Sept. 12, 1878] 



NATURE 



527 



tubes of liquid having a maximum resistance of about 

 2, 4, 6, and 33 megohms respectively ; all but one were 

 furnished with adjustable wires by which their resistance 



could be diminished ; two are charged with equal parts of 

 water and glycerine, two with distilled water ; each has a 

 plug to throw the resistance out of circuit. 



Fig. 4. — M.crometer Discharger. 



These resistances gradually diminish by the absorption 

 of ammoniacal salts from the atmosphere, and this 

 necessitates occasionally the entire renewal of the fluid. 



Fig. 5. — Rotating Comir.u'^tor. 



As has been already stated, the paper deals principally 

 with the discharge in gases at atmospheric pressure. 

 Very elaborate series of measurements were made of the 



Fig. 6. — Table with Apparatus in situ. 



potentials (/>., differences of potential) requisite to produce 

 discharge at various distances between (i) plane surfaces, 



concentric cylinders, the diameter of the outer being con- 

 stantly 0-4895 inch, that of the inner being varied from 



(2) spherical surfaces of 3-inch radius of curvature, (3) I 0*4733 inch to 0-2865 i"ch, (4) a paraboloidal point and a 



