DTP AND INTENSITY. 



515 



3. Captain King's Observations of Dip and Intensitij, 



Captain King, having hitherto made known his observations 

 with the same cylinder in the years 1826 to 1830 only by com- 

 municating them to M. Hansteen, from whom he received the 

 apparatus, has now given permission to Captain P'itz-Roy to 

 publish them with his own. I have already noticed the great 

 loss of magnetism which took place in this cylinder during Cap- 

 tain King's voyage, and the care with which that officer availed 

 himself of every opportunity of ascertaining, by direct obser- 

 vation, the proportion of the loss sustained in separate portions of 

 the voyage. There are twelve stations of observation on the east 

 and west coasts of South America, besides three stations in ports 

 of the Atlantic on the outward voyage. By the practice of repeat- 

 ing observations at the same station at distant intervals, the South <^ 

 American stations are so linked together and connected, that by 

 adopting a method similar to that used in determining longitudes 

 by means of chronometers, we may compute the intensity at all 

 the South American stations referred to and dependent on the 

 force at Ptio de Janeiro ; regarding Rio in the same light as a first 

 meridian is considered in determinations of longitude. We may 

 then make Rio the means of connecting the whole series with 

 Europe ; for which it is remarkably well suited, the intensity there 

 having been determined, independently of Captain King, by 

 four observers of different nations, whose results are extremely 

 accordant. 



The dip observations of Captain King were communicated, in 

 occasional correspondence during the voyage, to M. Hansteeny 

 who computed them by Mayer's formula, and arranged them in 

 a table, of which a copy was given by Captain King to Captain 

 Fitz-Roy, and is printed in the next page. At some of the sta- 

 tions Captain Fitz-Roy also observed the dip in the subsequent 

 voyage, and, as will be seen, the results of the two observers 

 sometimes differ considerably. This may have been caused, either 

 by instrumental or other error of observation, or by actual differ- 

 ences of dip existing in different localities at the same station. 



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