40 
THE YOUNa SCIENTIST. 
the centre as at the outer edges, and it is 
in this that the operator's care and judg- 
ment are put to tlie highest test. Not 
only must the baclt be graded regularly 
from the centre to the edges, and liave its 
inner side as smooth and as perfectly fin- 
ished as the outside, but it must be also 
capable of producing a certain number 
of vibrations in a given time. 
In order that the operator may have a 
fixed scale to guide him in his work, let 
him take the length of the body of his in- 
strument, lay it out on a piece of wood, 
and divide it into 72 equal parts. This 
will form a very convenient scale of meas- 
urement. 
Let Jiiin then take his callipers, and ad- 
just them so that they will take in just 
two parts of the scale. Let him then 
work down the centre of the back until it 
is exactly two parts thick. He may then 
commence to thin the plate towards the 
outer edges until the edges show one part 
in such a manner as that the plate will 
grow gradually thinner from tlie centre to 
the outside, like a wedge. 
When this has been carefully done, he 
may test the i^late for sound. In order to 
discover the proper pitch of the back of a 
violin a considerable amount of experi- 
ment will be necessary on the part of the 
amateur. When the back of a violin has 
been properly w^orked out it should give, 
on percussion, the note Do of 512 single 
vibrations in a second. It requires a good 
ear to perceive this, for the reason that a 
sound emitted by a piece of wood is not so 
clear or so well defined as that given out 
by a musical instrument. The best way 
to arrive at a good result is to procure a 
sliding pite'/i-pipe and set it at Do 512 vi- 
brations, or C on the G string of a good 
violin properly tuned. Let the amateur 
then understand that there are three no- 
dal lines ill the back of the violin (or lines 
of no vibration). One of these lines runs 
down the centre of the back, and the two 
others cross this centre line at right 
angles, one through the middle of the 
larger end, and the other through the 
middle of the smaller end (when I say the 
middle I mean about the middle). Let 
the amateur take hold of the back where 
two of these nodal lines intersect with his 
forefinger and thumb, and strike the plate 
with his knuckle or with a piece of wood, 
and he will find that it will emit a very 
well defined sound, which he will find, on 
blowing into his pitch-pipe, to be sharper 
or flatter than the note given by the pitch- 
pipe. If the note emitted by his newly- 
made back be flatter than 512 vibrations 
in a second, he may throw the back away 
as worthless — the wood is of bad quality, 
audit will never make a good violin. If, 
on the contrary, the back gives a sharper 
note than his pitch-pipe, he is all right. 
All he has to do in that case is to care- 
fully thin the back with fine sand-paper 
until it gives the required note. When 
all this has Ijeen carefully done, he may 
attach the back to the ribs. In doing 
tills let him take thin hot glue, and with 
a brush run it around the edge of the 
plate and also around the ribs where they 
are to be joined to the plate— this must be 
done quickly, that the glue may not have 
j time to set. He then lays the ribs which 
are still attacliedto the mold on the back, 
land, with small clamps, brings them 
i tightly together. The clamps should not 
I be removed before eight or ten hours, 
j The next operation is the finishing of 
jthe belly or upper plate of the violin. 
This will be found much more pleasant 
than the working of the back — first, be- 
cause the wood is softer, and secondly, 
because it may be made of equal thick- 
ness throughout. Indeed, the bellies of 
the best violins are of this style— equal 
thickness throughout. But it must be 
borne in mind that the belly must be 
thinner than the thickest part of the back. 
The timber of the belly is more resonant 
than that of the back, and, for the same 
dimensions, gives a sharper tone. Con- 
sequently, if the both tables were of the 
same degree of thickness, the tone of the 
belly would be altogether too high for 
