PRESIDENTS ADDRESS—SECTION A. 49 
that has been rubbed be brought into this curious polarised state? 
Ought we to imagine that gravity is caused by ether stresses ? 
The answer to this last question was given long ago, and is to 
the effect that of course we can represent the actual state of 
gravitation on the earth’s surface by a distribution of stresses, 
but they would require to be very great, no less than a pressure 
of 37,000 tons weight per square inch in a vertical direction, 
combined with an equal tension in all horizontal directions—this 
is about 3,000 times the breaking strength of steel. (Tait’s 
“ Properties of Matter.”) 
Before we push our enquiry as to the mechanism of electriti- 
cation any further, it is necessary for us to glance rapidly at the 
more prominent features of the relations generally summed up 
under the title of electro-chemistry. Modern researches have 
only served to strengthen Faraday’s position, that when a current 
passes through an electrolyte the amount of decomposition 
brought about is strictly and exactly proportional to the time 
integral of the current. This quantity will for the future be 
referred to as a “quantity of electricity,” and must not be 
imagined in any way to connote that electricity is a substance— 
or even that it is a state of motion of ether—though much might 
be said for both of these views. If we extend the definition so 
as to discriminate between those substances, which, under certain 
circumstances, travel in the nominal direction of the current, and 
those which travel in the reverse direction, we may say that 
during electrolysis one ion carries a certain positive quantity of 
electricity, while the other carries an equal negative quantity. 
Adopting the ordinary atomic theory of chemistry, the results of 
experiment may be summed up in the statement that all mono- 
valent atoms require the same quantity of electricity to free 
them on the electrodes, and the quantity of electricity required 
to pass a divalent atom is twice the quantity required for a 
monovalent atom ; for a trivalent atom, three times, and so on. 
Further, I think it may be considered as established that the 
apparent decomposition of an electrolyte into its ions by a current 
is really merely a process of direction, and is not a real process 
of decomposition. Taking the case of a solution of copper- 
sulphate, for instance, it is probably not true to say that the ions 
are forced apart by the current, or rather by the electric force, 
but that continuous dissociation is a normal state of such a 
solution, and that all the electric force does is to cause a con- 
gregation of ions at the two electrodes. This conclusion is 
deduced from the fact that electrolytes appear to obey Ohms’ 
law very exactly, which would be a very unlikely or even impos- 
sible thing to happen if work were required to produce dissocia- 
tion as well as to make the ions give up their charges. Some 
philosophers have regarded the facts of electrolysis as showing 
that there must be a real difference between a positive quantity 
D 
