440 UR. C. T. R. WILSOX OX THE COXDEXSATIOX XUCLEI PRODLXED IX 
Discharge from a Pointed Platinum Wire in Aii\ Expansion made while the 
Discharge is taking place. 
Gauge reading (in 
raillims.) = /<. 
Result of 
expansion. 
Pointed M-ire positive. 
Pointed wire negative. 
141 
0 
0 
147 
0 
Fog 
1-5-5 
Fog 
Fog 
167 
Very dense fog 
Dense fog 
177 
Very dense fog 
Very dense fog 
The phenomena are simplest when, as in the observations given in the above table, 
the expansion is brought about while the discharge is taking place. No drops what¬ 
ever are seen, so long as the pressure fall is belovr a limit amounting to about 
15 centims., corresponding approximately to an exjiansion, T 2 /V 1 = 1‘25. The fogs, 
when the pointed wire was the negative terminal, were always obtained with a 
slightly lower expansion than was required when this was positive. With expansions 
only .slightly exceeding this limit the fogs obtained were very dense. The fogs have 
only a momentary existence, on account of the dust- or fog-removing property of the 
point discharge already referred to. This was especially the case when the point was 
positive. The fogs, during the few seconds or less for which they lasted, made 
manifest the violent eddying motion of the air which accompanies the discharge. 
It was found that, when the discharge was stopped before the expansion was made, 
the results were not so simple. These were reduced to some degree of regularity 
when the stopping of the discharge was brought about by suddenly connecting 
together by a wire the two terminals of the apparatus. For this purpose each was 
connected to one of two mercury cups made near together in a block of paraffin. A 
short wire was dropped into these cups while the discharge was taking place. This 
must very quickly have brought the pointed wire and the wet walls of the apparatus 
to the same potential. Any electrified particles produced by the discharge had, 
therefore, a greater chance of remaining in suspension on the air than would have 
been the case if the difierence of potential were allowed to exist for any considerable 
ti)ne after it ceased to be sufficient to produce a supply of the particles which act as 
carriers of the electricity. 
