Hansteen, from whom he received the apparatus, has now given permission to Captain Fitz-Roy to publish them with his own. I have already noticed the great loss of magnetism which took place in this cylinder during Captain King"s voyage, and the care with which that officer availed himself of every opportunity of ascertaining, by direct observation, 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 repeating 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 Rio 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. Hansteen, 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 stations 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 differences of dip existing in different localities at the same station.
{516}
DIPS, _observed by_ Capt. P. P. King, 1826 to 1831.
+------------------+-------+---------------------+---------------------+Marked end a N. Pole.Marked end a S. Pole.----------+----------+----------+----------+Station.Needle.aa"a"a""+------------------+-------+----------+----------+----------+----------+""""Rio de Janeiro {115 58,513 02,415 05,713 18,0{214 39,412 30,414 49,013 07,3{122 54,124 04,721 55,622 46,0Sta. Catharina {223 22,820 32,323 34,221 00,7{321 17,821 08,523 26,222 57,2{136 48,437 49,335 25,437 26,9Monte Video {237 17,234 53,837 17,134 37,4{336 36,135 10,337 12,436 13,2{164 41,752 42,665 51,254 54,0Port Famine {260 41,959 32,260 32,159 33,6{360 03,958 43,460 35,559 37,5{141 09,930 50,941 04,631 32,6Gorriti {236 29,233 26,435 17,134 02,7{334 52,334 18,536 06,935 01,3Sea Bear Bay158 26,547 53,860 34,847 53,4{165 24,754 23,865 47,754 43,6St. Martin Cove {260 25,659 28,359 49,958 48,6{359 48,958 40,760 43,459 53,3{154 23,945 38,356 19,245 11,1Chiloe {250 24,049 12,950 28,448 29,6{349 43,948 48,351 24,550 02,2{143 04,533 59,944 38,834 54,6Valparaiso {240 48,240 49,740 53,741 09,7{340 54,940 45,440 49,841 16,7{150 22,739 16,051 08,240 03,2Juan Fernandez {244 19,345 57,643 45,846 13,7{345 50,445 07,944 34,843 25,7Talcahuano----------+------------------+-------+----------+----------+----------+----------+
+------------------+---------------------+-------------------------+Station.Dip deduced.Remarks.+------------------+---------------------+-------------------------+" "Rio de Janeiro {14 16,2 } 14 00,1 S.{13 44,1 }{22 49,6 }Sta. Catharina {22 03,6 } 22 12,4 S.{21 44,0 }{37 00,7 }Monte Video {35 59,3 } 36 28,4 S.{36 25,3 }{59 44,9 }Port Famine {60 04,5 } 59 52,6 S.{59 48,5 }{35 38,3 }Gorriti {34 43,8 } 35 05,9 S.{34 55,6 }Sea Bear Bay53 13,5 53 13,5 S.{59 46,4 }St. Martin Cove {59 38,4 } 59 43,8 S.{59 46,6 }{49 59,4 }Chiloe {49 38,7 } 49 52,6 S.{49 59,7 }{38 40,1 }Valparaiso {40 55,4 } 40 10,7 S.{40 56,7 }{44 40,5 }Juan Fernandez {45 04,6 } 53 13,5 S.{44 44,7 }Talcahuano-- 45 10,0 S.The particulars of thisobservation are wanting.+------------------+---------------------+-------------------------+
{517}
The following TABLE contains Captain KING"S Observations of Intensity, with the times of vibration corrected for the arc and reduced to a standard temperature of 60.
MAGNETIC INTENSITY, _observed by_ Capt. P. P. King _between 1826 and 1831._
----------------+------------+------+------+-----------+-----------------CorrectedStation.Date.Time.Therm.Time.Particular place.
----------------+------------+------+------+-----------+-----------------s.Greenwich {1826 Mar. 22734,4555,0733,97 }Observatory.
{1831 Jan. 24775,8041,6776,01 }Madeira1826 May 31628,6866,0627,79Consul"s Garden.
Teneriffe-- June 12607,9675,0606,73Fort St. Pedro.
Port Praya {-- -- 22559,5381,5} 557,08 {Landing Place, {-- -- 24557,5885,0} {Quail Island.
{-- Aug. 29546,3677,0545,16 }{1827 Sept.12552,0675,5}Rio de Janeiro {-- -- 15552,9580,0} }Rat Island.
