Part 45
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.
a
a'
a"
a"'
+------------------+-------+----------+----------+----------+----------+
'
'
'
'
Rio de Janeiro {
1
15 58,5
13 02,4
15 05,7
13 18,0
{
2
14 39,4
12 30,4
14 49,0
13 07,3
{
1
22 54,1
24 04,7
21 55,6
22 46,0
Sta. Catharina {
2
23 22,8
20 32,3
23 34,2
21 00,7
{
3
21 17,8
21 08,5
23 26,2
22 57,2
{
1
36 48,4
37 49,3
35 25,4
37 26,9
Monte Video {
2
37 17,2
34 53,8
37 17,1
34 37,4
{
3
36 36,1
35 10,3
37 12,4
36 13,2
{
1
64 41,7
52 42,6
65 51,2
54 54,0
Port Famine {
2
60 41,9
59 32,2
60 32,1
59 33,6
{
3
60 03,9
58 43,4
60 35,5
59 37,5
{
1
41 09,9
30 50,9
41 04,6
31 32,6
Gorriti {
2
36 29,2
33 26,4
35 17,1
34 02,7
{
3
34 52,3
34 18,5
36 06,9
35 01,3
Sea Bear Bay
1
58 26,5
47 53,8
60 34,8
47 53,4
{
1
65 24,7
54 23,8
65 47,7
54 43,6
St. Martin Cove {
2
60 25,6
59 28,3
59 49,9
58 48,6
{
3
59 48,9
58 40,7
60 43,4
59 53,3
{
1
54 23,9
45 38,3
56 19,2
45 11,1
Chiloe {
2
50 24,0
49 12,9
50 28,4
48 29,6
{
3
49 43,9
48 48,3
51 24,5
50 02,2
{
1
43 04,5
33 59,9
44 38,8
34 54,6
Valparaiso {
2
40 48,2
40 49,7
40 53,7
41 09,7
{
3
40 54,9
40 45,4
40 49,8
41 16,7
{
1
50 22,7
39 16,0
51 08,2
40 03,2
Juan Fernandez {
2
44 19,3
45 57,6
43 45,8
46 13,7
{
3
45 50,4
45 07,9
44 34,8
43 25,7
Talcahuano
--
--
--
--
--
+------------------+-------+----------+----------+----------+----------+
+------------------+---------------------+-------------------------+
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 Bay
53 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 this
observation 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._
----------------+------------+------+------+-----------+-----------------
Corrected
Station.
Date.
Time.
Therm.
Time.
Particular place.
----------------+------------+------+------+-----------+-----------------
s.
Greenwich {
1826 Mar. 22
734,45
55,0
733,97 }
Observatory.
{
1831 Jan. 24
775,80
41,6
776,01 }
Madeira
1826 May 31
628,68
66,0
627,79
Consul's Garden.
Teneriffe
-- June 12
607,96
75,0
606,73
Fort St. Pedro.
Port Praya {
-- -- 22
559,53
81,5
} 557,08 {
Landing Place, {
-- -- 24
557,58
85,0
} {
Quail Island.
{
-- Aug. 29
546,36
77,0
545,16 }
{
1827 Sept.12
552,06
75,5
}
Rio de Janeiro {
-- -- 15
552,95
80,0
} }
Rat Island.
{
-- -- 15
553,73
83,0
} 551,70 }
{
-- -- 15
553,48
85,0
} }
{
1828 Dec. 21
562,55
84,0
561,05 }
Sta Catharina
1827 Nov. 3
554,42
67,5
553,58
Anhatomirim.
{
1826 Oct. 29
550,68
63,0
} 549,44 }
Gorriti {
-- Nov. 6
549,63
66,0
} }
The Well.
{
1829 Jan. 10
564,12
80,0
562,78 }
{
1827 Dec. 18
555,12
78,3
553,87 }
South point near Monte Video {
1828 Oct. 8
562,00
72,5
560,95 }
the sea.
{
1830 June 1
565,41
59,0
564,89 }
Port Sta Elena
1826 Dec. 4
557,26
68,0
556,42
Landing-place.
Sea Bear Bay
1829 Mar. 20
577,36
70,0
576,37
Landing-place.
{
1827 Jan. 15
584,88
56,0
}
St. Martin Cove{
-- -- 15
583,48
58,0
} 584,29 }
Head of the {
-- -- 22
585,82
55,0
} }
Cove.
{
-- Mar. 27
585,82
64,0
585,08 }
{
1828 Jan. 28
589,75
55,0
589,36 }
{
-- May 8
596,49
43,8
596,54 }
Port Famine {
-- June 18
595,86
32,7
} 595,81 }
Observatory.
