VOL. LXVl.] PHILOSOPHICAL TUANSACTTONS. IIQ 



repeat the same process, that the present machine would acquire a degree of 

 force superior to what the original ever possessed ; for much depends on time and 

 a due position. If to these was added a fresh impregnation of each single bar, 

 by the means hitherto made use of, we would probably possess a larger fund of 

 magnetic power, than exists in any artificial magnet now in being. But if this 

 cannot be obtained, if an able person cannot be prevailed on to renew its vigour 

 in this manner, it might possibly afford the curious some satisfaction, to know 

 whether, in its present state, it loses any force, or acquires fresh virtue; to know, 

 with some degree of precision, how much weight it will now suspend; and to 

 observe annually its variation. A trial of this nature demands no small atten- 

 tion. Even the motion of a carriage in the street, though at such a distance as 

 the society's apartments, will make a considerable variation. 



It is not known, that the Doctor left behind him any description of a com- 

 position he had matle to form artificial load-stones. Many of his friends have 

 seen such a composition; which retained the magnetic virtue in a manner much 

 more fixed, than either any real load-stone or any magnetic bar, however well 

 tempered. In the natural ones he could change the poles in an instant, so like- 

 wise in the hardest bars; but in the composition the poles were immoveable. He 

 had several small pieces of this composition, which had strong magnetic powers. 

 The largest was about half an inch in breadth, very little longer than broad, and 

 near a quarter of an inch thick. It was not armed, but the ends were power- 

 fully magnetic ; nor could the poles be altered, though it was placed between two 

 of his largest bars, and they were very strongly impregnated. The mass was 

 not very heavy, and had much the appearance of a piece of black lead, though 

 not quite so shining. It is believed he never divulged the composition; but Dr. F. 

 thinks he once told him, the basis of it was filings of iron, reduced by long-con- 

 tinued attrition with water to a perfectly impalpable state, and then incorporated 

 with some pliant matter, to give it due consistence. Perhaps some of his ac- 

 quaintance may have been more fully informed of this circumstance; and it may 

 be rendering great aid to future inquirers, to know every thing that can be col- 

 lected relative to so curious a subject. 



Each magazine, in the two parts of this machine, consists of 240 bars, dis- 

 posed in 4 lengths ; every length containing 6o bars, placed in 6 courses or layers, 

 in contact with one on another; and 10 in each course, placed side by side, in 

 contact also. The bars being very nearly of a size, the ends of those in one 

 length are in contact with the corresponding ends of those in the adjacent 

 lengths. The magnetical north ends of these bars, in each magazine, are all 

 directed one way towards n; and the south ends the contrary way towards s; 

 thick plates of iron cover these ends n and s; the junction of the ends of the 

 bars fall under brass braces. 



