3$ Mechanical Philosophy. [Chap. I. 



vations made by Dr. Halley, and published in 

 1701, ill the form of a variation char^t, were of 

 great use to navigators, and contributed not a lit- 

 tle toward reducing the principles of this variation 

 to something like an intelligible form. The next 

 attempt of the same kind, worthy of notice, was 

 tliat of Euler. This philosopher, equally remark- 

 able for the extent of his learning, and the vigour 

 and comprehensiveness of his mind, undertook, 

 about the middle of the century, to account for the 

 magnetic irregularities, and to ascertain the posi- 

 tion of the needle in every part of the earth. He 

 executed his task with singular ingenuity and per- 

 severance, and with a plausible appearance of 

 success. But his theory, and the whole structure 

 founded upon it, were soon found liable to such 

 objections, that they were considered of little value, 

 excepting so far as they might furnish a guide in 

 the further prosecution of the inquiry. Since the 

 time of Euler, many others have exerted their ge- 

 nius in the same investigation; but without pro- 

 ducing more certainty or satisfaction. Among tlie 

 Jatest explorers of this dark but important sub- 

 ject, Mr. Churchman, a respectable citizen of 

 America, deserves to be honourably mentioned. 

 He has, in his own opinion, made valuable im- 

 pro\ ements on the theories of Halley and of Eider ; 

 corrected various errors into which those great 

 philosophers fell ; and given an hypothesis which 

 bids fair to be of more practical utility than theirs 

 to the nautical adventurer. How soon this hypo- 

 thesis may be brought to the test of a complete 

 course of experiments, or how it may bear this 

 test, when subjected to it, are questions yet to be 



