1(U 



THE STHUCTURE OF THE NUCI>EtrS. 



tiveness of Mascart's modification many times without falling below the require- 

 ments of a practical instrument. 



2. Original constants. — The method of work has been direct. I took the 

 well-known Elliott lecture form of quadiant electrometer and after determining the 

 original constants imi^oved on them successively. When the quadrants were 

 permanently charged with a small water battery of about 24 volts (retained 

 throughout), the results weie : temporary deflection per volt, 2.5 cm.; permanent 



Fig. I.— Electrometer Showing Capsule, Needle, and Quadrants in Place. Sectional Elevation. 

 Fjo. 2. — Cross Section of Capsule and Ionizer. 



deflection per volt, 1.7 cm.; scale distance, 440 cm.; period, 20 seconds; damping 

 ratio, 2/1. The low sensitiveness is due to the huge quadrants (12 cm. in diameter, 

 2.7 cm. high), and the small chaiging battery, the instrument being adapted to 

 an electrostatically highly charged needle. But as the case of the quadiants is 

 well-knowMi, and the whole improvement aimed at is confined to the needle, the 

 above term of comparison is adecpiate. 



The theory of the electrometer gives us approximately, d = a{V^ — \\) 

 ( J'j _ ( Fj, -f- Fj)/2), where 6 is the deflection, a a constant varying as the 

 effective circumferential breadth of the needle directly, and its distance from the 

 quadrants inversely. F,, V„, Fj are the potentials of the (piadrants and 

 the needle, respectively. If - F, = Fg, e = 2« F, Fg, where V^ is 1/2 the available 

 potential difference. For constant F,, this is the best adjustment of the water 



