396 Additional Notes. 



4. The magnetic fluid moves, without any considerable ob- 

 struction, through the pores of iron and soft steel : but it is more 

 and more obstructed in its motion as the steel is* tempered harder j 

 and in hard tempered steel, and in the ores of iron, it is moved 

 with tJie greatest difficulty. 



. 5. When tlie quantity of tlfis fluid contained in iron is such 

 that the accumulated attraction of a particle for all the iron ba- 

 Iriuces, or is equal to, the repulsion of all the fluid which the iron 

 contains, the quantity may be said to be the natural quantity of the 

 iron, which may then be said to be in its natural state. 



6. The magnetic fluid may be abstracted from one end of a 

 magnetic bar, and constipated in the other, and on this depends 

 the exertion of its force. In other words, the condensation and 

 motion of the magnetic fluid are subject to the same laws (mu- 

 tatis piutandis), in the opinion of this philosopher, as the electric 

 fluid on the Franklinian theory, the motion and sensible signs of 

 which depend on thep/'j/s and minus states, or the deficiency cUid 

 redundancy of the same fluid in different bodies. 



J^ote (K), p. 37- — '' As every piece of iron which was made 

 magnetical by the touch of a magnet became itself a magnet, many 

 attempts \\-ere made to improve these artificial magnets, but with- 

 out much success, till Servdngdon Savary, esq. made thenioi hardened 

 steel bars, which were so powerful, tlrat one of. them, weighing 

 three pounds avoirdupois, would lift another of the same weight. 



" After this Dr. Gowin Knight made very successful experi- 

 ments on this subject, which, though he kept his method secret, 

 seems to have excited others to turn their attention to magnetism. 

 About this time the rev. Mr. Michel invented an equally efficaci- 

 ous and more expeditious way of making strong artificial magnets, 

 which he published in the end of the year 17^0, in which he ex- 

 ])lained his method of what he called the Double Touch, and 

 whicli, since Dr. Knight's metliod has been known, appears to be 

 somewhat different from it. 



" This method of rendering bars of hardened steel magnetical 

 consists in holding vertically two or more magnetic bars nearly 

 parallel to each other, with their opposite poles very near each 

 other (but, ne^•ertheless, separated to a small distance) : these are 

 to be slided over a line of bars, laid horizontally, a few times back-i 

 ward and forward. 



'• \\hat Mr. Michel proposed by this method was, to include a 



