52 



VAPOR NUCLEI AND IONS. 



pound (iron stopcock) and the inflow of the external air absolutely 

 avoided. The cock, moreover, is in this way virtually floated in oil; 

 though no such provision is possible to avoid leakage from F to V 

 tli rough C as already stated. 



The goniometer for the measurement of the angular diameter of the 

 coronas is shown somewhat indistinctly at D. The small vertical plate 

 which serves as the eye rest is 40 cm. from the axis of the fog chamber, 

 to which it is rigidly attached, but with freedom of rotation about a 

 vertical and horizontal axis and translation along the latter. The arms 

 are 30 cm. long, opened and closed by a tangent screw. The point 

 source of light (not shown, part of a Welsbach mantle) lies 250 cm. 

 behind the fog chamber, in the same horizontal plane. 



Fig. 26. Disposition of apparatus in case of fog chamber (F) and vacuum chamber 

 (V) connected by a 4-inch exhaustion pipe, etc. 



The X-ray bulb, adjustably placed with the induction coil and inter- 

 rupter on a table provided with wheels, could be moved as near to the 

 fog chamber, or remote from it, as desirable, with facility. 



The fog chamber itself was a cylindrical jar of glass, provided with a 

 metallic face held in place by bolts and tightened by a rubber gasket. 

 Wax-resin cement was used in liberal quantity everywhere, and internal 

 metallic parts were so far as possible covered with a coat of it. In later 

 experiments a cylinder of wet cloth was placed in the tube between C 

 and F, to saturate air, in addition to the rectangular framework within 

 the fog chamber. 



