Intelligence and Miscellaneous Articles. 155 



formula gave 



w 



ith 



^ 4mm' 



p 



0= / s> 2 



si 



c 



Iii my experiments = 437% and 2^>r 2 =32171 % 6 centimetre- 

 grammes, the lever having been made of a geometrical form. 



The following numbers represent the potential of an element 

 of the pile — that is to say, the quantity of electricity which would 

 be shed by the pole of that pile upon a sphere of 1 centim. radius ; 

 they are expressed in electric units, the unit being the quantity of 

 electricity which, acting upon itself at 1 centim. distance, produces 

 a repulsion equal to 1 gramme. 



Voltaic pile 0-03415, circuit open. 



Pile (zinc, sulphate of copper, copper) 0-02997, ,, 

 „ (zinc, acidulated water, copper, ) a-ao^-ao 



sulphate of copper) J ' 



„ (zinc, salt water, carbon, per- 1 a;a~oqo 



oxide of manganese) J ' 



„ (zinc, salt water, platinum, chlo- 1 A .(\'oo^ 



ride of platinum) J ' 



„ (zinc, acidulated water, carbon, 1 A.Agoo- 

 nitric acid) J ' 



These numbers are maxima values, obtained at the moment when 

 the pile had just been charged ; but these potentials rapidly grow 

 less as the pile gets older. The sulphate-of-copper pile alone re- 

 mains for a pretty long time near the given number ; but it under- 

 goes variations which may reach one twelfth of its value, more or 

 less. — Comptes Rendus de VAcad. des Sciences, Jan. 3, 1881, t. xcii. 

 pp. 32-34. 



A STUDY ON SPECTROPHOTOMETERS. BY M. A. CROVA. 



The comparison of two spectra proceeding from two different 

 sources of light is easily obtained by covering half the slit of a 

 photometric spectroscope with a small rectangular prism, of which 

 the edge cuts the slit normally into two parts. One half receives 

 one of the lights directly, the other by total reflection the other 

 light placed laterally. In this case the slit must be horizontal ; 

 and if the prism is well cut and free from aberration, the clean 

 image of the spectral lines and that of the edge of the prism are 

 obtained simultaneously — the latter appearing as a very fine line 

 separating the two spectra to be compared from one another. 



