565 
of Edinburgh , Session 1877-78. 
This result, in my opinion, establishes the truth of Clark-Maxwell’s 
hypothesis, that the greater electromotive force required at the 
smaller distances is due to the existence of condensed gas on the 
surface of the discs. Precisely similar results were obtained when 
hydrogen was substituted for air. 
The method, when applied to measure the difference of potential 
required to produce a *5 centimetre spark at different pressures of 
the air, shows that for the range between the atmospheric pressure 
and twenty mm., 
V = ’0458 + 203 p) 
where p denotes the pressure in millimetres of mercury. 
The electric strengths of several gases were determined by com- 
paring the differences of potential required to pass a *5 centimetre 
spark through the gas at 746 mm. pressure. 
Dielectric. 
Electric Strength. 
Air, 
. 1 
Carbonic acid, . 
. *95 
Oxygen, 
. *93 
Hydrogen, 
. *63 
Coal gas, 
. *93 
Several series of observations of the difference of potential re- 
quired to produce a spark between spherical surfaces for distances up 
to 15 centimetres confirm the result published in the paper already 
referred to, that the difference of potential is proportional to the 
square root of the length of the spark. 
3. On the Compressibility of Water, Sea- Water, a four per- 
cent. Chloride of Sodium Solution, Mercury, and Glass. 
By J. Y. Buchanan, M.A., F.B.S.E. 
4. On the Action of Heat on some Salts of Trimethyl-Sulphine. 
By Professor Crum Brown and J. Adrian Blaikie, Esq. 
(Abstract.) 
The authors describe the preparation, properties, and action of 
heat upon the following compounds of trimethyl-sulphine : — 
VOL. ix. 4 F 