{
-- July 30
594,85
36,2
} }
{
1830 Apr. 30
598,95
45,0
598,97 }
Chiloe {
1829 Sept. 1
565,40
54,0
} 565,23
San Carlos.
{
-- Dec. 15
565,69
53,0
}
Juan Fernandez
1830 Feb. 19
552,77
70,0
551,83
Landing-place.
Talcahuano {
1829 Dec. 18
556,42
67,0
555,59 }
Fort Galvez.
{
1830 May 12
557,18
60,5
557,18 }
{
1829 Aug. 4
549,10
59,0
548,59 }
Valparaiso {
1830 Jan. 11
551,77
77,0
} 551,60 }
Almendral.
{
-- Feb. 1
553,50
68,5
} }
----------------+------------+------+------+-----------+-----------------
{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 Dipping
Interval.
Loss.
Per Diem.
Needle.
------------------+-----------+------------+---------+-----+---------
s.
s.
Days.
s.
August 29, 1826
545,2
537,0
} 382
6,5
.017 September 15, 1827
551,7
543,5
}
December 21, 1828
561,1
552,7
462
9,2
.020 June 1, 1830
563,8
555,4
527
2,7
.005 ------------------+-----------+------------+---------+-----+---------
TABLE II.
---------------+-------------+------------------------+------------------
Time of Vibration.
Intensity.
------------------------+-----------+------
At the Station.
At Rio.
--------+-------+-------+
As a
As a
Dipping
Dipping
Rio= Station.
Date.
Horizon.
Needle.
Needle.
Rio=1,000.
0,884.
---------------+-------------+--------+-------+-------+-----------+------
s.
s.
s.
Madeira
1826 May 31
627,79
430,1
536,6
1,556
1,377
Port Praya {
1826 June 22
}557,08
465,4
536,6
1,330
1,177 {
and 24
}
Sta Catharina
1827 Nov. 3
553,58
532,7
544,5
1,045
0,920
Gorriti {
1826 Oct. 29
}549,44
497,0
538,1
1,172}
-- {
and Nov. 6
}
}1,175
1,041 --
1829 Jan. 10
562,78
509,0
552,8
1,179}
Monte Video
1827 Dec. 18
553,87
496,7
545,4
1,206}
--
1828 Oct. 8
560,95
503,0
551,3
1,201}1,203
1,065 --
1830 June 1
564,89
506,6
555,4
1,202}
Sea Bear Bay
1829 Mar. 20
576,37
446,0
553,1
1,538
1,361
St. Martin {
1827 Jan. 15
}584,29
414,9
539,4
1,691}
Cove {
and 22
}
}1,692
1,498 --
-- Mar. 27
585,08
415,4
540,6
1,694}
Port Famine
1828 Jan. 28
589,36
417,5
546,2
1,712
--
-- May 8
596,54
422,6
548,2
1,683}
-- {
-- June 18
}595,81
422,1
549,3
1,694}1,700
1,505 {
and July 30
}
}
--
1830 April 26
598,97
424,3
555,1
1,712}
Chiloe {
1829 Sept. 1
}565,23
453,7
554,2
1,402
1,321 {
and Dec. 15
}
Juan Fernandez
1830 Feb. 19
551,83
464,7
554,8
1,425
1,262
Talcahuano
1829 Dec. 18
555,59
466,5
554,6
1,413}1,412
1,250 --
1830 May 12
557,18
467,4
555,3
1,412}
Valparaiso
1829 Aug. 4
548,59
479,5
553,9
1,334}1,329
1,176 -- {
1830 Jan. 11
}551,60
482,1
554,6
1,324}
{
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.
---------------+---------+----------+----------+--------------+----------
'
'
'
'
Madeira
32 38 N.
16 56 W.
--
K. 1,377
Terceira
38 39 N.
27 13 W.
24 18 W.
F. 68 06 N.
F. 1,457
{ --
K. 1,177 Port Praya
14 54 N.
23 30 W.
16 30 W.
{F. 46 20,2 N.
F. 1,154
{F. 45 46,5 N.
F. 1,157
Ascension
7 56 S.
14 24 W.
13 30 W.
F. 1 39,2 N.
F. 0,873
St. Helena
15 55 S.
5 43 W.
18 00 W.
F. 18 01,2 S.
{F. 0,822
{F. 0,850
Falkland
51 32 S.
58 07 W.
19 00 E.
{F. 53 30,4 S.
