STANDARDIZATION AND EFFICIENCY OF THE FOG CHAMBER. 



33 



approximation to the true value. A comparison of n and n n r would in 

 such a case show the percentage of nuclei of irregular size which have 

 failed of capture, the number being n n'. 



At the same time it must always be recalled that no adequate theory 

 of coronas exists and that therefore the meaning of n' is obscure. We 

 must in any case place a part, if not all, the discrepancy between n and 

 n' within the province of such a theory. The need of it is particularly 

 manifest for the large coronas, in which there is accentuated superposition 

 of interference and diffraction. Small coronas may be tested by coinci- 

 dent results obtained from subsidence, and the agreement is then well 

 within the errors of observation. 



TABLE 1 2. Comparison of nucleations. 



EFFICIENCY OF LARGE AND SMALL FOG CHAMBERS, ATTACHED TO 



THE SAME VACUUM CHAMBER. 



27. Fog chambers. The large apparatus used in the experiments* 

 for the displacements of ions showed relatively low degree of conden- 

 sational efficiency. It was therefore thought worth while to compare 

 fog chambers both larger and smaller than the normal size (Xo. i) with 

 regard to their powers in catching nuclei. In addition to the large re- 

 ceiver (Xo. 2) specified, an exceptionally small fog chamber (Xo. 3^ 

 was specially constructed. Experiments were made with each in turn, 

 both for the case of the vapor nuclei of dust-free air and of ions. 



*See chapter III, fig. 12. 