{-- -- 15553,7383,0} 551,70 }{-- -- 15553,4885,0} }{1828 Dec. 21562,5584,0561,05 }Sta Catharina1827 Nov. 3554,4267,5553,58Anhatomirim.
{1826 Oct. 29550,6863,0} 549,44 }Gorriti {-- Nov. 6549,6366,0} }The Well.
{1829 Jan. 10564,1280,0562,78 }{1827 Dec. 18555,1278,3553,87 }South point near Monte Video {1828 Oct. 8562,0072,5560,95 }the sea.
{1830 June 1565,4159,0564,89 }Port Sta Elena1826 Dec. 4557,2668,0556,42Landing-place.
Sea Bear Bay1829 Mar. 20577,3670,0576,37Landing-place.
{1827 Jan. 15584,8856,0}St. Martin Cove{-- -- 15583,4858,0} 584,29 }Head of the {-- -- 22585,8255,0} }Cove.
{-- Mar. 27585,8264,0585,08 }{1828 Jan. 28589,7555,0589,36 }{-- May 8596,4943,8596,54 }Port Famine {-- June 18595,8632,7} 595,81 }Observatory.
{-- July 30594,8536,2} }{1830 Apr. 30598,9545,0598,97 }Chiloe {1829 Sept. 1565,4054,0} 565,23San Carlos.
{-- Dec. 15565,6953,0}Juan Fernandez1830 Feb. 19552,7770,0551,83Landing-place.
Talcahuano {1829 Dec. 18556,4267,0555,59 }Fort Galvez.
{1830 May 12557,1860,5557,18 }{1829 Aug. 4549,1059,0548,59 }Valparaiso {1830 Jan. 11551,7777,0} 551,60 }Almendral.
{-- Feb. 1553,5068,5} }----------------+------------+------+------+-----------+-----------------
{518}
At Rio de Janeiro, which was the first station observed at in South America, the cylinder was vibrated in August 1826, September 1827, and December 1828; in the intervals between these dates are comprised the greater part of the observations on the east side of South America. There is no direct observation at Rio subsequently to December 1828; but we are enabled to supply the time of vibration, which would have been observed had the cylinder been employed at Rio on June 1, 1830, in the following manner.
We have seen that on the 15th September 1827 the time of vibration was observed at Rio; on the 18th December following it was observed at Monte Video. These observations give the intensity at Monte Video relatively to that at Rio, subject to whatever change of magnetism the cylinder may have undergone in the interval of three months. This comparison was repeated in the following year, on Captain King"s return from Monte Video to Rio, the interval being nearly of the same duration, and the order of the experiment reversed, the pa.s.sage being in this instance from Monte Video to Rio, it having been before from Rio to Monte Video. On the supposition of an uniform, or nearly uniform rate of change in the cylinder, the errors arising therefrom during the two pa.s.sages would be of opposite kinds, and should compensate each other in a mean of the two comparisons. Calling the force at Rio unity, these comparisons give its value at Monte Video respectively as follows, namely,
September and December 1827 ... 1.197 } October and December 1828 ... 1.207 } Mean 1.202.
On the 1st of June 1830, being then on his return from the west coast of South America, and on the eve of sailing for England, Captain King again observed the time of vibration of the cylinder at Monte Video; whence, through the preceding comparison, we obtain the time of vibration at Rio, which should belong to the same date. We have thus a fourth date at Rio, which, added to those enumerated above, will include the whole of the South American stations; and we have only to distribute in each interval the loss of magnetism which the observations shew to have taken place from one date to the next, in the manner which may appear most suitable. There is no very obvious indication that the loss was other than gradual; and by considering it uniform in each separate {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 vibration 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 resulting 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 general body of results of other observers, the values of his 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 determinations by the following observers, namely,
1817 and 1820 Freycinet 0,890 } 1827 Lutke 0,886 } 0,884 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. I have {520} deducted, from my determination of the dip, 12" for the probable change between 1822 and 1826. At Teneriffe the dip has been frequently observed; but the values a.s.signed by different observers vary so much as to indicate a more than usual frequency of local disturbance, which might also be expected from the geological character of that island. It would be unsafe therefore to employ any dip for that station but one which was certainly obtained at the same spot at which the horizontal intensity was observed.
