658 Mr. O. U. Vonwiller on the Dielectric 
decreasing the amount of water in the vessel, and so 
varying the capacity. The depth was altered until the de- 
flexion obtained was about the same as that obtained with. 
the air-condenser when its capacity was such that the ar- 
rangement was in its most sensitive state. The water was 
then removed and ice-cold water poured into the vessel to 
the same level, and readings taken at frequent intervals as 
the temperature rose, the “temperature of the water being 
observed on two mercury thermometers, and the water being 
continually stirred. 
As the temperature rose the change of capacity was indi- 
cated by a change in deflexion. Between 0° and 15° there 
was on the whole a decided increase in deflexion, showing a 
decrease in capacity ; ; but in these earlier experiments, owing 
to irregularities in sparking 1t was impossible to say definitely 
whether the deflexion at 4° was higher or lower than that 
at O°, the variation in successive sparks being so great as to 
mask the change between these points. 
On several occasions there appeared to be an indication of 
a minimum deflexion in the neighbourhood of 4°; but on 
other trials, apparently equally reliable, this result was not. 
obtained. _ In any case the variation of capacity necessary to 
produce the apparent change would have been very small— 
much smaller than that obtained by Thwing, which would 
have produced an unmistakable change. 
Single sparks only were taken, the deflexions thus obtained 
being more regular on the whole than those in which a series 
of sparks were taken for each observation. 
In order to obviate this variation of deflexion due to the 
irregular sparking, another slider and detector were placed 
near the open end of the primary, and the deflexions pro- 
duced by this detector on a second magnetometer were 
observed. These deflexions should have been constant. With 
the secondary unchanged, when a series of readings were 
taken, although the deflexions produced by either detector 
varied considerably, the ratio of the two deflexions was found 
to vary to a much less extent. 
The following table shows a set of four readings of de- 
flexions of primary and secondary detectors, and the ratio of 
the two, no change being made during the four readings :— 





. | 
One On, 1000 6, /p. | 
| 315 28:7 911 
| 37-1 83-5 903 
| 34-4 31:8 924 
82°5 29°6 911 



