Halley's earliest equal variation chart

Abstract

In Nature, of May 23, 1895, the writer made known the finding of a Halley isogonic chart in the British Museum which had apparently escaped the attention of modern magneticians and bibliographers and to which Halley himself, as far as has been ascertained, made no reference. Upon seeing the notice, Mr. Thos. Ward of Northwich, England, made known in the following number of the same periodical the fact that he likewise possessed a copy, bound up with other charts of the 17th and 18th centuries. Through his courtesy and kindness the JOURNAL is enabled to present the first facsimile reproduction, as far as known.