.38 



2 



30.68 



27.08 



28.74 



2 



31.02 



27.92 



29.35 



3 



30.66 



24.25 



28.83 



3 



31.06 



128.01 



1 29.42 



4 



30.75 



24.34 



28.91 



4 



31.05 



27.83 



29.31 



5 



30.82 



27.44 



29.00 



5 



31.05 



27.80 



29.30 



6 



30.79 



27.62 



29.08 



6 



31.00 



27.67 



29.21 



7 



30.89 



27.76 



29.20 



7 



30.93 



27.61 



29.14 











8 



30.87 



27.50 



29.05 



West elongations are indicated by a , and east elongations by J. 



Taking the mean of the two values at 8 A. M., and subtracting each hourly value 

 from the mean of the whole (29°. 11), we obtain the diurnal variation as given in the 

 following table ; the values are given in minutes. For comparison I have added the 

 diurnal variation observed at Van Rensselaer Harbor by Dr. Kane ;^ these results 

 are given in two columns, the second one containing the variation after the omission 

 of the larger disturbances. To separate in our series the disturbances from the 

 regular readings would not lead to any satisfactory results, as the observations are 

 much too limited in number ; no very large disturbances, however, are recorded, so 

 that we may with equal advantage compare the Port Foulke results with others, 

 including or excluding the larger disturbances. By the additional comparisons with 

 Point Barrow,^ Toronto, and Philadelphia,' we may be enabled to generalize certain 

 features in the diurnal variation of the north-magnetic hemisphere. Van Eensselaer 

 and Port FouUte are stations situated to the northward of the magnetic pole (of dip 

 90° and horizontal force 0). 



> See my discussion of Dr. Kane's Magnetic Observations in the Arctic Seas, in the Smithsonian 

 Contributions to Knowledge, November, 1858. 



a Phil. Trans. Royal Society, 1857, Part II, Art. xxiv. On hourly observations of the magnetic 

 declination made by Captain R. Maguire, R. N., and the officers of H. M. S. Plover, in 1852-53-54, at 

 Point Barrow. By Maj.-Gcn. E. Sabine. 



The comparison with Toronto is taken from the same paper. 



3 Smithson''an Contributions to Knowledge, June, 1862. Discussion of the Magnetic and Meteoro- 

 logical Observations made at the Cfirard College, Philadelphia, 1840 to 1845, Part II. By A. D. 

 Bache, LL.D. 



