320 L. A. Bauer— Variation of Terrestrial Magnetism. 
uniformly along the equator in a westward direction! Jf the 
motion continues at the same rate around the equator, then 
the west agonic will accomplish a complete revolution in 
3609 = 1580 years, the east agonic in .289 = 2590 years! The 
average annual motion of the two agonies is 0°-194, and the 
average period of revolution Gf the agonics revolve around 
the equator) about 2000 years. 
Longitudes of Intersections of Agonic Lines with the Equator. 
West Agonic. East Agonic. 
Date. Authority. eat ah 
S Obs’d. | Comp.) O.-C.) Obs’d. | Comp. | O0.-C. 
1540 |W. van Bemmelen* -____- —23t++ | —20°1; —3 |—100 —126°1} —26 
1580 Par Tae Peart 17 —11°0} —6 | __: —120°5) _. 
1600 Te at, bheeeey — 8 — 64) —2 |—116 —117'8| + 2 
1610 |C. Hansteen} --...-...-.,—13 |— 4:1) —9 '—118 —116°4, — 2 
1640 |W. van Bemmelen* ____.|— 2 OP — onl ane —112°2) — 5 
1665 SHR, Contt eee + 9 + 84 +1 |—126 |—108°7| —17 
1680 Se AULA Fae +175 |+11°8) +6 —112 —106°6 — 6 
O05 | Hr Halley) coe See ee ae +175 (+164 41 |—118 —103°8, —14 
1710 |C. Hansteent -....------ +22°5 |+18°7 +4 |—119 —102°5| —16 
1720 ie BP VW ss en ie -| +26 +21°0) +5 | __- 100 
1730 peng wil SAPs Sap Meera hb +28 +23°2) +5 |— 98 — 99°77 + 7 
1744 “AAT Te: (EERE 2 eee i+ 31 +264 +5 |—105tt{ |— 97-7) — 7 
1756 Sars ea aeRO onc +31 +29°2) +2 |— 97ttt |— 96:1) — 1 
1770 PSE) ces eae +39 +382°4 +7 |— 99ttt |— 94:1) — 5 
1780 mC ma ee ene feet oo +346 +4 |—100ttt |— 92°7) — 7 
1787 O60 oak thea es BOE EN +40 +386°2) +4 |—101t{¢ |— 91:8) — 9 
1800 Beth lithe Meck eae 0 +43 + 39°2) +4 |—100 — 90:0) —10 
TSE a. Neates|| terete _..| +42 +43°1) —1 |— 77 — 876) +11 
1627 AY tina ooo oe eee +53 +45°4, +8 |— 75 — 86:2) +11 
1829 |Erman & Petersen{ ____ | +50 +45°8) +4 |— 74 — 85:9) +12 
1885.) 2. Barlow f i-* 94-5 Sees +43°5 |+46°7 —3 |— 75 — 85:4 +10 
1840 |E. Sabinett+.--....-.--..|+49 | |+48°3) +1 |—105 — 844 —21 
1850 CAS Schotitis so sete ce +49°5 (+50.6) —1 | -_- — 83:0; _- 
1858 | British Admiralty|||| ----- +50°5 |+52°4) —2 |— 80 — 81:9) + 2 
1872 be Bia Gs Soot +54 +55°6 —2 |\— 745 |— 79°9) + 5 
1875 1. A. Schott se. +62.5 |4+56°3) —4) -_- — (OD ge ae 
1880 | British Admiralty99 .-.| +55 +574 —2 |— 79°35 |— 78:8) — 1 
L885 |G. Neumayert=*_— 2... _ = +54°2 |+58°6) —4 !— 80 -- 781) — 2 
* De Isogonen in de XVI%* en XVII*¢e Eeuw, Utrecht, 1893; values are 
preliminary, according to the author. 
+ Untersuchungen uber den Magnetismus der Erde, Christiania, 1819, Atlas. 
t Halley’s Equal Variation Chart in Greenwich Observations for 1869, or in 
‘“‘Neudrucke von Schriften und Karten tiber Meteorologie und Erdmagnetismus,” 
No. 4, Hellmann, Berlin, 1894. 
|| Thomas Yeates’ Equal Variation Chart for 1817; made use of copy in Brit- 
ish Museum. : 
§ Erman’s isogonic chart in Berghaus’ Physikalischer Atlas, 1st edition, 1845. 
4, ‘‘ Grundlagen der Gaussichen Theorie,” etc., Berlin, 1874. 
** Barlow’s isogonic chart in Phil. Trans., 1833. 
++ Sabine’s isogonic chart, 1840; used copy in “ Treatise upon Terrestrial Mag- 
netism,” London, 1871. 
¢ Bulletin No. 6, U. 8. Coast and Geodetic Survey. 
if Used reduced copy in Neumayer’s Atlas des Erdmagnetismus, Gotha, 1891. 
S§ Used reduced copies in Admiralty Manual for Deviations of the Compass, 
German edition, Vienna, 1873, and London edition, 1874. 
“[4{ Isogonie chart in Report of Challenger Expedition, Vol. II. Combined 
the result from this chart with that from Neumayer’s chart for 1880. 
*** Neumayer’s Atlas des Erdmagnetismus. 
tt} East longitude. minus; west longitude, plus. 
tt} Mean of several intersections. 
