198 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



covery of a copy in the British Museum in 1895 has thus far come 

 to light. Yet this particular chart, termed by me the "Atlantic 

 Chart," to distinguish it from the later one — the "World Chart" — 

 IS especially interesting, as it contains the routes followed by the 

 Pararnour Pink. Airy, when he reproduced Halley's " World Chart " 

 in the Greenwich observations of 1869, was seemingly not aware of 

 the "Atlantic Chart." ^ (See pi. 2.) 



The only description of Halley's chart by himself, thus far found, 

 is that either attached to certain editions of the chart or contained 

 on an accompanying leaflet. This, however, is very brief, and was 

 chiefly intended to instruct mariners in the use of the chart. Halley 

 points out that in certain regions where the " Curves " run suitably 

 they may be used "to estimate the Longitude at Sea thereby." To 

 his lines of equal " magnetic variation " he gave no distinctive name, 

 simply referring to them as the " Curve Lines." Thus he says : " What 

 is here properly New is the Curve Lines drawn over the several Seas 

 to show the degrees of the Variation of the Magnetical Needle or Sea 

 Compass." He doesj however, use the term " Line of No Variation." 

 For some time these lines were referred to by others as the " Halleyan 

 lines." Hansteen a century later introduced the term " isogonic lines," 

 which is now generally adopted. According to Hellmann, there is 

 reason for believing that some attempts had been made before those 

 of Halley to give on a globe or map a graphical representation of tlie 

 direction in which a compass needle points. It is conceded, however, 

 that Halley's was the first successful attempt ; his " variation chart " 

 was the first magnetic chart based on sufficient observational data to 

 give it immediately both practical and scientific value.- 



After the publication of his chart — the most important contribu- 

 tion to the observation material of terrestrial magnetism at the 

 time — Halley made no further attempt to establish a theory or to 

 improve on his early magnetic speculations. He appears finally to 

 have adopted the view so clearly formulated by Prof. Turner " — 



that the perception of the need for observations, the faith that something will 

 come of them, and the skill and energy to act on that faith — that these quali- 

 ties, all of which are possessed by any observer worthy the name, have at least 

 as much to do with the advance of science as the formulation of a theory, even 

 of a correct theory. 



1 Those interested in the history of the Halley charts may be referred to the various 

 articles by L. A. Bauer in Nature, May 23, 1895, p. 79, and in Terrestrial Magnetism, 

 January, 1896, and September, 1913 ; the last-named reference also contains a compilation 

 by J. P. Ault and W. P. Wallis of the magnetic results obtained on Halley's expedition. 



- Mountaine and Dodson, the authors of the second and revised edition (1744) of the 

 Halley Chart, and of the third (1756). published in connection with the latter a small 

 tract, "An account of the Methods used to describe Lines on Dr. Halley's Chart of the 

 terraqueous Globe, showing the variation of the magnetic needle about the year 1756 in 

 all the known seas. London, 1758, 4°." This tract was again published in 1784. 



^ Pres. Address, Sec. A, Brit. Assoc. Adv. Sci., 1911. 



