KENT AND TAYLOR. 



aperture; each echelon bed rotates on an axis at its center; the Hilger 

 micrometer is fitted with one fixed and two movable cross-hairs as 

 shown in Figure 2. 



^J7> 



Fig. lb. 



Figures la and lb. S, slit; L, L, lenses; E, echelon; P, prism; 

 O, ocular. 



Figure 2. SS', fixed crosshair; MM', MM' movable system; 

 LL', spectrum line. 



A Littrow mount spectroscope consisting of a Petitdidier 

 achromat — focal length 30 feet, aperture 6"; and an An- 

 derson grating — aperture 3f " vertical by 5" horizontal, 

 15,000 lines per inch, used in the third order. 



A 5 K. W. transformer, 1 10 to 30,000 volts ratio of trans- 

 formation, fed by a 60 cycle Holtzer-Cabot 4.5 K. W. gen- 

 erator. Various large induction coils capable of giving 6" 

 sparks and operated by a rotary mercury break and an 

 electrolytic interrupter, had proven insufficient. 



A vacuum arc of construction as indicated in Figure 3. 