The dates of the observations at these three stations fall between the observations at Greenwich in March 1826, and those at Rio de Janeiro in August of the same year. Having the intensity at Greenwich = 1,372 and at Rio = 0,884, and the dip at Greenwich 69 52", and at Rio 14 00, we have the time of vibration of Captain King"s cylinder as a dipping needle at Rio at the respective dates as follows, namely,
March 1826 536,2.
August 1826 537,0.
It appears therefore that but a very slight change took place in the magnetism of the cylinder during the outward voyage, and we may take 536,6 as the time of vibration at Rio, corresponding to the dates of the intermediate observations; and this is done in the table for Madeira and Port Praya. {521}
TABLE I.
------------------+------------------------+---------+-----+---------Time of Vibration.-----------+------------+Rio de Janeiro.Horizontal.As a DippingInterval.Loss.Per Diem.
Needle.------------------+-----------+------------+---------+-----+---------s.s.Days.s.August 29, 1826545,2537,0} 3826,5.017 September 15, 1827551,7543,5}December 21, 1828561,1552,74629,2.020 June 1, 1830563,8555,45272,7.005 ------------------+-----------+------------+---------+-----+---------
TABLE II.
---------------+-------------+------------------------+------------------Time of Vibration.Intensity.
------------------------+-----------+------At the Station.At Rio.--------+-------+-------+As aAs aDippingDippingRio= Station.Date.Horizon.Needle.Needle.Rio=1,000.0,884.
---------------+-------------+--------+-------+-------+-----------+------s.s.s.Madeira1826 May 31627,79430,1536,61,5561,377Port Praya {1826 June 22}557,08465,4536,61,3301,177 {and 24}Sta Catharina1827 Nov. 3553,58532,7544,51,0450,920Gorriti {1826 Oct. 29}549,44497,0538,11,172}-- {and Nov. 6}}1,1751,041 --1829 Jan. 10562,78509,0552,81,179}Monte Video1827 Dec. 18553,87496,7545,41,206}--1828 Oct. 8560,95503,0551,31,201}1,2031,065 --1830 June 1564,89506,6555,41,202}Sea Bear Bay1829 Mar. 20576,37446,0553,11,5381,361St. Martin {1827 Jan. 15}584,29414,9539,41,691}Cove {and 22}}1,6921,498 ---- Mar. 27585,08415,4540,61,694}Port Famine1828 Jan. 28589,36417,5546,21,712---- May 8596,54422,6548,21,683}-- {-- June 18}595,81422,1549,31,694}1,7001,505 {and July 30}}--1830 April 26598,97424,3555,11,712}Chiloe {1829 Sept. 1}565,23453,7554,21,4021,321 {and Dec. 15}Juan Fernandez1830 Feb. 19551,83464,7554,81,4251,262Talcahuano1829 Dec. 18555,59466,5554,61,413}1,4121,250 --1830 May 12557,18467,4555,31,412}Valparaiso1829 Aug. 4548,59479,5553,91,334}1,3291,176 -- {1830 Jan. 11}551,60482,1554,61,324}{and Feb. 1}---------------+-------------+--------+-------+-------+-----------+------
{522}
4.--The following Table exhibits the MAGNETIC OBSERVATIONS of Captains King and Fitz-Roy collected in one view.
---------------+---------+----------+----------+--------------+----------Intensity,Paris= Stations.Lat.i.tude.Longitude.Variation.Dip.1,348.
