Mechanical Philosophy, isS 



terning this mysterious kind of attraction has been 

 greatly augmented. The points in which it re- 

 sembles, and those in which it differs from electri- 

 city, have been more satisfactorily ascertained; 

 and a nearer approach made than formerly to a sys- 

 tematic arrangement of the magnetic laws. 



The unexpected and daring introduction of ma* 

 thematical principles and demonstration into the 

 dark regions of ekctrrcki^, by Mr. ^Epinus, was 

 mentioned, in a former page, as one of the signal 

 improvements of the last ceiitury. This ingenious 

 philosopher has done the same in magnetism, a^nd 

 with equal success.'^ And though this subjection 

 of the magnetic principles to the tnost precise and 

 definite of all species of investigation does not ap- 

 pear to have led, as yet, to any extraordinary dis- 

 coveries, or radical reforms ih theory; yet it has 

 been by no means without its use, and may con- 

 duct to invaluable acquisitions. 



The Mariner's Compass, within the period in 

 question, has been considerably improved. This 

 important instrument, after its invention in 1302^ 

 long remained in a rude and imperfect state. But 

 Dr. Knight's discovery of the mode of making ar- 

 tificial magnets, about the year 1744, together 

 with the results of some other experiments, en- 

 abled him to render the compass much more con- 

 venient and useful. To his improvements may be 

 added the further emendations of Mr. Smeaton^ 

 and Mr. M'Culloch, both of Great-Britain. 



The variation of the magnetic needle has been a 

 subject of much attention and of much ingenious 

 speculation, during the past century. The obser-* 

 vations made by Dr. Halley, and published in 

 1701, in the form of a variation chart, were of 



r See Tentamen Tieoria Magn. et Electr. Petrop. 1 759. See also thcf 

 Supplement to the Amtrltan Encydopadioi by Dos son, articles Electr ieitj 

 Jind Ma£/iftism, 



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