114 Rev. Mr Scoresby on the Uniform Permeability of 



The compass, in the next trial, was placed upon the library 

 chimney-piece, and the needle so far neutralized, that its vibra- 

 tions were reduced from 13 to 8 per minute. A pair of two 

 feet magnets were then taken to the farther extremity of a bed- 

 room on the same floor, separated from the compass by the 

 width of two rooms and a lobby, with two brick-walls, book- 

 case containing books, &c. ; and there, in a parallel position, 

 and about 10 inches asunder, presented to the compass. Their 

 action, though at the distance of 31 feet 8 inches, was quite evi- 

 dent and measurable. The amount of the influence of their 

 poles, in a mean of six sets of experiments, was 0'.23'^ *. 



Having at this stage of my experiments obtained a beautiful 

 pair of magnets (A), before referred to, from Sheffield, construct- 

 ed under the kind superintendence of Mr Abraham, I was en- 

 abled to accomplish every thing which my calculations had anti- 

 cipated. These magnets measure exactly 3 feet in lengtli, 2ith 

 inches in breadth, and |th of an inch in thickness. They are 

 made out of the best cast-steel, and tempered throughout, — the 

 ends, after the whole was hardened, having been reduced to a 

 gold colour, and the rest of the bars to a blue. The following 

 table exhibits their powers in combination, as they lie in their 

 case, 4 1 inches asunder, in that reduced state of magnetism pro- 

 duced by being repeatedly placed in unfavourable contact ; when 

 magnetised, however, to saturation, their action on the compass 

 is still more considerable. 



• In very delicate experiments, it is found to be advantageous to the ac- 

 tion of the compass gently to tap the glass with the point of the finger ; 

 without this precaution, the friction of the needle on its point may be pro- 

 ductive of considerable discrepancies. 



