avoided the use of mathematical language. Algebra is an admirable
tongue, but there are many occasions where it can only be used
with much discretion.

Nothing would be easier than to point out many great omissions
from this little volume; but some, at all events, are not
involuntary.

Certain questions which are still too confused have been put on
one side, as have a few others which form an important collection
for a special study to be possibly made later. Thus, as regards
electrical phenomena, the relations between electricity and
optics, as also the theories of ionization, the electronic
hypothesis, etc., have been treated at some length; but it has
not been thought necessary to dilate upon the modes of production
and utilization of the current, upon the phenomena of magnetism,
or upon all the applications which belong to the domain of
Electrotechnics.

L. POINCARÉ.





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EDITOR'S PREFATORY NOTE