---------------+---------+----------+----------+--------------+----------""""Madeira32 38 N.16 56 W.--K. 1,377Terceira38 39 N.27 13 W.24 18 W.F. 68 06 N.F. 1,457{ --K. 1,177 Port Praya14 54 N.23 30 W.16 30 W.{F. 46 20,2 N.F. 1,154{F. 45 46,5 N.F. 1,157Ascension7 56 S.14 24 W.13 30 W.F. 1 39,2 N.F. 0,873St. Helena15 55 S.5 43 W.18 00 W.F. 18 01,2 S.{F. 0,822{F. 0,850Falkland51 32 S.58 07 W.19 00 E.{F. 53 30,4 S.F. 1,349 Islands{F. 53 19,6 S.F. 1,385Pernambuco8 04 S.34 51 W.5 54 W.F. 13 12,9 N.F. 0,914Bahia12 59 S.38 30 W.4 18 W.{F. 4 55,8 N.}F. 0,871{F. 5 53,5 N.}Rio de Janeiro22 55 S.43 09 W.2 00 E.{K. 14 00,1 S.}F. 0,878{F. 13 37,4 S.}Sta Catharina27 26 S.48 33 W.--K. 22 12,4 S.K. 0,920Gorriti34 57 S.54 57 W.--K. 35 05,9 S.K. 1,041Monte Video34 53 S.56 13 W.12 00 E.{K. 36 28,4 S.K. 1,065{F. 34 51,2 S.F. 1,055Blanco Bay38 57 S.61 59 W.15 00 E.F. 41 54,0 S.F. 1,113Port Desire47 45 S.65 55 W.20 12 E.F. 52 43,5 S.F. 1,359Sea Bear Bay47 51 S.65 48 W.--K. 53 13,5 S.K. 1,361R. Santa Cruz50 07 S.68 24 W.20 54 E.F. 55 15,7 S.F. 1,425St. Martin Cove55 51 S.67 34 W.--K. 59 43,8 S.K. 1,498Port Famine53 38 S.70 58 W.23 00 E.K. 59 52,6 S.{K. 1,505{F. 1,560Port San Andres46 35 S.75 35 W.20 48 E.F. 54 13,6 S.--Port Low43 48 S.74 02 W.19 48 E.F. 51 20,1 S.F. 1,326Chiloe41 51 S.73 56 W.18 00 E.{K. 49 52,6 S.K. 1,321{F. 48 58,9 S.F. 1,304Valdivia39 53 S.73 29 W.17 30 E.F. 46 46,5 S.F. 1,238Concepcion36 42 S.73 10 W.16 48 E.{K. 45 10,0 S.K. 1,250{F. 43 15,4 S.F. 1,186Valparaiso33 02 S.71 41 W.15 18 E.{K. 40 10,7 S.}K. 1,176{F. 38 03,1 S.}Coquimbo29 59 S.71 26 W.14 24 E.--F. 1,111Callao12 04 S.74 14 W.10 00 E.F. 7 02,8 S.Galapagos0 50 S.89 37 W.9 30 E.F. 8 41,2 N.IslandsDitto0 15 S.90 31 W.9 30 E.F. 9 28,6 N.F. 1,069Juan Fernandez33 38 S.78 53 W.K. 44 49,8 S.K. 1,262Otaheite17 29 S.149 30 W.7 54 E.F. 30 13,5 S.F. 1,017Cape of Good34 11 S.18 26 E.28 30 W.F. 52 35,0 S.F. 1,014 HopeMauritius20 09 S.57 31 E.11 18 W.F. 54 00,8 S.F. 1,192Keeling Islands12 05 S.96 55 E.1 12 W.F. 38 33,1 S.New Zealand35 16 S.174 00 E.14 00 E.F. 59 32,0 S.F. 1,591King George35 02 S.117 56 E.5 36 W.F. 64 41,3 S.F. 1,709 SoundHobart Town42 53 S.147 24 E.11 06 E.F. 70 34,9 S.F. 1,817Sydney33 51 S.151 17 E.10 24 E.F. 62 49,4 S.F. 1,685 ---------------+---------+----------+----------+--------------+----------
{523}
GENERAL REMARKS.
1. _Variation._
Captain Fitz-Roy"s observations are so well distributed over the southern hemisphere, that a good view of the changes which the variation is undergoing throughout its meridians may be obtained by comparing his determinations with those of earlier observers at the same stations. The following table has been formed for the purpose of exhibiting such a comparison at all those stations where materials for it exist; and I may here remark how much such comparisons are facilitated by the valuable collection of early observations contained in the Appendix to the Magnetismus der Erde.
CAPE OF GOOD HOPE.VALPARAISO.
Observer.Date.Variation.Observer.Date.Variation.
Davis16050. 30 E.Don G. Juan174412. 30 E.
Keeling16090. 12 W.Vancouver179314. 49 E.
Leydecker16758. 28 W.Lutke182715. 00 E.
Mathews172416. 22 W.Fitz-Roy183515. 18 E.
La Caille175219. 0 W.Wales177220. 26 W.CALLAO.
Wales177521. 14 W.Ulloa17409. 02 E.
Bligh178823. 16 W.Duperrey18239. 30 E.
Dentrecasteaux179224. 30 W.Fitz-Roy183510. 36 E.