1815.] Experiments on pure Nickel. 61 



circumference into 17 parts. Tlie arc 1 1 1 is one of these parts : 



17 17 17 



the continued line 1 1 1 is equal to the central diameter 1 O 1. 



17 16 17 O 



Now this central diameter is a unit ; for the central circle and its 

 diameter are respectively units, which are heterogeneous with each 

 other. All the parallel lines, 111,111, &c. are equal to this 



10 1 S 1 2 



last unit. These lines are the greatest which can be drawn between 

 the two extreme circumferences of each ring, and they may be 

 considered as the diagonals of those rings, in the same manner as 



o 



the diameter 1 O 1 can be considered as the diagonal of the central 







circle. We have, then, between the diagonal of the central circle 

 and the diagonal of the rings, the same analogy as between the 

 central circle itself and these rirjgs ; the central circle and the rings 

 are both superficial units, and maxima ; the diagonals of the central 

 circle and of the rings are both linear units, and also niaximai This 

 geometrical construction of the problem, as presented by fig. l, is the 

 only one which can be right ; because all the straight lines of this 

 figure are either maxima oy minima, in such a manner that if they be 

 maxima as lines, they are minima as being opposite to an angle or 

 an arch which is a minimum-, and if tiiey be minima as lines, they 

 sire maxima, as being opposite to an angle or an arch which is a 

 maximjon, as I shall demonstrate at length in anotlier paper. These 

 lines, then, cannot be greater or less than tliey arc. M. le Gendre, 

 at the end of his Geometry, has given an algebraical solution of 

 this problem, but he has not given the geometrical construction of 

 his formuhe : that construction was in fact impossible, without de- 

 stroying the law of continuity. 



Article III. 



Some Experimetils on pure Nickel, its Magnetic Quality, and its 

 Depwimmt when united to other Bodies.* By \\. A. La'n)padlu>. 



J. ArncR having in 179« discovered a method of obtaining pure 

 mallfalilt- nickel by means of an oxygen gas fire, eitiicr from Frei- 

 berg Blcispeise, or from the common rcgulus of nickel obtained 

 from cop|)er nicktl by the usual process, I occasionally made a 

 number of accurate oxj)criinents on many of the properties of this 

 metal, which luid been hitherto examined only in a cursory manner. 

 121 grains of .^/me gave mc 4S grains of nickel, and 123 grains of 

 copper nickel ore gave me 63 grains of the pure metal. 



2. Magnetic Power of Nickel. 

 The magnetometer described iii the preceding paper gave the 



• TroDilatcd fram Schwci^j^cr'i* J.iurnril fiir t'hpinic iiiiJ Plivsik, x. IT-I. ISK 