F. 1,349 Islands
{F. 53 19,6 S.
F. 1,385
Pernambuco
8 04 S.
34 51 W.
5 54 W.
F. 13 12,9 N.
F. 0,914
Bahia
12 59 S.
38 30 W.
4 18 W.
{F. 4 55,8 N.
}F. 0,871
{F. 5 53,5 N.
}
Rio de Janeiro
22 55 S.
43 09 W.
2 00 E.
{K. 14 00,1 S.
}F. 0,878
{F. 13 37,4 S.
}
Sta Catharina
27 26 S.
48 33 W.
--
K. 22 12,4 S.
K. 0,920
Gorriti
34 57 S.
54 57 W.
--
K. 35 05,9 S.
K. 1,041
Monte Video
34 53 S.
56 13 W.
12 00 E.
{K. 36 28,4 S.
K. 1,065
{F. 34 51,2 S.
F. 1,055
Blanco Bay
38 57 S.
61 59 W.
15 00 E.
F. 41 54,0 S.
F. 1,113
Port Desire
47 45 S.
65 55 W.
20 12 E.
F. 52 43,5 S.
F. 1,359
Sea Bear Bay
47 51 S.
65 48 W.
--
K. 53 13,5 S.
K. 1,361
R. Santa Cruz
50 07 S.
68 24 W.
20 54 E.
F. 55 15,7 S.
F. 1,425
St. Martin Cove
55 51 S.
67 34 W.
--
K. 59 43,8 S.
K. 1,498
Port Famine
53 38 S.
70 58 W.
23 00 E.
K. 59 52,6 S.
{K. 1,505
{F. 1,560
Port San Andres
46 35 S.
75 35 W.
20 48 E.
F. 54 13,6 S.
--
Port Low
43 48 S.
74 02 W.
19 48 E.
F. 51 20,1 S.
F. 1,326
Chiloe
41 51 S.
73 56 W.
18 00 E.
{K. 49 52,6 S.
K. 1,321
{F. 48 58,9 S.
F. 1,304
Valdivia
39 53 S.
73 29 W.
17 30 E.
F. 46 46,5 S.
F. 1,238
Concepcion
36 42 S.
73 10 W.
16 48 E.
{K. 45 10,0 S.
K. 1,250
{F. 43 15,4 S.
F. 1,186
Valparaiso
33 02 S.
71 41 W.
15 18 E.
{K. 40 10,7 S.
}K. 1,176
{F. 38 03,1 S.
}
Coquimbo
29 59 S.
71 26 W.
14 24 E.
--
F. 1,111
Callao
12 04 S.
74 14 W.
10 00 E.
F. 7 02,8 S.
Galapagos
0 50 S.
89 37 W.
9 30 E.
F. 8 41,2 N.
Islands
Ditto
0 15 S.
90 31 W.
9 30 E.
F. 9 28,6 N.
F. 1,069
Juan Fernandez
33 38 S.
78 53 W.
K. 44 49,8 S.
K. 1,262
Otaheite
17 29 S.
149 30 W.
7 54 E.
F. 30 13,5 S.
F. 1,017
Cape of Good
34 11 S.
18 26 E.
28 30 W.
F. 52 35,0 S.
F. 1,014 Hope
Mauritius
20 09 S.
57 31 E.
11 18 W.
F. 54 00,8 S.
F. 1,192
Keeling Islands
12 05 S.
96 55 E.
1 12 W.
F. 38 33,1 S.
New Zealand
35 16 S.
174 00 E.
14 00 E.
F. 59 32,0 S.
F. 1,591
King George
35 02 S.
117 56 E.
5 36 W.
F. 64 41,3 S.
F. 1,709 Sound
Hobart Town
42 53 S.
147 24 E.
11 06 E.
F. 70 34,9 S.
F. 1,817
Sydney
33 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.
Davis
1605
0. 30 E.
Don G. Juan
1744
12. 30 E.
Keeling
1609
0. 12 W.
Vancouver
1793
14. 49 E.
Leydecker
1675
8. 28 W.
Lutke
1827
15. 00 E.
Mathews
1724
16. 22 W.
Fitz-Roy
1835
15. 18 E.
La Caille
1752
19. 0 W.
Wales
1772
20. 26 W.
CALLAO.
Wales
1775
21. 14 W.
Ulloa
1740
9. 02 E.
Bligh
1788
23. 16 W.
Duperrey
1823
9. 30 E.
Dentrecasteaux
1792
24. 30 W.
Fitz-Roy
1835
10. 36 E.
