y than not to make matters worse,
as it should always be borne in mind that glued surfaces always require
pressing together, however well they may fit. Glue contracts as it
dries, and in the process apparently disperses and clings to any other
bodies rather than to itself. To put this in another way, if air is
allowed to insinuate itself between the two surfaces which it is
desirable to bring into closest conjunction, the contraction,
particularly if good, while in progress, will cause a separation in
the central mass of the glue, while the two surfaces will be left as
before, independent of each other, but more clogged. Pressure must
therefore be invariably brought to bear behind the opposing parts, so
as to drive out the air from between and prevent its re-admission--the
necessity of an exact correspondence of the parts will be obvious--at
the same time the glue is to some degree forced into the pores of the
surfaces, and when the moisture has dispersed among the myriads of
cells composing the structural growth of the wood and finally
evaporates from the external ones, the glue, having hardened, will hold
the parts together with a tenacity that can only be overcome by
prolonged application of moisture or actual destruction of the parts.

There is one very important consideration in connexion with glueing
operations that must not at any time be lost sight of--that of
atmospheric temperature. Much trouble may be brought about by
inattention to this help or obstruction, for it will act both ways
according to circumstances. In the glueing of important parts in the
construction of pianofortes, the operators are careful to have the
temperature of the surrounding atmosphere sufficiently elevated, as
well as heating those portions of the structure which are to be
accurately and lastingly joined, and particularly where hard woods and
smooth surfaces are brought together. The violin repairer must
strictly follow the same rule. The degree Fahrenheit at which glueing
operations are best conducted may be roughly estimated as nearly
seventy. The reason for this is that the nature of good glue is to
coagulate or "set" rapidly in a cool atmosphere and in this state--not
perceptible at once to the eye--it will resist a considerable amount
of pressure, the surfaces that should exactly cohere, slipping aside
and the whole work having to be done over again, perhaps with fresh
damage.

To return now to our loose fingerboard, an old fash