and falling tides may be utilized for
driving dynamo machines, by which electricity may be generated for
lighting the coast cities, and it is not unreasonable to expect that
such an apparatus will soon be provided; and in such an event gas
companies would suffer.

It is a well known fact among electricians that the volume and tension
of electricity vary both in the earth and in the atmosphere at
different sections of the earth's surface, and I conceive that we may
yet find means of utilizing this differential tension of electricity;
indeed, it is reported that during a recent storm the wires of an
ocean cable were grounded at both ends and a sufficient current for
all practical purpose flowed from the European to the American
continent, with all batteries removed, showing that the tension was so
much greater in Europe as to cause the electricity to flow through the
copper cable to this side in preference to passing through the earth
or the sea. It is also said that during an east-going storm it was
found impossible to work the telegraph lines between New York and
Buffalo, but on taking off the batteries at both ends and looping the
ends of the wire in the air, that a constant current of electricity
passed from Buffalo to New York, and the line was kept in constant use
in that direction without any battery connection until the storm
abated. Now, how far or to what advantage we may be able to utilize
this differential tension of electricity in the earth and the air, we
cannot now say; but I think that we may justly look for valuable
developments in this direction.

If, as I verily believe, a process will soon be discovered by which
dynamic caloric can be produced by the oxidation of petroleum with
non-luminous combustion in an insulated chamber, as we now oxidize
zinc, electricity will then be obtained from so small a weight, and at
such a low cost, as to insure aerial navigation beyond a doubt. Not
with balloons and their cumbrous inflations, but with machines capable
of carrying the load, and traveling by displacement of the air at high
velocities. Therefore we may expect that aerial navigation will be
developed in the near future to be one of the greatest enterprises of
the world.

And lastly, will it pay to use luminous combustion as a first power
for generating dynamic caloric for use as a second power, as is now
practiced?

At the University of Pennsylvania, in Philadelphia, gas is consumed in
an Otto gas engi