80 Intelligence and Miscellaneous Articles. 



In a second copy of the same instrument, which I have the 

 honour to place before the Academy, the system of two hemispheres 

 is contained within a concentric spherical envelope, which is 

 connected with the earth. This arrangement increases the 

 sensitiveness of the instrument, and protects it from air-currents 

 as well as from extraneous electrical influences. 



If a and b are the radii of the two concentric spheres, we have 

 the formula 



In this case we have a=3*9 centims., 6=4*92, p = 3*322 grams. 

 Hence if we place a millimetre scale at 1 metre from the rule, 

 we have for the value of the deflection, 

 d=0*00373V 2 . 



If Y is expressed in volts, we have 



fcO*0000140V 3 . 



It is desirable to multiply optically the sensitiveness of the 

 instrument by reading the deflections with an ocular which 

 magnifies 15 to 50 times. This also diminishes in the same 

 ratio the small deformation which the system of the spheres 

 undergoes owing to the deflection. — Comptes Eendus, March 22, 

 1886. 



SIMPLE DEMONSTRATION OF THE ELECTRICAL RESIDUE. 

 BY FR. STENGER. 



If two strips of tinfoil are fastened at a suitable distance on a 

 glass tube which has been evacuated as completely as possible, and 

 are connected with the electrodes of an induction-coil, continuous 

 electrical currents are formed in the interior, and the gas becomes 

 intensely luminous. If, then, the two tinfoil rings are insulated, 

 the tube becomes luminous at frequent intervals, and frequently 

 for several minutes together. This doubtless arises from the for- 

 mation of a residue on the sides of the glass. The experiment was 

 made in a far more striking manner as follows : — In a glass tube, 

 about 2 centim. in the clear, closed at one end, a thin metal foil 

 was introduced so that it covered about half the inner side. A 

 wire soldered to this plate was hermetically sealed in the tube, and 

 was provided on the outside with a small knob. Opposite the 

 metal cylinder a strip of tinfoil was fastened. This small Leyden 

 jar was then rarefied as completely as possible, and hermetically 

 sealed. If this was charged from a small electrical machine for 

 ten or fifteen minutes the residual electricities could be discharged, 

 producing a bright illumination in the tube. This method of ren- 

 dering visible very small quantities of electricity might possibly be 

 used in repeating in another form the experiments of Rowland and 

 Nichols*, on the formation of the residue in quartz and calc-spar, 

 which are of theoretical interest. — Wiedemann's Annalen, No. 6, 

 1886. 



* Rowland and Nichols, Phil. Mag. [5] xi. p. 414 (1881). 



