1G0 



Intelligence and Miscellaneous Articles. 



X 



ment was employed. The adjoin- 

 ing figure represents a plate of 

 copper pyrites 40 millims. broad, 

 70 long, and 7 thick; into it are 

 inserted, at a distance of 35 mil- ^ 

 lims. from each other, two copper r— 

 pins of somewhat conical form, 

 and having a mean diameter of 9 

 millims. Both pins are very care- 

 fully cut and platinum-plated, and 

 the upper one has a copper projec- 

 tion b. This projection being 

 heated by a non-luminous lamp- 

 flame, whilst the lower part of 

 the plate of pyrites, together with - 

 the copper pin fixed therein, is 

 cooled in water, a current is 

 obtained in the closed circuit 

 formed by the copper wires c c, 

 whose intensity after some time becomes constant — care being taken 

 to protect from fluctuations the flame applied to the projection. The 

 constants of this small pile were compared with those of a Daniell's 

 element, arranged in the customary way. The copper surface which, 

 in this element, was immersed in the liquid opposite to the cylinder 

 of amalgamated zinc had an area of one square decimetre ; the 

 liquids consisted of a completely saturated solution of sulphate of 

 copper, and of a mixture of six parts (by weight) of water and one of 

 sulphuric acid. 



If L denote the effective resistance of a pile, E its electromotive 

 force, a; the resistance in the closed circuit, and I the intensity of 

 the current, we have, as is well known, the relation 



L + o> 

 The resistance being increased by r, the diminished intensity of 

 the current will be expressed by 



E 

 L -f- w + r 

 To determine E and L, the current was passed through a coil of 

 wire placed, in the requisite manner, at the distance dfrom a mag- 

 netometer, and the deflections I and i were measured which corre- 

 sponded to the resistances (L + w) and (L-fw + r). In all experi- 

 ments eu and r had the values 4*46 and 16*00, respectively. The 

 distance d of the coil of wire from the magnetometer was 1 metre 

 with the Daniell's element, 0*5 of a metre with the pile of copper 

 pyrites, and 0*25 of a metre with the pile of pyrolusite. Accordingly, 

 when comparing the piles, we shall have to employ the formulae 



L= 1^.-4-46, 



I — I 



E=/^ + 16W 



