442 ME. C. T. E. WILSON ON THE CONDENSATION NUCLEI PEODUCED IN 
Hydrogen. 
The results oljtaiiied with hydrogen Vvdien the expansion was made while the 
discharge was taking place are given in the table which follows :— 
i 
; Gauge reatUng (in 
1 millims.) = p. 
Eesult of 
expansion. 
Pointed wire positive. 
Pointed vore negative. 
I 14-4 
0 
0 
1 1.50 
0 
Shower 
i 15G 
0 
Fog 
1 157 
Slight fog 
Fog 
158 
Slight fog 
Dense fog 
The expansion retpiired is, it will be seen, practically the same as in air. The fogs 
were again observed with slightly less expansion v/hen the wire was negative than 
when it v/as positive. 
The results of a second series of exjjeriments made some weeks later are contained 
in the next table. 
Gauge reading (in 
millims.) = p. 
Eesult of exjjansion. 
Pointed wire positive. Pointed wire negative. 
145 
0 0 
15o 
Slight shower Fog 
150 
Fog Fog 
In a third independent series oljtained some months later, the following numbers 
were obtained :— 
Gauge reading (in 
millims.) = p. 
Eesult of 
expansion. 
Pointed wire positive. 
I’ointed wire negative. 
1.32 
0 
0 ; 
146 
0 
Few drops ' 
157 
Dense fog 
Dense fog 
The positive fogs thus obtained are much more evanescent than the negative, 
appearing generally as a momentary Hash of brightness in the appai'atus, while the 
