OESERVATIONS OF 1KTE>^SITY. 



519 



interval, the results are found extremely accordant at several other 

 stations at which observations were repeated at distant intervals. 



In the first of the subjoined tables are given the times of vibra- 

 tion at Rio at the four periods referred to ; and the corresponding 

 times as a dipping needle. In its three last columns are shewn, — 

 the number of days comprised in each interval, — the increase in the 

 time of vibration owing to the loss of magnetism, — and the result- 

 ing daily correction, on the supposition in each case of the loss 

 having been uniform in the interval during which it occurred. 



The second table contains the corrected times of horizontal 

 vibration at each of the South American stations, at the dates 

 respectively inserted, — the corresponding times as a dipping- 

 needle, — the times of vibration as a dipping needle at Rio de 

 Janeiro at the same dates, derived from the observations in the 

 first table, — and the resulting intensity at each station relatively to 

 unity at Rio. Thus far the results are derived from Captain King^s 

 observations, unmixed with those of any other observer : but in 

 order to bring Captain King's series into connexion with the gene- 

 ral body of results of other observers, the values of liis intensities 

 are expressed in the final column in terms of the scale in common 

 use, in which the force at Paris = 1,348, and at Rio de Janeiro 

 0,884 ; the latter being the mean of four independent determi- 

 nations by the following observers, namely, 



0,884 



1817 and 1820 Freycinet 0,890 



1827 Liitke 0,886 



1830 Erman 0,879 



1836 Fitz-Roy 0,878 



Port St. Elena is not included in this table, as no dip was observed 

 there, and the total intensity consequently cannot be computed. 

 The three stations, Madeira, Teneriffe, and Port Praya, at which 

 the cylinder was vibrated in the outward voyage, are also without 

 dips observed by Captain King. The deficiency at Port Praya has 

 been supplied from Captain Fitz-Roy's observations and my own, 

 both having been made at the same place at which Captain King's 

 intensity was observed,— -Captain Fitz-Roy's at a later, and mine at 

 an earlier date. At Madeira also the dip has been supplied from 

 my observations, which were made in the British consul's garden 

 at Funchal, where Captain King's cylinder was vibrated. 1 have 



