One of the nightmares of every government is the fear that its
securities will be counterfeited or tampered with. I have several times
mentioned precautions against such abuses in the shape of fine
engraving, watermarks, enameled paper, sensitive inks, etc. There are
numerous other devices which have been used with the same end in view.
The patterns here shown were printed on the backs of the stamps in blue
ink. The first is a band of interlaced lines, called a _burelage_. The
second is a sort of control number. The number differs for each stamp on
the sheet. The third resembles the lines in watered silk and is called
_moirée_. It covers the entire back of the sheet. Sometimes the stamps
are covered with a network which only becomes visible on the application
of certain chemicals. In this country the experiment has been tried of
breaking the fibre of the paper by pressing into the stamps a group of
tiny pyramids, called a grill. The idea was that the cancelling ink
would penetrate the broken paper and could not be removed.

We cannot finish our study of the material side of stamps without
reference to another feature, i.e., surcharges. Correctly speaking, a
surcharge is an added charge, but in philately the term is applied to a
variety of overprints, the majority of which indicate a reduction rather
than an increase in value. Years ago the word surcharge usually
suggested a makeshift, something of a temporary nature prepared to meet
an emergency and, therefore, interesting and likely to become valuable.
But our little weaknesses are now well understood by those who are
exploiting the commercial side of postage stamps and we have reason to
fear that many recent surcharges were made for revenue only and not from
any real necessity. The majority of surcharges are made to supply a
value which has been temporarily exhausted. For example, many of the
British Colonies obtained their supplies of stamps in London. It may